class Hash - Documentation for Ruby 4.0
Description: class Hash: A \Hash object maps each of its unique keys to a specific value. An array index is always an integer.
Keywords: ruby,class,Hash

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# class Hash

A Hash object maps each of its unique keys to a specific value.

A hash has certain similarities to an `Array`, but:

- An array index is always an integer.

- A hash key can be (almost) any object.

### Hash Data Syntax

The original syntax for a hash entry uses the “hash rocket,” `=>`:

    h = {:foo => 0, :bar => 1, :baz => 2}
    h # => {foo: 0, bar: 1, baz: 2}

Alternatively, but only for a key that’s a symbol, you can use a newer JSON-style syntax, where each bareword becomes a symbol:

    h = {foo: 0, bar: 1, baz: 2}
    h # => {foo: 0, bar: 1, baz: 2}

You can also use a string in place of a bareword:

    h = {'foo': 0, 'bar': 1, 'baz': 2}
    h # => {foo: 0, bar: 1, baz: 2}

And you can mix the styles:

    h = {foo: 0, :bar => 1, 'baz': 2}
    h # => {foo: 0, bar: 1, baz: 2}

But it’s an error to try the JSON-style syntax for a key that’s not a bareword or a string:

    # Raises SyntaxError (syntax error, unexpected ':', expecting =>):
    h = {0: 'zero'}

The value can be omitted, meaning that value will be fetched from the context by the name of the key:

    x = 0
    y = 100
    h = {x:, y:}
    h # => {x: 0, y: 100}

### Common Uses

You can use a hash to give names to objects:

    person = {name: 'Matz', language: 'Ruby'}
    person # => {name: "Matz", language: "Ruby"}

You can use a hash to give names to method arguments:

    def some_method(hash)
      p hash
    end
    some_method({foo: 0, bar: 1, baz: 2}) # => {foo: 0, bar: 1, baz: 2}

Note: when the last argument in a method call is a hash, the curly braces may be omitted:

    some_method(foo: 0, bar: 1, baz: 2) # => {foo: 0, bar: 1, baz: 2}

You can use a hash to initialize an object:

    class Dev
      attr_accessor :name, :language
      def initialize(hash)
        self.name = hash[:name]
        self.language = hash[:language]
      end
    end
    matz = Dev.new(name: 'Matz', language: 'Ruby')
    matz # => #<Dev: @name="Matz", @language="Ruby">

### Creating a Hash

You can create a Hash object explicitly with:

- A hash literal.

You can convert certain objects to hashes with:

- Method `Kernel#Hash`.

You can create a hash by calling method `Hash.new`:

    # Create an empty hash.
    h = Hash.new
    h # => {}
    h.class # => Hash

You can create a hash by calling method `Hash.[]`:

    # Create an empty hash.
    h = Hash[]
    h # => {}
    # Create a hash with initial entries.
    h = Hash[foo: 0, bar: 1, baz: 2]
    h # => {foo: 0, bar: 1, baz: 2}

You can create a hash by using its literal form (curly braces):

    # Create an empty hash.
    h = {}
    h # => {}
    # Create a +Hash+ with initial entries.
    h = {foo: 0, bar: 1, baz: 2}
    h # => {foo: 0, bar: 1, baz: 2}

### Hash Value Basics

The simplest way to retrieve a hash value (instance method `[]`):

    h = {foo: 0, bar: 1, baz: 2}
    h[:foo] # => 0

The simplest way to create or update a hash value (instance method `[]=`):

    h = {foo: 0, bar: 1, baz: 2}
    h[:bat] = 3 # => 3
    h # => {foo: 0, bar: 1, baz: 2, bat: 3}
    h[:foo] = 4 # => 4
    h # => {foo: 4, bar: 1, baz: 2, bat: 3}

The simplest way to delete a hash entry (instance method `delete`):

    h = {foo: 0, bar: 1, baz: 2}
    h.delete(:bar) # => 1
    h # => {foo: 0, baz: 2}

### Entry Order

A Hash object presents its entries in the order of their creation. This is seen in:

- Iterative methods such as `each`, `each_key`, `each_pair`, `each_value`.

- Other order-sensitive methods such as `shift`, `keys`, `values`.

- The string returned by method `inspect`.

A new hash has its initial ordering per the given entries:

    h = Hash[foo: 0, bar: 1]
    h # => {foo: 0, bar: 1}

New entries are added at the end:

    h[:baz] = 2
    h # => {foo: 0, bar: 1, baz: 2}

Updating a value does not affect the order:

    h[:baz] = 3
    h # => {foo: 0, bar: 1, baz: 3}

But re-creating a deleted entry can affect the order:

    h.delete(:foo)
    h[:foo] = 5
    h # => {bar: 1, baz: 3, foo: 5}

### `Hash` Keys

#### `Hash` Key Equivalence

Two objects are treated as the same hash key when their `hash` value is identical and the two objects are `eql?` to each other.

#### Modifying an Active `Hash` Key

Modifying a `Hash` key while it is in use damages the hash’s index.

This `Hash` has keys that are Arrays:

    a0 = [ :foo, :bar ]
    a1 = [ :baz, :bat ]
    h = {a0 => 0, a1 => 1}
    h.include?(a0) # => true
    h[a0] # => 0
    a0.hash # => 110002110

Modifying array element `a0[0]` changes its hash value:

    a0[0] = :bam
    a0.hash # => 1069447059

And damages the `Hash` index:

    h.include?(a0) # => false
    h[a0] # => nil

You can repair the hash index using method `rehash`:

    h.rehash # => {[:bam, :bar]=>0, [:baz, :bat]=>1}
    h.include?(a0) # => true
    h[a0] # => 0

A `String` key is always safe. That’s because an unfrozen `String` passed as a key will be replaced by a duplicated and frozen String:

    s = 'foo'
    s.frozen? # => false
    h = {s => 0}
    first_key = h.keys.first
    first_key.frozen? # => true

#### User-Defined `Hash` Keys

To be usable as a `Hash` key, objects must implement the methods `hash` and `eql?`. Note: this requirement does not apply if the `Hash` uses `compare_by_identity` since comparison will then rely on the keys’ object id instead of `hash` and `eql?`.

`Object` defines basic implementation for `hash` and `eq?` that makes each object a distinct key. Typically, user-defined classes will want to override these methods to provide meaningful behavior, or for example inherit `Struct` that has useful definitions for these.

A typical implementation of `hash` is based on the object’s data while `eql?` is usually aliased to the overridden `==` method:

    class Book
      attr_reader :author, :title

      def initialize(author, title)
        @author = author
        @title = title
      end

      def ==(other)
        self.class === other &&
          other.author == @author &&
          other.title == @title
      end

      alias eql? ==

      def hash
        [self.class, @author, @title].hash
      end
    end

    book1 = Book.new 'matz', 'Ruby in a Nutshell'
    book2 = Book.new 'matz', 'Ruby in a Nutshell'

    reviews = {}

    reviews[book1] = 'Great reference!'
    reviews[book2] = 'Nice and compact!'

    reviews.length #=> 1

### Key Not Found?

When a method tries to retrieve and return the value for a key and that key is found, the returned value is the value associated with the key.

But what if the key is not found? In that case, certain methods will return a default value while other will raise a KeyError.

#### Nil Return Value

If you want `nil` returned for a not-found key, you can call:

- `[](key)` (usually written as `#[key]`.

- `assoc(key)`.

- `dig(key, *identifiers)`.

- `values_at(*keys)`.

You can override these behaviors for `[]`, `dig`, and `values_at` (but not `assoc`); see Hash Default.

#### KeyError

If you want `KeyError` raised for a not-found key, you can call:

- `fetch(key)`.

- `fetch_values(*keys)`.

#### Hash Default

For certain methods (`[]`, `dig`, and `values_at`), the return value for a not-found key is determined by two hash properties:

- default value: returned by method `default`.

- default proc: returned by method `default_proc`.

In the simple case, both values are `nil`, and the methods return `nil` for a not-found key; see Nil Return Value above.

Note that this entire section (“Hash Default”):

- Applies only to methods `[]`, `dig`, and `values_at`.

- Does not apply to methods `assoc`, `fetch`, or `fetch_values`, which are not affected by the default value or default proc.

##### Any-Key Default

You can define an any-key default for a hash; that is, a value that will be returned for any not-found key:

- The value of `default_proc` must be `nil`.

- The value of `default` (which may be any object, including `nil`) will be returned for a not-found key.

You can set the default value when the hash is created with `Hash.new` and option `default_value`, or later with method `default=`.

Note: although the value of `default` may be any object, it may not be a good idea to use a mutable object.

##### Per-Key Defaults

You can define a per-key default for a hash; that is, a `Proc` that will return a value based on the key itself.

You can set the default proc when the hash is created with `Hash.new` and a block, or later with method `default_proc=`.

Note that the proc can modify `self`, but modifying `self` in this way is not thread-safe; multiple threads can concurrently call into the default proc for the same key.

#### Method Default

For two methods, you can specify a default value for a not-found key that has effect only for a single method call (and not for any subsequent calls):

- For method `fetch`, you can specify an any-key default:

- For either method `fetch` or method `fetch_values`, you can specify a per-key default via a block.

### What’s Here

First, what’s elsewhere. Class `Hash`:

- Inherits from class Object.

- Includes module Enumerable, which provides dozens of additional methods.

Here, class `Hash` provides methods that are useful for:

- Creating a Hash

- Setting Hash State

- Querying

- Comparing

- Fetching

- Assigning

- Deleting

- Iterating

- Converting

- Transforming Keys and Values

Class `Hash` also includes methods from module `Enumerable`.

#### Methods for Creating a `Hash`

- `::[]`: Returns a new hash populated with given objects.

- `::new`: Returns a new empty hash.

- `::try_convert`: Returns a new hash created from a given object.

#### Methods for Setting `Hash` State

- `compare_by_identity`: Sets `self` to consider only identity in comparing keys.

- `default=`: Sets the default to a given value.

- `default_proc=`: Sets the default proc to a given proc.

- `rehash`: Rebuilds the hash table by recomputing the hash index for each key.

#### Methods for Querying

- `any?`: Returns whether any element satisfies a given criterion.

- `compare_by_identity?`: Returns whether the hash considers only identity when comparing keys.

- `default`: Returns the default value, or the default value for a given key.

- `default_proc`: Returns the default proc.

- `empty?`: Returns whether there are no entries.

- `eql?`: Returns whether a given object is equal to `self`.

- `hash`: Returns the integer hash code.

- `has_value?` (aliased as `value?`): Returns whether a given object is a value in `self`.

- `include?` (aliased as `has_key?`, `member?`, `key?`): Returns whether a given object is a key in `self`.

- `size` (aliased as `length`): Returns the count of entries.

#### Methods for Comparing

- `<`: Returns whether `self` is a proper subset of a given object.

- `<=`: Returns whether `self` is a subset of a given object.

- `==`: Returns whether a given object is equal to `self`.

- `>`: Returns whether `self` is a proper superset of a given object

- `>=`: Returns whether `self` is a superset of a given object.

#### Methods for Fetching

- `[]`: Returns the value associated with a given key.

- `assoc`: Returns a 2-element array containing a given key and its value.

- `dig`: Returns the object in nested objects that is specified by a given key and additional arguments.

- `fetch`: Returns the value for a given key.

- `fetch_values`: Returns array containing the values associated with given keys.

- `key`: Returns the key for the first-found entry with a given value.

- `keys`: Returns an array containing all keys in `self`.

- `rassoc`: Returns a 2-element array consisting of the key and value of the first-found entry having a given value.

- `values`: Returns an array containing all values in `self`.

- `values_at`: Returns an array containing values for given keys.

#### Methods for Assigning

- `[]=` (aliased as `store`): Associates a given key with a given value.

- `merge`: Returns the hash formed by merging each given hash into a copy of `self`.

- `update` (aliased as `merge!`): Merges each given hash into `self`.

- `replace` (aliased as `initialize_copy`): Replaces the entire contents of `self` with the contents of a given hash.

#### Methods for Deleting

These methods remove entries from `self`:

- `clear`: Removes all entries from `self`.

- `compact!`: Removes all `nil`-valued entries from `self`.

- `delete`: Removes the entry for a given key.

- `delete_if`: Removes entries selected by a given block.

- `select!` (aliased as `filter!`): Keep only those entries selected by a given block.

- `keep_if`: Keep only those entries selected by a given block.

- `reject!`: Removes entries selected by a given block.

- `shift`: Removes and returns the first entry.

These methods return a copy of `self` with some entries removed:

- `compact`: Returns a copy of `self` with all `nil`-valued entries removed.

- `except`: Returns a copy of `self` with entries removed for specified keys.

- `select` (aliased as `filter`): Returns a copy of `self` with only those entries selected by a given block.

- `reject`: Returns a copy of `self` with entries removed as specified by a given block.

- `slice`: Returns a hash containing the entries for given keys.

#### Methods for Iterating

- `each_pair` (aliased as `each`): Calls a given block with each key-value pair.

- `each_key`: Calls a given block with each key.

- `each_value`: Calls a given block with each value.

#### Methods for Converting

- `flatten`: Returns an array that is a 1-dimensional flattening of `self`.

- `inspect` (aliased as `to_s`): Returns a new `String` containing the hash entries.

- `to_a`: Returns a new array of 2-element arrays; each nested array contains a key-value pair from `self`.

- `to_h`: Returns `self` if a `Hash`; if a subclass of `Hash`, returns a `Hash` containing the entries from `self`.

- `to_hash`: Returns `self`.

- `to_proc`: Returns a proc that maps a given key to its value.

#### Methods for Transforming Keys and Values

- `invert`: Returns a hash with the each key-value pair inverted.

- `transform_keys`: Returns a copy of `self` with modified keys.

- `transform_keys!`: Modifies keys in `self`

- `transform_values`: Returns a copy of `self` with modified values.

- `transform_values!`: Modifies values in `self`.

### Public Class Methods

Hash[] → new_empty_hash
Hash[other_hash] → new_hash
Hash[ [*2_element_arrays] ] → new_hash
Hash[*objects] → new_hash
Source

    static VALUE
    rb_hash_s_create(int argc, VALUE *argv, VALUE klass)
    {
        VALUE hash, tmp;

        if (argc == 1) {
            tmp = rb_hash_s_try_convert(Qnil, argv[0]);
            if (!NIL_P(tmp)) {
                if (!RHASH_EMPTY_P(tmp)  && rb_hash_compare_by_id_p(tmp)) {
                    /* hash_copy for non-empty hash will copy compare_by_identity
                       flag, but we don't want it copied. Work around by
                       converting hash to flattened array and using that. */
                    tmp = rb_hash_to_a(tmp);
                }
                else {
                    hash = hash_alloc(klass);
                    if (!RHASH_EMPTY_P(tmp))
                        hash_copy(hash, tmp);
                    return hash;
                }
            }
            else {
                tmp = rb_check_array_type(argv[0]);
            }

            if (!NIL_P(tmp)) {
                long i;

                hash = hash_alloc(klass);
                for (i = 0; i < RARRAY_LEN(tmp); ++i) {
                    VALUE e = RARRAY_AREF(tmp, i);
                    VALUE v = rb_check_array_type(e);
                    VALUE key, val = Qnil;

                    if (NIL_P(v)) {
                        rb_raise(rb_eArgError, "wrong element type %s at %ld (expected array)",
                                 rb_builtin_class_name(e), i);
                    }
                    switch (RARRAY_LEN(v)) {
                      default:
                        rb_raise(rb_eArgError, "invalid number of elements (%ld for 1..2)",
                                 RARRAY_LEN(v));
                      case 2:
                        val = RARRAY_AREF(v, 1);
                      case 1:
                        key = RARRAY_AREF(v, 0);
                        rb_hash_aset(hash, key, val);
                    }
                }
                return hash;
            }
        }
        if (argc % 2 != 0) {
            rb_raise(rb_eArgError, "odd number of arguments for Hash");
        }

        hash = hash_alloc(klass);
        rb_hash_bulk_insert(argc, argv, hash);
        hash_verify(hash);
        return hash;
    }

Returns a new Hash object populated with the given objects, if any. See `Hash::new`.

With no argument given, returns a new empty hash.

With a single argument `other_hash` given that is a hash, returns a new hash initialized with the entries from that hash (but not with its `default` or `default_proc`):

    h = {foo: 0, bar: 1, baz: 2}
    Hash[h] # => {foo: 0, bar: 1, baz: 2}

With a single argument `2_element_arrays` given that is an array of 2-element arrays, returns a new hash wherein each given 2-element array forms a key-value entry:

    Hash[ [ [:foo, 0], [:bar, 1] ] ] # => {foo: 0, bar: 1}

With an even number of arguments `objects` given, returns a new hash wherein each successive pair of arguments is a key-value entry:

    Hash[:foo, 0, :bar, 1] # => {foo: 0, bar: 1}

Raises `ArgumentError` if the argument list does not conform to any of the above.

See also Methods for Creating a Hash.

new(default_value = nil, capacity: 0) → new_hash
new(capacity: 0) {|self, key| ... } → new_hash
Source

    # File hash.rb, line 37
    def initialize(ifnone = (ifnone_unset = true), capacity: 0, &block)
      Primitive.rb_hash_init(capacity, ifnone_unset, ifnone, block)
    end

Returns a new empty Hash object.

Initializes the values of `Hash#default` and `Hash#default_proc`, which determine the behavior when a given key is not found; see Key Not Found?.

By default, a hash has `nil` values for both `default` and `default_proc`:

    h = Hash.new        # => {}
    h.default           # => nil
    h.default_proc      # => nil

With argument `default_value` given, sets the `default` value for the hash:

    h = Hash.new(false) # => {}
    h.default           # => false
    h.default_proc      # => nil

With a block given, sets the `default_proc` value:

    h = Hash.new {|hash, key| "Hash #{hash}: Default value for #{key}" }
    h.default      # => nil
    h.default_proc # => #<Proc:0x00000289b6fa7048 (irb):185>
    h[:nosuch]     # => "Hash {}: Default value for nosuch"

Raises `ArgumentError` if both `default_value` and a block are given.

If optional keyword argument `capacity` is given with a positive integer value `n`, initializes the hash with enough capacity to accommodate `n` entries without resizing.

See also Methods for Creating a Hash.

ruby2_keywords_hash(hash) → hash
Source

    static VALUE
    rb_hash_s_ruby2_keywords_hash(VALUE dummy, VALUE hash)
    {
        Check_Type(hash, T_HASH);
        VALUE tmp = rb_hash_dup(hash);
        if (RHASH_EMPTY_P(hash) && rb_hash_compare_by_id_p(hash)) {
            rb_hash_compare_by_id(tmp);
        }
        RHASH(tmp)->basic.flags |= RHASH_PASS_AS_KEYWORDS;
        return tmp;
    }

Duplicates a given hash and adds a ruby2_keywords flag. This method is not for casual use; debugging, researching, and some truly necessary cases like deserialization of arguments.

    h = {k: 1}
    h = Hash.ruby2_keywords_hash(h)
    def foo(k: 42)
      k
    end
    foo(*[h]) #=> 1 with neither a warning or an error

ruby2_keywords_hash?(hash) → true or false
Source

    static VALUE
    rb_hash_s_ruby2_keywords_hash_p(VALUE dummy, VALUE hash)
    {
        Check_Type(hash, T_HASH);
        return RBOOL(RHASH(hash)->basic.flags & RHASH_PASS_AS_KEYWORDS);
    }

Checks if a given hash is flagged by `Module#ruby2_keywords` (or `Proc#ruby2_keywords`). This method is not for casual use; debugging, researching, and some truly necessary cases like serialization of arguments.

    ruby2_keywords def foo(*args)
      Hash.ruby2_keywords_hash?(args.last)
    end
    foo(k: 1)   #=> true
    foo({k: 1}) #=> false

try_convert(object) → object, new_hash, or nil
Source

    static VALUE
    rb_hash_s_try_convert(VALUE dummy, VALUE hash)
    {
        return rb_check_hash_type(hash);
    }

If `object` is a hash, returns `object`.

Otherwise if `object` responds to `:to_hash`, calls `object.to_hash`; returns the result if it is a hash, or raises `TypeError` if not.

Otherwise if `object` does not respond to `:to_hash`, returns `nil`.

### Public Instance Methods

self < other → true or false
Source

    static VALUE
    rb_hash_lt(VALUE hash, VALUE other)
    {
        other = to_hash(other);
        if (RHASH_SIZE(hash) >= RHASH_SIZE(other)) return Qfalse;
        return hash_le(hash, other);
    }

Returns whether the entries of `self` are a proper subset of the entries of `other`:

    h = {foo: 0, bar: 1}
    h < {foo: 0, bar: 1, baz: 2} # => true   # Proper subset.
    h < {baz: 2, bar: 1, foo: 0} # => true   # Order may differ.
    h < h                        # => false  # Not a proper subset.
    h < {bar: 1, foo: 0}         # => false  # Not a proper subset.
    h < {foo: 0, bar: 1, baz: 2} # => false  # Different key.
    h < {foo: 0, bar: 1, baz: 2} # => false  # Different value.

See Hash Inclusion.

Raises `TypeError` if `other_hash` is not a hash and cannot be converted to a hash.

Related: see Methods for Comparing.

self <= other → true or false
Source

    static VALUE
    rb_hash_le(VALUE hash, VALUE other)
    {
        other = to_hash(other);
        if (RHASH_SIZE(hash) > RHASH_SIZE(other)) return Qfalse;
        return hash_le(hash, other);
    }

Returns whether the entries of `self` are a subset of the entries of `other`:

    h0 = {foo: 0, bar: 1}
    h1 = {foo: 0, bar: 1, baz: 2}
    h0 <= h0 # => true
    h0 <= h1 # => true
    h1 <= h0 # => false

See Hash Inclusion.

Raises `TypeError` if `other_hash` is not a hash and cannot be converted to a hash.

Related: see Methods for Comparing.

self == object → true or false
Source

    static VALUE
    rb_hash_equal(VALUE hash1, VALUE hash2)
    {
        return hash_equal(hash1, hash2, FALSE);
    }

Returns whether `self` and `object` are equal.

Returns `true` if all of the following are true:

- `object` is a `Hash` object (or can be converted to one).

- `self` and `object` have the same keys (regardless of order).

- For each key `key`, `self[key] == object[key]`.

Otherwise, returns `false`.

Examples:

    h =  {foo: 0, bar: 1}
    h == {foo: 0, bar: 1} # => true   # Equal entries (same order)
    h == {bar: 1, foo: 0} # => true   # Equal entries (different order).
    h == 1                            # => false  # Object not a hash.
    h == {}                           # => false  # Different number of entries.
    h == {foo: 0, bar: 1} # => false  # Different key.
    h == {foo: 0, bar: 1} # => false  # Different value.

Related: see Methods for Comparing.

self > other_hash → true or false
Source

    static VALUE
    rb_hash_gt(VALUE hash, VALUE other)
    {
        other = to_hash(other);
        if (RHASH_SIZE(hash) <= RHASH_SIZE(other)) return Qfalse;
        return hash_le(other, hash);
    }

Returns `true` if the entries of `self` are a proper superset of the entries of `other_hash`, `false` otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h > {foo: 0, bar: 1}         # => true   # Proper superset.
    h > {bar: 1, foo: 0}         # => true   # Order may differ.
    h > h                        # => false  # Not a proper superset.
    h > {baz: 2, bar: 1, foo: 0} # => false  # Not a proper superset.
    h > {foo: 0, bar: 1}         # => false  # Different key.
    h > {foo: 0, bar: 1}         # => false  # Different value.

See Hash Inclusion.

Raises `TypeError` if `other_hash` is not a hash and cannot be converted to a hash.

Related: see Methods for Comparing.

self >= other_hash → true or false
Source

    static VALUE
    rb_hash_ge(VALUE hash, VALUE other)
    {
        other = to_hash(other);
        if (RHASH_SIZE(hash) < RHASH_SIZE(other)) return Qfalse;
        return hash_le(other, hash);
    }

Returns `true` if the entries of `self` are a superset of the entries of `other_hash`, `false` otherwise:

    h0 = {foo: 0, bar: 1, baz: 2}
    h1 = {foo: 0, bar: 1}
    h0 >= h1 # => true
    h0 >= h0 # => true
    h1 >= h0 # => false

See Hash Inclusion.

Raises `TypeError` if `other_hash` is not a hash and cannot be converted to a hash.

Related: see Methods for Comparing.

self[key] → object
Source

    VALUE
    rb_hash_aref(VALUE hash, VALUE key)
    {
        st_data_t val;

        if (hash_stlike_lookup(hash, key, &val)) {
            return (VALUE)val;
        }
        else {
            return rb_hash_default_value(hash, key);
        }
    }

Searches for a hash key equivalent to the given `key`; see Hash Key Equivalence.

If the key is found, returns its value:

    {foo: 0, bar: 1, baz: 2}
    h[:bar] # => 1

Otherwise, returns a default value (see Hash Default).

Related: `[]=`; see also Methods for Fetching.

self[key] = object → object
Source

    VALUE
    rb_hash_aset(VALUE hash, VALUE key, VALUE val)
    {
        bool iter_p = hash_iterating_p(hash);

        rb_hash_modify(hash);

        if (!RHASH_STRING_KEY_P(hash, key)) {
            RHASH_UPDATE_ITER(hash, iter_p, key, hash_aset, val);
        }
        else {
            RHASH_UPDATE_ITER(hash, iter_p, key, hash_aset_str, val);
        }
        return val;
    }

Associates the given `object` with the given `key`; returns `object`.

Searches for a hash key equivalent to the given `key`; see Hash Key Equivalence.

If the key is found, replaces its value with the given `object`; the ordering is not affected (see Entry Order):

    h = {foo: 0, bar: 1}
    h[:foo] = 2 # => 2
    h[:foo]     # => 2

If `key` is not found, creates a new entry for the given `key` and `object`; the new entry is last in the order (see Entry Order):

    h = {foo: 0, bar: 1}
    h[:baz] = 2 # => 2
    h[:baz]     # => 2
    h           # => {:foo=>0, :bar=>1, :baz=>2}

Related: `[]`; see also Methods for Assigning.

Also aliased as: store
any? → true or false
any?(entry) → true or false
any? {|key, value| ... } → true or false
Source

    static VALUE
    rb_hash_any_p(int argc, VALUE *argv, VALUE hash)
    {
        VALUE args[2];
        args[0] = Qfalse;

        rb_check_arity(argc, 0, 1);
        if (RHASH_EMPTY_P(hash)) return Qfalse;
        if (argc) {
            if (rb_block_given_p()) {
                rb_warn("given block not used");
            }
            args[1] = argv[0];

            rb_hash_foreach(hash, any_p_i_pattern, (VALUE)args);
        }
        else {
            if (!rb_block_given_p()) {
                /* yields pairs, never false */
                return Qtrue;
            }
            if (rb_block_pair_yield_optimizable())
                rb_hash_foreach(hash, any_p_i_fast, (VALUE)args);
            else
                rb_hash_foreach(hash, any_p_i, (VALUE)args);
        }
        return args[0];
    }

Returns `true` if any element satisfies a given criterion; `false` otherwise.

If `self` has no element, returns `false` and argument or block are not used; otherwise behaves as below.

With no argument and no block, returns `true` if `self` is non-empty, `false` otherwise.

With argument `entry` and no block, returns `true` if for any key `key` `self.assoc(key) == entry`, `false` otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h.assoc(:bar)     # => [:bar, 1]
    h.any?([:bar, 1]) # => true
    h.any?([:bar, 0]) # => false

With no argument and a block given, calls the block with each key-value pair; returns `true` if the block returns a truthy value, `false` otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h.any? {|key, value| value < 3 } # => true
    h.any? {|key, value| value > 3 } # => false

With both argument `entry` and a block given, issues a warning and ignores the block.

Related: `Enumerable#any?` (which this method overrides); see also Methods for Fetching.

assoc(key) → entry or nil
Source

    static VALUE
    rb_hash_assoc(VALUE hash, VALUE key)
    {
        VALUE args[2];

        if (RHASH_EMPTY_P(hash)) return Qnil;

        if (RHASH_ST_TABLE_P(hash) && !RHASH_IDENTHASH_P(hash)) {
            VALUE value = Qundef;
            st_table assoctable = *RHASH_ST_TABLE(hash);
            assoctable.type = &(struct st_hash_type){
                .compare = assoc_cmp,
                .hash = assoctable.type->hash,
            };
            VALUE arg = (VALUE)&(struct assoc_arg){
                .tbl = &assoctable,
                .key = (st_data_t)key,
            };

            if (RB_OBJ_FROZEN(hash)) {
                value = assoc_lookup(arg);
            }
            else {
                hash_iter_lev_inc(hash);
                value = rb_ensure(assoc_lookup, arg, hash_foreach_ensure, hash);
            }
            hash_verify(hash);
            if (!UNDEF_P(value)) return rb_assoc_new(key, value);
        }

        args[0] = key;
        args[1] = Qnil;
        rb_hash_foreach(hash, assoc_i, (VALUE)args);
        return args[1];
    }

If the given `key` is found, returns its entry as a 2-element array containing that key and its value:

    h = {foo: 0, bar: 1, baz: 2}
    h.assoc(:bar) # => [:bar, 1]

Returns `nil` if the key is not found.

Related: see Methods for Fetching.

clear → self
Source

    VALUE
    rb_hash_clear(VALUE hash)
    {
        rb_hash_modify_check(hash);

        if (hash_iterating_p(hash)) {
            rb_hash_foreach(hash, clear_i, 0);
        }
        else if (RHASH_AR_TABLE_P(hash)) {
            ar_clear(hash);
        }
        else {
            st_clear(RHASH_ST_TABLE(hash));
            compact_after_delete(hash);
        }

        return hash;
    }

Removes all entries from `self`; returns emptied `self`.

Related: see Methods for Deleting.

compact → new_hash
Source

    static VALUE
    rb_hash_compact(VALUE hash)
    {
        VALUE result = rb_hash_dup(hash);
        if (!RHASH_EMPTY_P(hash)) {
            rb_hash_foreach(result, delete_if_nil, result);
            compact_after_delete(result);
        }
        else if (rb_hash_compare_by_id_p(hash)) {
            result = rb_hash_compare_by_id(result);
        }
        return result;
    }

Returns a copy of `self` with all `nil`-valued entries removed:

    h = {foo: 0, bar: nil, baz: 2, bat: nil}
    h.compact # => {foo: 0, baz: 2}

Related: see Methods for Deleting.

compact! → self or nil
Source

    static VALUE
    rb_hash_compact_bang(VALUE hash)
    {
        st_index_t n;
        rb_hash_modify_check(hash);
        n = RHASH_SIZE(hash);
        if (n) {
            rb_hash_foreach(hash, delete_if_nil, hash);
            if (n != RHASH_SIZE(hash))
                return hash;
        }
        return Qnil;
    }

If `self` contains any `nil`-valued entries, returns `self` with all `nil`-valued entries removed; returns `nil` otherwise:

    h = {foo: 0, bar: nil, baz: 2, bat: nil}
    h.compact!
    h          # => {foo: 0, baz: 2}
    h.compact! # => nil

Related: see Methods for Deleting.

compare_by_identity → self
Source

    VALUE
    rb_hash_compare_by_id(VALUE hash)
    {
        VALUE tmp;
        st_table *identtable;

        if (rb_hash_compare_by_id_p(hash)) return hash;

        rb_hash_modify_check(hash);
        if (hash_iterating_p(hash)) {
            rb_raise(rb_eRuntimeError, "compare_by_identity during iteration");
        }

        if (RHASH_TABLE_EMPTY_P(hash)) {
            // Fast path: There's nothing to rehash, so we don't need a `tmp` table.
            // We're most likely an AR table, so this will need an allocation.
            ar_force_convert_table(hash, __FILE__, __LINE__);
            HASH_ASSERT(RHASH_ST_TABLE_P(hash));

            RHASH_ST_TABLE(hash)->type = &identhash;
        }
        else {
            // Slow path: Need to rehash the members of `self` into a new
            // `tmp` table using the new `identhash` compare/hash functions.
            tmp = hash_alloc(0);
            hash_st_table_init(tmp, &identhash, RHASH_SIZE(hash));
            identtable = RHASH_ST_TABLE(tmp);

            rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);
            rb_hash_free(hash);

            // We know for sure `identtable` is an st table,
            // so we can skip `ar_force_convert_table` here.
            RHASH_ST_TABLE_SET(hash, identtable);
            RHASH_ST_CLEAR(tmp);
        }

        return hash;
    }

Sets `self` to compare keys using identity (rather than mere equality); returns `self`:

By default, two keys are considered to be the same key if and only if they are equal objects (per method `eql?`):

    h = {}
    h['x'] = 0
    h['x'] = 1 # Overwrites.
    h # => {"x"=>1}

When this method has been called, two keys are considered to be the same key if and only if they are the same object:

    h.compare_by_identity
    h['x'] = 2 # Does not overwrite.
    h # => {"x"=>1, "x"=>2}

Related: `compare_by_identity?`; see also Methods for Comparing.

compare_by_identity? → true or false
Source

    VALUE
    rb_hash_compare_by_id_p(VALUE hash)
    {
        return RBOOL(RHASH_IDENTHASH_P(hash));
    }

Returns whether `compare_by_identity` has been called:

    h = {}
    h.compare_by_identity? # => false
    h.compare_by_identity
    h.compare_by_identity? # => true

Related: `compare_by_identity`; see also Methods for Comparing.

default → object
default(key) → object
Source

    static VALUE
    rb_hash_default(int argc, VALUE *argv, VALUE hash)
    {
        VALUE ifnone;

        rb_check_arity(argc, 0, 1);
        ifnone = RHASH_IFNONE(hash);
        if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
            if (argc == 0) return Qnil;
            return call_default_proc(ifnone, hash, argv[0]);
        }
        return ifnone;
    }

Returns the default value for the given `key`. The returned value will be determined either by the default proc or by the default value. See Hash Default.

With no argument, returns the current default value:

    h = {}
    h.default # => nil

If `key` is given, returns the default value for `key`, regardless of whether that key exists:

    h = Hash.new { |hash, key| hash[key] = "No key #{key}"}
    h[:foo] = "Hello"
    h.default(:foo) # => "No key foo"

default = value → object
Source

    VALUE
    rb_hash_set_default(VALUE hash, VALUE ifnone)
    {
        rb_hash_modify_check(hash);
        SET_DEFAULT(hash, ifnone);
        return ifnone;
    }

Sets the default value to `value`; returns `value`:

    h = {}
    h.default # => nil
    h.default = false # => false
    h.default # => false

See Hash Default.

default_proc → proc or nil
Source

    static VALUE
    rb_hash_default_proc(VALUE hash)
    {
        if (FL_TEST(hash, RHASH_PROC_DEFAULT)) {
            return RHASH_IFNONE(hash);
        }
        return Qnil;
    }

Returns the default proc for `self` (see Hash Default):

    h = {}
    h.default_proc # => nil
    h.default_proc = proc {|hash, key| "Default value for #{key}" }
    h.default_proc.class # => Proc

default_proc = proc → proc
Source

    VALUE
    rb_hash_set_default_proc(VALUE hash, VALUE proc)
    {
        VALUE b;

        rb_hash_modify_check(hash);
        if (NIL_P(proc)) {
            SET_DEFAULT(hash, proc);
            return proc;
        }
        b = rb_check_convert_type_with_id(proc, T_DATA, "Proc", idTo_proc);
        if (NIL_P(b) || !rb_obj_is_proc(b)) {
            rb_raise(rb_eTypeError,
                     "wrong default_proc type %s (expected Proc)",
                     rb_obj_classname(proc));
        }
        proc = b;
        SET_PROC_DEFAULT(hash, proc);
        return proc;
    }

Sets the default proc for `self` to `proc` (see Hash Default):

    h = {}
    h.default_proc # => nil
    h.default_proc = proc { |hash, key| "Default value for #{key}" }
    h.default_proc.class # => Proc
    h.default_proc = nil
    h.default_proc # => nil

delete(key) → value or nil
delete(key) {|key| ... } → object
Source

    static VALUE
    rb_hash_delete_m(VALUE hash, VALUE key)
    {
        VALUE val;

        rb_hash_modify_check(hash);
        val = rb_hash_delete_entry(hash, key);

        if (!UNDEF_P(val)) {
            compact_after_delete(hash);
            return val;
        }
        else {
            if (rb_block_given_p()) {
                return rb_yield(key);
            }
            else {
                return Qnil;
            }
        }
    }

If an entry for the given `key` is found, deletes the entry and returns its associated value; otherwise returns `nil` or calls the given block.

With no block given and `key` found, deletes the entry and returns its value:

    h = {foo: 0, bar: 1, baz: 2}
    h.delete(:bar) # => 1
    h # => {foo: 0, baz: 2}

With no block given and `key` not found, returns `nil`.

With a block given and `key` found, ignores the block, deletes the entry, and returns its value:

    h = {foo: 0, bar: 1, baz: 2}
    h.delete(:baz) { |key| raise 'Will never happen'} # => 2
    h # => {foo: 0, bar: 1}

With a block given and `key` not found, calls the block and returns the block’s return value:

    h = {foo: 0, bar: 1, baz: 2}
    h.delete(:nosuch) { |key| "Key #{key} not found" } # => "Key nosuch not found"
    h # => {foo: 0, bar: 1, baz: 2}

Related: see Methods for Deleting.

delete_if {|key, value| ... } → self
delete_if → new_enumerator
Source

    VALUE
    rb_hash_delete_if(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_modify_check(hash);
        if (!RHASH_TABLE_EMPTY_P(hash)) {
            rb_hash_foreach(hash, delete_if_i, hash);
            compact_after_delete(hash);
        }
        return hash;
    }

With a block given, calls the block with each key-value pair, deletes each entry for which the block returns a truthy value, and returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.delete_if {|key, value| value > 0 } # => {foo: 0}

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

dig(key, *identifiers) → object
Source

    static VALUE
    rb_hash_dig(int argc, VALUE *argv, VALUE self)
    {
        rb_check_arity(argc, 1, UNLIMITED_ARGUMENTS);
        self = rb_hash_aref(self, *argv);
        if (!--argc) return self;
        ++argv;
        return rb_obj_dig(argc, argv, self, Qnil);
    }

Finds and returns an object found in nested objects, as specified by `key` and `identifiers`.

The nested objects may be instances of various classes. See Dig Methods.

Nested hashes:

    h = {foo: {bar: {baz: 2}}}
    h.dig(:foo) # => {bar: {baz: 2}}
    h.dig(:foo, :bar) # => {baz: 2}
    h.dig(:foo, :bar, :baz) # => 2
    h.dig(:foo, :bar, :BAZ) # => nil

Nested hashes and arrays:

    h = {foo: {bar: [:a, :b, :c]}}
    h.dig(:foo, :bar, 2) # => :c

If no such object is found, returns the hash default:

    h = {foo: {bar: [:a, :b, :c]}}
    h.dig(:hello) # => nil
    h.default_proc = -> (hash, _key) { hash }
    h.dig(:hello, :world)
    # => {:foo=>{:bar=>[:a, :b, :c]}}

Related: Methods for Fetching.

each
Alias for: each_pair
each_key {|key| ... } → self
each_key → new_enumerator
Source

    static VALUE
    rb_hash_each_key(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_foreach(hash, each_key_i, 0);
        return hash;
    }

With a block given, calls the block with each key; returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.each_key {|key| puts key }  # => {foo: 0, bar: 1, baz: 2}

Output:

    foo
    bar
    baz

With no block given, returns a new `Enumerator`.

Related: see Methods for Iterating.

each_pair {|key, value| ... } → self
each_pair → new_enumerator
Source

    static VALUE
    rb_hash_each_pair(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        if (rb_block_pair_yield_optimizable())
            rb_hash_foreach(hash, each_pair_i_fast, 0);
        else
            rb_hash_foreach(hash, each_pair_i, 0);
        return hash;
    }

With a block given, calls the block with each key-value pair; returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.each_pair {|key, value| puts "#{key}: #{value}"} # => {foo: 0, bar: 1, baz: 2}

Output:

    foo: 0
    bar: 1
    baz: 2

With no block given, returns a new `Enumerator`.

Related: see Methods for Iterating.

Also aliased as: each
each_value {|value| ... } → self
each_value → new_enumerator
Source

    static VALUE
    rb_hash_each_value(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_foreach(hash, each_value_i, 0);
        return hash;
    }

With a block given, calls the block with each value; returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.each_value {|value| puts value } # => {foo: 0, bar: 1, baz: 2}

Output:

    0
    1
    2

With no block given, returns a new `Enumerator`.

Related: see Methods for Iterating.

empty? → true or false
Source

    VALUE
    rb_hash_empty_p(VALUE hash)
    {
        return RBOOL(RHASH_EMPTY_P(hash));
    }

Returns `true` if there are no hash entries, `false` otherwise:

    {}.empty? # => true
    {foo: 0}.empty? # => false

Related: see Methods for Querying.

eql?(object) → true or false
Source

    static VALUE
    rb_hash_eql(VALUE hash1, VALUE hash2)
    {
        return hash_equal(hash1, hash2, TRUE);
    }

Returns `true` if all of the following are true:

- The given `object` is a `Hash` object.

- `self` and `object` have the same keys (regardless of order).

- For each key `key`, `self[key].eql?(object[key])`.

Otherwise, returns `false`.

    h1 = {foo: 0, bar: 1, baz: 2}
    h2 = {foo: 0, bar: 1, baz: 2}
    h1.eql? h2 # => true
    h3 = {baz: 2, bar: 1, foo: 0}
    h1.eql? h3 # => true

Related: see Methods for Querying.

except(*keys) → new_hash
Source

    static VALUE
    rb_hash_except(int argc, VALUE *argv, VALUE hash)
    {
        int i;
        VALUE key, result;

        result = hash_dup_with_compare_by_id(hash);

        for (i = 0; i < argc; i++) {
            key = argv[i];
            rb_hash_delete(result, key);
        }
        compact_after_delete(result);

        return result;
    }

Returns a copy of `self` that excludes entries for the given `keys`; any `keys` that are not found are ignored:

    h = {foo:0, bar: 1, baz: 2} # => {:foo=>0, :bar=>1, :baz=>2}
    h.except(:baz, :foo)        # => {:bar=>1}
    h.except(:bar, :nosuch)     # => {:foo=>0, :baz=>2}

Related: see Methods for Deleting.

fetch(key) → object
fetch(key, default_value) → object
fetch(key) {|key| ... } → object
Source

    static VALUE
    rb_hash_fetch_m(int argc, VALUE *argv, VALUE hash)
    {
        VALUE key;
        st_data_t val;
        long block_given;

        rb_check_arity(argc, 1, 2);
        key = argv[0];

        block_given = rb_block_given_p();
        if (block_given && argc == 2) {
            rb_warn("block supersedes default value argument");
        }

        if (hash_stlike_lookup(hash, key, &val)) {
            return (VALUE)val;
        }
        else {
            if (block_given) {
                return rb_yield(key);
            }
            else if (argc == 1) {
                VALUE desc = rb_protect(rb_inspect, key, 0);
                if (NIL_P(desc)) {
                    desc = rb_any_to_s(key);
                }
                desc = rb_str_ellipsize(desc, 65);
                rb_key_err_raise(rb_sprintf("key not found: %"PRIsVALUE, desc), hash, key);
            }
            else {
                return argv[1];
            }
        }
    }

With no block given, returns the value for the given `key`, if found;

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch(:bar)  # => 1

If the key is not found, returns `default_value`, if given, or raises `KeyError` otherwise:

    h.fetch(:nosuch, :default) # => :default
    h.fetch(:nosuch)           # Raises KeyError.

With a block given, calls the block with `key` and returns the block’s return value:

    {}.fetch(:nosuch) {|key| "No key #{key}"} # => "No key nosuch"

Note that this method does not use the values of either `default` or `default_proc`.

Related: see Methods for Fetching.

fetch_values(*keys) → new_array
fetch_values(*keys) {|key| ... } → new_array
Source

    static VALUE
    rb_hash_fetch_values(int argc, VALUE *argv, VALUE hash)
    {
        VALUE result = rb_ary_new2(argc);
        long i;

        for (i=0; i<argc; i++) {
            rb_ary_push(result, rb_hash_fetch(hash, argv[i]));
        }
        return result;
    }

When all given `keys` are found, returns a new array containing the values associated with the given `keys`:

    h = {foo: 0, bar: 1, baz: 2}
    h.fetch_values(:baz, :foo) # => [2, 0]

When any given `keys` are not found and a block is given, calls the block with each unfound key and uses the block’s return value as the value for that key:

    h.fetch_values(:bar, :foo, :bad, :bam) {|key| key.to_s}
    # => [1, 0, "bad", "bam"]

When any given `keys` are not found and no block is given, raises `KeyError`.

Related: see Methods for Fetching.

filter
Alias for: select
filter!
Alias for: select!
flatten(depth = 1) → new_array
Source

    static VALUE
    rb_hash_flatten(int argc, VALUE *argv, VALUE hash)
    {
        VALUE ary;

        rb_check_arity(argc, 0, 1);

        if (argc) {
            int level = NUM2INT(argv[0]);

            if (level == 0) return rb_hash_to_a(hash);

            ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
            rb_hash_foreach(hash, flatten_i, ary);
            level--;

            if (level > 0) {
                VALUE ary_flatten_level = INT2FIX(level);
                rb_funcallv(ary, id_flatten_bang, 1, &ary_flatten_level);
            }
            else if (level < 0) {
                /* flatten recursively */
                rb_funcallv(ary, id_flatten_bang, 0, 0);
            }
        }
        else {
            ary = rb_ary_new_capa(RHASH_SIZE(hash) * 2);
            rb_hash_foreach(hash, flatten_i, ary);
        }

        return ary;
    }

With positive integer `depth`, returns a new array that is a recursive flattening of `self` to the given `depth`.

At each level of recursion:

- Each element whose value is an array is “flattened” (that is, replaced by its individual array elements); see `Array#flatten`.

- Each element whose value is not an array is unchanged. even if the value is an object that has instance method flatten (such as a hash).

Examples; note that entry `foo: {bar: 1, baz: 2}` is never flattened.

    h = {foo: {bar: 1, baz: 2}, bat: [:bam, [:bap, [:bah]]]}
    h.flatten(1) # => [:foo, {:bar=>1, :baz=>2}, :bat, [:bam, [:bap, [:bah]]]]
    h.flatten(2) # => [:foo, {:bar=>1, :baz=>2}, :bat, :bam, [:bap, [:bah]]]
    h.flatten(3) # => [:foo, {:bar=>1, :baz=>2}, :bat, :bam, :bap, [:bah]]
    h.flatten(4) # => [:foo, {:bar=>1, :baz=>2}, :bat, :bam, :bap, :bah]
    h.flatten(5) # => [:foo, {:bar=>1, :baz=>2}, :bat, :bam, :bap, :bah]

With negative integer `depth`, flattens all levels:

    h.flatten(-1) # => [:foo, {:bar=>1, :baz=>2}, :bat, :bam, :bap, :bah]

With `depth` zero, returns the equivalent of `to_a`:

    h.flatten(0) # => [[:foo, {:bar=>1, :baz=>2}], [:bat, [:bam, [:bap, [:bah]]]]]

Related: see Methods for Converting.

has_key?
Alias for: include?
has_value?(value) → true or false
Source

    static VALUE
    rb_hash_has_value(VALUE hash, VALUE val)
    {
        VALUE data[2];

        data[0] = Qfalse;
        data[1] = val;
        rb_hash_foreach(hash, rb_hash_search_value, (VALUE)data);
        return data[0];
    }

Returns whether `value` is a value in `self`.

Related: Methods for Querying.

Also aliased as: value?
hash → an_integer
Source

    static VALUE
    rb_hash_hash(VALUE hash)
    {
        st_index_t size = RHASH_SIZE(hash);
        st_index_t hval = rb_hash_start(size);
        hval = rb_hash_uint(hval, (st_index_t)rb_hash_hash);
        if (size) {
            rb_hash_foreach(hash, hash_i, (VALUE)&hval);
        }
        hval = rb_hash_end(hval);
        return ST2FIX(hval);
    }

Returns the integer hash-code for the hash.

Two hashes have the same hash-code if their content is the same (regardless of order):

    h1 = {foo: 0, bar: 1, baz: 2}
    h2 = {baz: 2, bar: 1, foo: 0}
    h2.hash == h1.hash # => true
    h2.eql? h1 # => true

Related: see Methods for Querying.

include?(key) → true or false
Source

    VALUE
    rb_hash_has_key(VALUE hash, VALUE key)
    {
        return RBOOL(hash_stlike_lookup(hash, key, NULL));
    }

Returns whether `key` is a key in `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.include?(:bar) # => true
    h.include?(:BAR) # => false

Related: Methods for Querying.

Also aliased as: member?, has_key?, key?
initialize_copy
Source

    static VALUE
    rb_hash_replace(VALUE hash, VALUE hash2)
    {
        rb_hash_modify_check(hash);
        if (hash == hash2) return hash;
        if (hash_iterating_p(hash)) {
            rb_raise(rb_eRuntimeError, "can't replace hash during iteration");
        }
        hash2 = to_hash(hash2);

        COPY_DEFAULT(hash, hash2);

        if (RHASH_AR_TABLE_P(hash)) {
            hash_ar_free_and_clear_table(hash);
        }
        else {
            hash_st_free_and_clear_table(hash);
        }

        hash_copy(hash, hash2);

        return hash;
    }

Also aliased as: replace
inspect → new_string
Source

    static VALUE
    rb_hash_inspect(VALUE hash)
    {
        if (RHASH_EMPTY_P(hash))
            return rb_usascii_str_new2("{}");
        return rb_exec_recursive(inspect_hash, hash, 0);
    }

Returns a new string containing the hash entries:

    h = {foo: 0, bar: 1, baz: 2}
    h.inspect # => "{foo: 0, bar: 1, baz: 2}"

Related: see Methods for Converting.

Also aliased as: to_s
invert → new_hash
Source

    static VALUE
    rb_hash_invert(VALUE hash)
    {
        VALUE h = rb_hash_new_with_size(RHASH_SIZE(hash));

        rb_hash_foreach(hash, rb_hash_invert_i, h);
        return h;
    }

Returns a new hash with each key-value pair inverted:

    h = {foo: 0, bar: 1, baz: 2}
    h1 = h.invert
    h1 # => {0=>:foo, 1=>:bar, 2=>:baz}

Overwrites any repeated new keys (see Entry Order):

    h = {foo: 0, bar: 0, baz: 0}
    h.invert # => {0=>:baz}

Related: see Methods for Transforming Keys and Values.

keep_if {|key, value| ... } → self
keep_if → new_enumerator
Source

    static VALUE
    rb_hash_keep_if(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_modify_check(hash);
        if (!RHASH_TABLE_EMPTY_P(hash)) {
            rb_hash_foreach(hash, keep_if_i, hash);
        }
        return hash;
    }

With a block given, calls the block for each key-value pair; retains the entry if the block returns a truthy value; otherwise deletes the entry; returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.keep_if { |key, value| key.start_with?('b') } # => {bar: 1, baz: 2}

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

key(value) → key or nil
Source

    static VALUE
    rb_hash_key(VALUE hash, VALUE value)
    {
        VALUE args[2];

        args[0] = value;
        args[1] = Qnil;

        rb_hash_foreach(hash, key_i, (VALUE)args);

        return args[1];
    }

Returns the key for the first-found entry with the given `value` (see Entry Order):

    h = {foo: 0, bar: 2, baz: 2}
    h.key(0) # => :foo
    h.key(2) # => :bar

Returns `nil` if no such value is found.

Related: see Methods for Fetching.

key?
Alias for: include?
keys → new_array
Source

    VALUE
    rb_hash_keys(VALUE hash)
    {
        st_index_t size = RHASH_SIZE(hash);
        VALUE keys =  rb_ary_new_capa(size);

        if (size == 0) return keys;

        if (ST_DATA_COMPATIBLE_P(VALUE)) {
            RARRAY_PTR_USE(keys, ptr, {
                if (RHASH_AR_TABLE_P(hash)) {
                    size = ar_keys(hash, ptr, size);
                }
                else {
                    st_table *table = RHASH_ST_TABLE(hash);
                    size = st_keys(table, ptr, size);
                }
            });
            rb_gc_writebarrier_remember(keys);
            rb_ary_set_len(keys, size);
        }
        else {
            rb_hash_foreach(hash, keys_i, keys);
        }

        return keys;
    }

Returns a new array containing all keys in `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.keys # => [:foo, :bar, :baz]

Related: see Methods for Fetching.

length
Alias for: size
member?
Alias for: include?
merge(*other_hashes) → new_hash
merge(*other_hashes) { |key, old_value, new_value| ... } → new_hash
Source

    static VALUE
    rb_hash_merge(int argc, VALUE *argv, VALUE self)
    {
        return rb_hash_update(argc, argv, copy_compare_by_id(rb_hash_dup(self), self));
    }

Each argument `other_hash` in `other_hashes` must be a hash.

With arguments `other_hashes` given and no block, returns the new hash formed by merging each successive `other_hash` into a copy of `self`; returns that copy; for each successive entry in `other_hash`:

- For a new key, the entry is added at the end of `self`.

- For duplicate key, the entry overwrites the entry in `self`, whose position is unchanged.

Example:

    h = {foo: 0, bar: 1, baz: 2}
    h1 = {bat: 3, bar: 4}
    h2 = {bam: 5, bat:6}
    h.merge(h1, h2) # => {foo: 0, bar: 4, baz: 2, bat: 6, bam: 5}

With arguments `other_hashes` and a block given, behaves as above except that for a duplicate key the overwriting entry takes it value not from the entry in `other_hash`, but instead from the block:

- The block is called with the duplicate key and the values from both `self` and `other_hash`.

- The block’s return value becomes the new value for the entry in `self`.

Example:

    h = {foo: 0, bar: 1, baz: 2}
    h1 = {bat: 3, bar: 4}
    h2 = {bam: 5, bat:6}
    h.merge(h1, h2) { |key, old_value, new_value| old_value + new_value }
    # => {foo: 0, bar: 5, baz: 2, bat: 9, bam: 5}

With no arguments, returns a copy of `self`; the block, if given, is ignored.

Related: see Methods for Assigning.

merge!
Alias for: update
rassoc(value) → new_array or nil
Source

    static VALUE
    rb_hash_rassoc(VALUE hash, VALUE obj)
    {
        VALUE args[2];

        args[0] = obj;
        args[1] = Qnil;
        rb_hash_foreach(hash, rassoc_i, (VALUE)args);
        return args[1];
    }

Searches `self` for the first entry whose value is `==` to the given `value`; see Entry Order.

If the entry is found, returns its key and value as a 2-element array; returns `nil` if not found:

    h = {foo: 0, bar: 1, baz: 1}
    h.rassoc(1) # => [:bar, 1]

Related: see Methods for Fetching.

rehash → self
Source

    VALUE
    rb_hash_rehash(VALUE hash)
    {
        VALUE tmp;
        st_table *tbl;

        if (hash_iterating_p(hash)) {
            rb_raise(rb_eRuntimeError, "rehash during iteration");
        }
        rb_hash_modify_check(hash);
        if (RHASH_AR_TABLE_P(hash)) {
            tmp = hash_alloc(0);
            rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);

            hash_ar_free_and_clear_table(hash);
            ar_copy(hash, tmp);
        }
        else if (RHASH_ST_TABLE_P(hash)) {
            st_table *old_tab = RHASH_ST_TABLE(hash);
            tmp = hash_alloc(0);

            hash_st_table_init(tmp, old_tab->type, old_tab->num_entries);
            tbl = RHASH_ST_TABLE(tmp);

            rb_hash_foreach(hash, rb_hash_rehash_i, (VALUE)tmp);

            hash_st_free(hash);
            RHASH_ST_TABLE_SET(hash, tbl);
            RHASH_ST_CLEAR(tmp);
        }
        hash_verify(hash);
        return hash;
    }

Rebuilds the hash table for `self` by recomputing the hash index for each key; returns `self`. Calling this method ensures that the hash table is valid.

The hash table becomes invalid if the hash value of a key has changed after the entry was created. See Modifying an Active Hash Key.

reject {|key, value| ... } → new_hash
reject → new_enumerator
Source

    static VALUE
    rb_hash_reject(VALUE hash)
    {
        VALUE result;

        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        result = hash_dup_with_compare_by_id(hash);
        if (!RHASH_EMPTY_P(hash)) {
            rb_hash_foreach(result, delete_if_i, result);
            compact_after_delete(result);
        }
        return result;
    }

With a block given, returns a copy of `self` with zero or more entries removed; calls the block with each key-value pair; excludes the entry in the copy if the block returns a truthy value, includes it otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h.reject {|key, value| key.start_with?('b') }
    # => {foo: 0}

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

reject! {|key, value| ... } → self or nil
reject! → new_enumerator
Source

    static VALUE
    rb_hash_reject_bang(VALUE hash)
    {
        st_index_t n;

        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_modify(hash);
        n = RHASH_SIZE(hash);
        if (!n) return Qnil;
        rb_hash_foreach(hash, delete_if_i, hash);
        if (n == RHASH_SIZE(hash)) return Qnil;
        return hash;
    }

With a block given, calls the block with each entry’s key and value; removes the entry from `self` if the block returns a truthy value.

Return `self` if any entries were removed, `nil` otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h.reject! {|key, value| value < 2 } # => {baz: 2}
    h.reject! {|key, value| value < 2 } # => nil

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

replace(other_hash) → self

Replaces the entire contents of `self` with the contents of `other_hash`; returns `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.replace({bat: 3, bam: 4}) # => {bat: 3, bam: 4}

Also replaces the default value or proc of `self` with the default value or proc of `other_hash`.

    h = {}
    other = Hash.new(:ok)
    h.replace(other)
    h.default # => :ok

Related: see Methods for Assigning.

Alias for: initialize_copy
select {|key, value| ... } → new_hash
select → new_enumerator
Source

    static VALUE
    rb_hash_select(VALUE hash)
    {
        VALUE result;

        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        result = hash_dup_with_compare_by_id(hash);
        if (!RHASH_EMPTY_P(hash)) {
            rb_hash_foreach(result, keep_if_i, result);
            compact_after_delete(result);
        }
        return result;
    }

With a block given, calls the block with each entry’s key and value; returns a new hash whose entries are those for which the block returns a truthy value:

    h = {foo: 0, bar: 1, baz: 2}
    h.select {|key, value| value < 2 } # => {foo: 0, bar: 1}

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

Also aliased as: filter
select! {|key, value| ... } → self or nil
select! → new_enumerator
Source

    static VALUE
    rb_hash_select_bang(VALUE hash)
    {
        st_index_t n;

        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_modify_check(hash);
        n = RHASH_SIZE(hash);
        if (!n) return Qnil;
        rb_hash_foreach(hash, keep_if_i, hash);
        if (n == RHASH_SIZE(hash)) return Qnil;
        return hash;
    }

With a block given, calls the block with each entry’s key and value; removes from `self` each entry for which the block returns `false` or `nil`.

Returns `self` if any entries were removed, `nil` otherwise:

    h = {foo: 0, bar: 1, baz: 2}
    h.select! {|key, value| value < 2 } # => {foo: 0, bar: 1}
    h.select! {|key, value| value < 2 } # => nil

With no block given, returns a new `Enumerator`.

Related: see Methods for Deleting.

Also aliased as: filter!
shift → [key, value] or nil
Source

    static VALUE
    rb_hash_shift(VALUE hash)
    {
        struct shift_var var;

        rb_hash_modify_check(hash);
        if (RHASH_AR_TABLE_P(hash)) {
            var.key = Qundef;
            if (!hash_iterating_p(hash)) {
                if (ar_shift(hash, &var.key, &var.val)) {
                    return rb_assoc_new(var.key, var.val);
                }
            }
            else {
                rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
                if (!UNDEF_P(var.key)) {
                    rb_hash_delete_entry(hash, var.key);
                    return rb_assoc_new(var.key, var.val);
                }
            }
        }
        if (RHASH_ST_TABLE_P(hash)) {
            var.key = Qundef;
            if (!hash_iterating_p(hash)) {
                if (st_shift(RHASH_ST_TABLE(hash), &var.key, &var.val)) {
                    return rb_assoc_new(var.key, var.val);
                }
            }
            else {
                rb_hash_foreach(hash, shift_i_safe, (VALUE)&var);
                if (!UNDEF_P(var.key)) {
                    rb_hash_delete_entry(hash, var.key);
                    return rb_assoc_new(var.key, var.val);
                }
            }
        }
        return Qnil;
    }

Removes and returns the first entry of `self` as a 2-element array; see Entry Order:

    h = {foo: 0, bar: 1, baz: 2}
    h.shift # => [:foo, 0]
    h       # => {bar: 1, baz: 2}

Returns `nil` if `self` is empty.

Related: see Methods for Deleting.

size → integer
Source

    VALUE
    rb_hash_size(VALUE hash)
    {
        return INT2FIX(RHASH_SIZE(hash));
    }

Returns the count of entries in `self`:

    {foo: 0, bar: 1, baz: 2}.size # => 3

Related: see Methods for Querying.

Also aliased as: length
slice(*keys) → new_hash
Source

    static VALUE
    rb_hash_slice(int argc, VALUE *argv, VALUE hash)
    {
        int i;
        VALUE key, value, result;

        if (argc == 0 || RHASH_EMPTY_P(hash)) {
            return copy_compare_by_id(rb_hash_new(), hash);
        }
        result = copy_compare_by_id(rb_hash_new_with_size(argc), hash);

        for (i = 0; i < argc; i++) {
            key = argv[i];
            value = rb_hash_lookup2(hash, key, Qundef);
            if (!UNDEF_P(value))
                rb_hash_aset(result, key, value);
        }

        return result;
    }

Returns a new hash containing the entries from `self` for the given `keys`; ignores any keys that are not found:

    h = {foo: 0, bar: 1, baz: 2}
    h.slice(:baz, :foo, :nosuch) # => {baz: 2, foo: 0}

Related: see Methods for Deleting.

store
Alias for: []=
to_a → new_array
Source

    static VALUE
    rb_hash_to_a(VALUE hash)
    {
        VALUE ary;

        ary = rb_ary_new_capa(RHASH_SIZE(hash));
        rb_hash_foreach(hash, to_a_i, ary);

        return ary;
    }

Returns all elements of `self` as an array of 2-element arrays; each nested array contains a key-value pair from `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.to_a # => [[:foo, 0], [:bar, 1], [:baz, 2]]

Related: see Methods for Converting.

to_h {|key, value| ... } → new_hash
to_h → self or new_hash
Source

    static VALUE
    rb_hash_to_h(VALUE hash)
    {
        if (rb_block_given_p()) {
            return rb_hash_to_h_block(hash);
        }
        if (rb_obj_class(hash) != rb_cHash) {
            const VALUE flags = RBASIC(hash)->flags;
            hash = hash_dup(hash, rb_cHash, flags & RHASH_PROC_DEFAULT);
        }
        return hash;
    }

With a block given, returns a new hash whose content is based on the block; the block is called with each entry’s key and value; the block should return a 2-element array containing the key and value to be included in the returned array:

    h = {foo: 0, bar: 1, baz: 2}
    h.to_h {|key, value| [value, key] }
    # => {0 => :foo, 1 => :bar, 2 => :baz}

With no block given, returns `self` if `self` is an instance of `Hash`; if `self` is a subclass of `Hash`, returns a new hash containing the content of `self`.

Related: see Methods for Converting.

to_hash → self
Source

    static VALUE
    rb_hash_to_hash(VALUE hash)
    {
        return hash;
    }

Returns `self`.

Related: see Methods for Converting.

to_proc → proc
Source

    static VALUE
    rb_hash_to_proc(VALUE hash)
    {
        return rb_func_lambda_new(hash_proc_call, hash, 1, 1);
    }

Returns a `Proc` object that maps a key to its value:

    h = {foo: 0, bar: 1, baz: 2}
    proc = h.to_proc
    proc.class # => Proc
    proc.call(:foo) # => 0
    proc.call(:bar) # => 1
    proc.call(:nosuch) # => nil

Related: see Methods for Converting.

to_s
Alias for: inspect
transform_keys {|old_key| ... } → new_hash
transform_keys(other_hash) → new_hash
transform_keys(other_hash) {|old_key| ...} → new_hash
transform_keys → new_enumerator
Source

    static VALUE
    rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
    {
        VALUE result;
        struct transform_keys_args transarg = {0};

        argc = rb_check_arity(argc, 0, 1);
        if (argc > 0) {
            transarg.trans = to_hash(argv[0]);
            transarg.block_given = rb_block_given_p();
        }
        else {
            RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        }
        result = rb_hash_new();
        if (!RHASH_EMPTY_P(hash)) {
            if (transarg.trans) {
                transarg.result = result;
                rb_hash_foreach(hash, transform_keys_hash_i, (VALUE)&transarg);
            }
            else {
                rb_hash_foreach(hash, transform_keys_i, result);
            }
        }

        return result;
    }

With an argument, a block, or both given, derives a new hash `new_hash` from `self`, the argument, and/or the block; all, some, or none of its keys may be different from those in `self`.

With a block given and no argument, `new_hash` has keys determined only by the block.

For each key/value pair `old_key/value` in `self`, calls the block with `old_key`; the block’s return value becomes `new_key`; sets `new_hash[new_key] = value`; a duplicate key overwrites:

    h = {foo: 0, bar: 1, baz: 2}
    h.transform_keys {|old_key| old_key.to_s }
    # => {"foo" => 0, "bar" => 1, "baz" => 2}
    h.transform_keys {|old_key| 'xxx' }
    # => {"xxx" => 2}

With argument `other_hash` given and no block, `new_hash` may have new keys provided by `other_hash` and unchanged keys provided by `self`.

For each key/value pair `old_key/old_value` in `self`, looks for key `old_key` in `other_hash`:

- If `old_key` is found, its value `other_hash[old_key]` is taken as `new_key`; sets `new_hash[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys(baz: :BAZ, bar: :BAR, foo: :FOO)
      # => {FOO: 0, BAR: 1, BAZ: 2}
      h.transform_keys(baz: :FOO, bar: :FOO, foo: :FOO)
      # => {FOO: 2}

- If `old_key` is not found, sets `new_hash[old_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys({})
      # => {foo: 0, bar: 1, baz: 2}
      h.transform_keys(baz: :foo)
      # => {foo: 2, bar: 1}

Unused keys in `other_hash` are ignored:

    h = {foo: 0, bar: 1, baz: 2}
    h.transform_keys(bat: 3)
    # => {foo: 0, bar: 1, baz: 2}

With both argument `other_hash` and a block given, `new_hash` has new keys specified by `other_hash` or by the block, and unchanged keys provided by `self`.

For each pair `old_key` and `value` in `self`:

- If `other_hash` has key `old_key` (with value `new_key`), does not call the block for that key; sets `new_hash[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys(baz: :BAZ, bar: :BAR, foo: :FOO) {|key| fail 'Not called' }
      # => {FOO: 0, BAR: 1, BAZ: 2}

- If `other_hash` does not have key `old_key`, calls the block with `old_key` and takes its return value as `new_key`; sets `new_hash[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys(baz: :BAZ) {|key| key.to_s.reverse }
      # => {"oof" => 0, "rab" => 1, BAZ: 2}
      h.transform_keys(baz: :BAZ) {|key| 'ook' }
      # => {"ook" => 1, BAZ: 2}

With no argument and no block given, returns a new `Enumerator`.

Related: see Methods for Transforming Keys and Values.

transform_keys! {|old_key| ... } → self
transform_keys!(other_hash) → self
transform_keys!(other_hash) {|old_key| ...} → self
transform_keys! → new_enumerator
Source

    static VALUE
    rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
    {
        VALUE trans = 0;
        int block_given = 0;

        argc = rb_check_arity(argc, 0, 1);
        if (argc > 0) {
            trans = to_hash(argv[0]);
            block_given = rb_block_given_p();
        }
        else {
            RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        }
        rb_hash_modify_check(hash);
        if (!RHASH_TABLE_EMPTY_P(hash)) {
            long i;
            VALUE new_keys = hash_alloc(0);
            VALUE pairs = rb_ary_hidden_new(RHASH_SIZE(hash) * 2);
            rb_hash_foreach(hash, flatten_i, pairs);
            for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
                VALUE key = RARRAY_AREF(pairs, i), new_key, val;

                if (!trans) {
                    new_key = rb_yield(key);
                }
                else if (!UNDEF_P(new_key = rb_hash_lookup2(trans, key, Qundef))) {
                    /* use the transformed key */
                }
                else if (block_given) {
                    new_key = rb_yield(key);
                }
                else {
                    new_key = key;
                }
                val = RARRAY_AREF(pairs, i+1);
                if (!hash_stlike_lookup(new_keys, key, NULL)) {
                    rb_hash_stlike_delete(hash, &key, NULL);
                }
                rb_hash_aset(hash, new_key, val);
                rb_hash_aset(new_keys, new_key, Qnil);
            }
            rb_ary_clear(pairs);
            rb_hash_clear(new_keys);
        }
        compact_after_delete(hash);
        return hash;
    }

With an argument, a block, or both given, derives keys from the argument, the block, and `self`; all, some, or none of the keys in `self` may be changed.

With a block given and no argument, derives keys only from the block; all, some, or none of the keys in `self` may be changed.

For each key/value pair `old_key/value` in `self`, calls the block with `old_key`; the block’s return value becomes `new_key`; removes the entry for `old_key`: `self.delete(old_key)`; sets `self[new_key] = value`; a duplicate key overwrites:

    h = {foo: 0, bar: 1, baz: 2}
    h.transform_keys! {|old_key| old_key.to_s }
    # => {"foo" => 0, "bar" => 1, "baz" => 2}
    h = {foo: 0, bar: 1, baz: 2}
    h.transform_keys! {|old_key| 'xxx' }
    # => {"xxx" => 2}

With argument `other_hash` given and no block, derives keys for `self` from `other_hash` and `self`; all, some, or none of the keys in `self` may be changed.

For each key/value pair `old_key/old_value` in `self`, looks for key `old_key` in `other_hash`:

- If `old_key` is found, takes value `other_hash[old_key]` as `new_key`; removes the entry for `old_key`: `self.delete(old_key)`; sets `self[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :BAZ, bar: :BAR, foo: :FOO)
      # => {FOO: 0, BAR: 1, BAZ: 2}
      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :FOO, bar: :FOO, foo: :FOO)
      # => {FOO: 2}

- If `old_key` is not found, does nothing:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!({})
      # => {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :foo)
      # => {foo: 2, bar: 1}

Unused keys in `other_hash` are ignored:

    h = {foo: 0, bar: 1, baz: 2}
    h.transform_keys!(bat: 3)
    # => {foo: 0, bar: 1, baz: 2}

With both argument `other_hash` and a block given, derives keys from `other_hash`, the block, and `self`; all, some, or none of the keys in `self` may be changed.

For each pair `old_key` and `value` in `self`:

- If `other_hash` has key `old_key` (with value `new_key`), does not call the block for that key; removes the entry for `old_key`: `self.delete(old_key)`; sets `self[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :BAZ, bar: :BAR, foo: :FOO) {|key| fail 'Not called' }
      # => {FOO: 0, BAR: 1, BAZ: 2}

- If `other_hash` does not have key `old_key`, calls the block with `old_key` and takes its return value as `new_key`; removes the entry for `old_key`: `self.delete(old_key)`; sets `self[new_key] = value`; a duplicate key overwrites:

      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :BAZ) {|key| key.to_s.reverse }
      # => {"oof" => 0, "rab" => 1, BAZ: 2}
      h = {foo: 0, bar: 1, baz: 2}
      h.transform_keys!(baz: :BAZ) {|key| 'ook' }
      # => {"ook" => 1, BAZ: 2}

With no argument and no block given, returns a new `Enumerator`.

Related: see Methods for Transforming Keys and Values.

transform_values {|value| ... } → new_hash
transform_values → new_enumerator
Source

    static VALUE
    rb_hash_transform_values(VALUE hash)
    {
        VALUE result;

        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        result = hash_dup_with_compare_by_id(hash);
        SET_DEFAULT(result, Qnil);

        if (!RHASH_EMPTY_P(hash)) {
            transform_values(result);
            compact_after_delete(result);
        }

        return result;
    }

With a block given, returns a new hash `new_hash`; for each pair `key`/`value` in `self`, calls the block with `value` and captures its return as `new_value`; adds to `new_hash` the entry `key`/`new_value`:

    h = {foo: 0, bar: 1, baz: 2}
    h1 = h.transform_values {|value| value * 100}
    h1 # => {foo: 0, bar: 100, baz: 200}

With no block given, returns a new `Enumerator`.

Related: see Methods for Transforming Keys and Values.

transform_values! {|old_value| ... } → self
transform_values! → new_enumerator
Source

    static VALUE
    rb_hash_transform_values_bang(VALUE hash)
    {
        RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
        rb_hash_modify_check(hash);

        if (!RHASH_TABLE_EMPTY_P(hash)) {
            transform_values(hash);
        }

        return hash;
    }

With a block given, changes the values of `self` as determined by the block; returns `self`.

For each entry `key`/`old_value` in `self`, calls the block with `old_value`, captures its return value as `new_value`, and sets `self[key] = new_value`:

    h = {foo: 0, bar: 1, baz: 2}
    h.transform_values! {|value| value * 100} # => {foo: 0, bar: 100, baz: 200}

With no block given, returns a new `Enumerator`.

Related: see Methods for Transforming Keys and Values.

update(*other_hashes) → self
update(*other_hashes) { |key, old_value, new_value| ... } → self
Source

    static VALUE
    rb_hash_update(int argc, VALUE *argv, VALUE self)
    {
        struct update_call_args args = {
            .hash = self,
            .argv = argv,
            .argc = argc,
            .block_given = rb_block_given_p(),
            .iterating = false,
        };
        VALUE arg = (VALUE)&args;

        rb_hash_modify(self);
        return rb_ensure(rb_hash_update_call, arg, rb_hash_update_ensure, arg);
    }

Updates values and/or adds entries to `self`; returns `self`.

Each argument `other_hash` in `other_hashes` must be a hash.

With no block given, for each successive entry `key`/`new_value` in each successive `other_hash`:

- If `key` is in `self`, sets `self[key] = new_value`, whose position is unchanged:

      h0 = {foo: 0, bar: 1, baz: 2}
      h1 = {bar: 3, foo: -1}
      h0.update(h1) # => {foo: -1, bar: 3, baz: 2}

- If `key` is not in `self`, adds the entry at the end of `self`:

      h = {foo: 0, bar: 1, baz: 2}
      h.update({bam: 3, bah: 4}) # => {foo: 0, bar: 1, baz: 2, bam: 3, bah: 4}

With a block given, for each successive entry `key`/`new_value` in each successive `other_hash`:

- If `key` is in `self`, fetches `old_value` from `self[key]`, calls the block with `key`, `old_value`, and `new_value`, and sets `self[key] = new_value`, whose position is unchanged :

      season = {AB: 75, H: 20, HR: 3, SO: 17, W: 11, HBP: 3}
      today = {AB: 3, H: 1, W: 1}
      yesterday = {AB: 4, H: 2, HR: 1}
      season.update(yesterday, today) {|key, old_value, new_value| old_value + new_value }
      # => {AB: 82, H: 23, HR: 4, SO: 17, W: 12, HBP: 3}

- If `key` is not in `self`, adds the entry at the end of `self`:

      h = {foo: 0, bar: 1, baz: 2}
      h.update({bat: 3}) { fail 'Cannot happen' }
      # => {foo: 0, bar: 1, baz: 2, bat: 3}

Related: see Methods for Assigning.

Also aliased as: merge!
value?
Alias for: has_value?
values → new_array
Source

    VALUE
    rb_hash_values(VALUE hash)
    {
        VALUE values;
        st_index_t size = RHASH_SIZE(hash);

        values = rb_ary_new_capa(size);
        if (size == 0) return values;

        if (ST_DATA_COMPATIBLE_P(VALUE)) {
            if (RHASH_AR_TABLE_P(hash)) {
                rb_gc_writebarrier_remember(values);
                RARRAY_PTR_USE(values, ptr, {
                    size = ar_values(hash, ptr, size);
                });
            }
            else if (RHASH_ST_TABLE_P(hash)) {
                st_table *table = RHASH_ST_TABLE(hash);
                rb_gc_writebarrier_remember(values);
                RARRAY_PTR_USE(values, ptr, {
                    size = st_values(table, ptr, size);
                });
            }
            rb_ary_set_len(values, size);
        }
        else {
            rb_hash_foreach(hash, values_i, values);
        }

        return values;
    }

Returns a new array containing all values in `self`:

    h = {foo: 0, bar: 1, baz: 2}
    h.values # => [0, 1, 2]

Related: see Methods for Fetching.

values_at(*keys) → new_array
Source

    static VALUE
    rb_hash_values_at(int argc, VALUE *argv, VALUE hash)
    {
        VALUE result = rb_ary_new2(argc);
        long i;

        for (i=0; i<argc; i++) {
            rb_ary_push(result, rb_hash_aref(hash, argv[i]));
        }
        return result;
    }

Returns a new array containing values for the given `keys`:

    h = {foo: 0, bar: 1, baz: 2}
    h.values_at(:baz, :foo) # => [2, 0]

The hash default is returned for each key that is not found:

    h.values_at(:hello, :foo) # => [nil, 0]

Related: see Methods for Fetching.