class Psych::Handler - Documentation for Ruby 4.0
Description: class Psych::Handler: Parser. Handler and define events that they can handle.
Keywords: ruby,class,Psych::Handler

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# class Psych::Handler

`Psych::Handler` is an abstract base class that defines the events used when dealing with `Psych::Parser`. Clients who want to use `Psych::Parser` should implement a class that inherits from `Psych::Handler` and define events that they can handle.

`Psych::Handler` defines all events that `Psych::Parser` can possibly send to event handlers.

See `Psych::Parser` for more details

### Constants

EVENTS

  Events that a `Handler` should respond to.

OPTIONS

  Default dumping options

### Public Instance Methods

alias (anchor)
Source

    # File ext/psych/lib/psych/handler.rb, line 110
    def alias anchor
    end

Called when an alias is found to `anchor`. `anchor` will be the name of the anchor found.

### Example

Here we have an example of an array that references itself in YAML:

    --- &ponies
    - first element
    - *ponies

&ponies is the anchor, *ponies is the alias. In this case, alias is called with “ponies”.

empty ()
Source

    # File ext/psych/lib/psych/handler.rb, line 236
    def empty
    end

Called when an empty event happens. (Which, as far as I can tell, is never).

end_document (implicit)
Source

    # File ext/psych/lib/psych/handler.rb, line 93
    def end_document implicit
    end

Called with the document ends. `implicit` is a boolean value indicating whether or not the document has an implicit ending.

### Example

Given the following YAML:

    ---
      hello world

`implicit` will be true. Given this YAML:

    ---
      hello world
    ...

`implicit` will be false.

end_mapping ()
Source

    # File ext/psych/lib/psych/handler.rb, line 230
    def end_mapping
    end

Called when a map ends

end_sequence ()
Source

    # File ext/psych/lib/psych/handler.rb, line 191
    def end_sequence
    end

Called when a sequence ends.

end_stream ()
Source

    # File ext/psych/lib/psych/handler.rb, line 241
    def end_stream
    end

Called when the `YAML` stream ends

event_location (start_line, start_column, end_line, end_column)
Source

    # File ext/psych/lib/psych/handler.rb, line 246
    def event_location(start_line, start_column, end_line, end_column)
    end

Called before each event with line/column information.

scalar (value, anchor, tag, plain, quoted, style)
Source

    # File ext/psych/lib/psych/handler.rb, line 150
    def scalar value, anchor, tag, plain, quoted, style
    end

Called when a scalar `value` is found. The scalar may have an `anchor`, a `tag`, be implicitly `plain` or implicitly `quoted`

`value` is the string value of the scalar `anchor` is an associated anchor or nil `tag` is an associated tag or nil `plain` is a boolean value `quoted` is a boolean value `style` is an integer indicating the string style

See the constants in `Psych::Nodes::Scalar` for the possible values of `style`

### Example

Here is a `YAML` document that exercises most of the possible ways this method can be called:

    ---
    - !str "foo"
    - &anchor fun
    - many
      lines
    - |
      many
      newlines

The above `YAML` document contains a list with four strings. Here are the parameters sent to this method in the same order:

    # value               anchor    tag     plain   quoted  style
    ["foo",               nil,      "!str", false,  false,  3    ]
    ["fun",               "anchor", nil,    true,   false,  1    ]
    ["many lines",        nil,      nil,    true,   false,  1    ]
    ["many\nnewlines\n",  nil,      nil,    false,  true,   4    ]

start_document (version, tag_directives, implicit)
Source

    # File ext/psych/lib/psych/handler.rb, line 72
    def start_document version, tag_directives, implicit
    end

Called when the document starts with the declared `version`, `tag_directives`, if the document is `implicit`.

`version` will be an array of integers indicating the `YAML` version being dealt with, `tag_directives` is a list of tuples indicating the prefix and suffix of each tag, and `implicit` is a boolean indicating whether the document is started implicitly.

### Example

Given the following YAML:

    %YAML 1.1
    %TAG ! tag:tenderlovemaking.com,2009:
    --- !squee

The parameters for `start_document` must be this:

    version         # => [1, 1]
    tag_directives  # => [["!", "tag:tenderlovemaking.com,2009:"]]
    implicit        # => false

start_mapping (anchor, tag, implicit, style)
Source

    # File ext/psych/lib/psych/handler.rb, line 225
    def start_mapping anchor, tag, implicit, style
    end

Called when a map starts.

`anchor` is the anchor associated with the map or `nil`. `tag` is the tag associated with the map or `nil`. `implicit` is a boolean indicating whether or not the map was implicitly started. `style` is an integer indicating the mapping style.

See the constants in `Psych::Nodes::Mapping` for the possible values of `style`.

### Example

Here is a `YAML` document that exercises most of the possible ways this method can be called:

    ---
    k: !!map { hello: world }
    v: &pewpew
      hello: world

The above `YAML` document consists of three maps, an outer map that contains two inner maps. Below is a matrix of the parameters sent in order to represent these three maps:

    # anchor    tag                       implicit  style
    [nil,       nil,                      true,     1     ]
    [nil,       "tag:yaml.org,2002:map",  false,    2     ]
    ["pewpew",  nil,                      true,     1     ]

start_sequence (anchor, tag, implicit, style)
Source

    # File ext/psych/lib/psych/handler.rb, line 186
    def start_sequence anchor, tag, implicit, style
    end

Called when a sequence is started.

`anchor` is the anchor associated with the sequence or nil. `tag` is the tag associated with the sequence or nil. `implicit` a boolean indicating whether or not the sequence was implicitly started. `style` is an integer indicating the list style.

See the constants in `Psych::Nodes::Sequence` for the possible values of `style`.

### Example

Here is a `YAML` document that exercises most of the possible ways this method can be called:

    ---
    - !!seq [
      a
    ]
    - &pewpew
      - b

The above `YAML` document consists of three lists, an outer list that contains two inner lists. Here is a matrix of the parameters sent to represent these lists:

    # anchor    tag                       implicit  style
    [nil,       nil,                      true,     1     ]
    [nil,       "tag:yaml.org,2002:seq",  false,    2     ]
    ["pewpew",  nil,                      true,     1     ]

start_stream (encoding)
Source

    # File ext/psych/lib/psych/handler.rb, line 47
    def start_stream encoding
    end

Called with `encoding` when the `YAML` stream starts. This method is called once per stream. A stream may contain multiple documents.

See the constants in `Psych::Parser` for the possible values of `encoding`.

streaming? ()
Source

    # File ext/psych/lib/psych/handler.rb, line 251
    def streaming?
      false
    end

Is this handler a streaming handler?