Module: YAML

Module

YAML

In:

YAML

YAML(tm) (rhymes with ‘camel’) is a straightforward machine parsable data serialization format designed for human readability and interaction with scripting languages such as Perl and Python. YAML is optimized for data serialization, formatted dumping, configuration files, log files, Internet messaging and filtering. This specification describes the YAML information model and serialization format. Together with the Unicode standard for characters, it provides all the information necessary to understand YAML Version 1.0 and construct computer programs to process it.

See yaml.org/ for more information. For a quick tutorial, please visit YAML In Five Minutes (yaml.kwiki.org/?YamlInFiveMinutes).

About This Library

The YAML 1.0 specification outlines four stages of YAML loading and dumping. This library honors all four of those stages, although data is really only available to you in three stages.

The four stages are: native, representation, serialization, and presentation.

The native stage refers to data which has been loaded completely into Ruby’s own types. (See +YAML::load+.)

The representation stage means data which has been composed into +YAML::BaseNode+ objects. In this stage, the document is available as a tree of node objects. You can perform YPath queries and transformations at this level. (See +YAML::parse+.)

The serialization stage happens inside the parser. The YAML parser used in Ruby is called Syck. Serialized nodes are available in the extension as SyckNode structs.

The presentation stage is the YAML document itself. This is accessible to you as a string. (See +YAML::dump+.)

For more information about the various information models, see Chapter 3 of the YAML 1.0 Specification (yaml.org/spec/#id2491269).

The YAML module provides quick access to the most common loading (YAML::load) and dumping (YAML::dump) tasks. This module also provides an API for registering global types (YAML::add_domain_type).

Example

A simple round-trip (load and dump) of an object.

    require "yaml"

    test_obj = ["dogs", "cats", "badgers"]

    yaml_obj = YAML::dump( test_obj )
                        # -> ---
                             - dogs
                             - cats
                             - badgers
    ruby_obj = YAML::load( yaml_obj )
                        # => ["dogs", "cats", "badgers"]
    ruby_obj == test_obj
                        # => true

To register your custom types with the global resolver, use add_domain_type.

    YAML::add_domain_type( "your-site.com,2004", "widget" ) do |type, val|
        Widget.new( val )
    end

Constants

 YAML::Syck::Resolver
 YAML::Syck::DefaultResolver
 YAML::Syck::GenericResolver
 YAML::Syck::Parser
 YAML::Syck::Emitter

Public Class methods

add_builtin_type( type_tag, &transfer_proc )

Add a transfer method for a builtin type

     # File lib/yaml.rb, line 306
306:         def YAML.add_builtin_type( type_tag, &transfer_proc )
307:             resolver.add_type( "tag:yaml.org,2002:#{ type_tag }", transfer_proc )
308:         end

add_domain_type( domain, type_tag, &transfer_proc )

Add a global handler for a YAML domain type.

     # File lib/yaml.rb, line 299
299:         def YAML.add_domain_type( domain, type_tag, &transfer_proc )
300:         resolver.add_type( "tag:#{ domain }:#{ type_tag }", transfer_proc )
301:         end

add_private_type( type_re, &transfer_proc )

Add a private document type

     # File lib/yaml.rb, line 320
320:         def YAML.add_private_type( type_re, &transfer_proc )
321:             resolver.add_type( "x-private:" + type_re, transfer_proc )
322:         end

add_ruby_type( type, &transfer_proc )

Add a transfer method for a builtin type

     # File lib/yaml.rb, line 313
313:         def YAML.add_ruby_type( type, &transfer_proc )
314:             resolver.add_type( "tag:ruby.yaml.org,2002:#{ type_tag }", transfer_proc )
315:         end

detect_implicit( val )

Detect typing of a string

     # File lib/yaml.rb, line 327
327:     def YAML.detect_implicit( val )
328:         resolver.detect_implicit( val )
329:     end

dump( obj, io = nil )

Converts obj to YAML and writes the YAML result to io.

  File.open( 'animals.yaml', 'w' ) do |out|
    YAML.dump( ['badger', 'elephant', 'tiger'], out )
  end

If no io is provided, a string containing the dumped YAML is returned.

  YAML.dump( :locked )
     #=> "--- :locked"

     # File lib/yaml.rb, line 116
116:         def YAML.dump( obj, io = nil )
117:         obj.to_yaml( io || io2 = StringIO.new )
118:         io || ( io2.rewind; io2.read )
119:         end

dump_stream( *objs )

Returns a YAML stream containing each of the items in objs, each having their own document.

  YAML.dump_stream( 0, [], {} )
    #=> --- 0
        --- []
        --- {}

     # File lib/yaml.rb, line 288
288:         def YAML.dump_stream( *objs )
289:                 d = YAML::Stream.new
290:         objs.each do |doc|
291:                         d.add( doc ) 
292:         end
293:         d.emit
294:         end

each_document( io, &block )

Calls block with each consecutive document in the YAML stream contained in io.

  File.open( 'many-docs.yaml' ) do |yf|
    YAML.each_document( yf ) do |ydoc|
      ## ydoc contains the single object
      ## from the YAML document
    end
  end

     # File lib/yaml.rb, line 216
216:         def YAML.each_document( io, &block )
217:                 yp = parser.load_documents( io, &block )
218:     end

each_node( io, &doc_proc )

Calls block with a tree of +YAML::BaseNodes+, one tree for each consecutive document in the YAML stream contained in io.

  File.open( 'many-docs.yaml' ) do |yf|
    YAML.each_node( yf ) do |ydoc|
      ## ydoc contains a tree of nodes
      ## from the YAML document
    end
  end

     # File lib/yaml.rb, line 246
246:         def YAML.each_node( io, &doc_proc )
247:                 yp = generic_parser.load_documents( io, &doc_proc )
248:     end

Returns a new default emitter

     # File lib/yaml.rb, line 101
101:     def YAML.emitter; Emitter.new.set_resolver( YAML.resolver ); end

generic_parser()

Returns a new generic parser

    # File lib/yaml.rb, line 97
97:     def YAML.generic_parser; Parser.new.set_resolver( GenericResolver ); end

Load a document from the current io stream.

  File.open( 'animals.yaml' ) { |yf| YAML::load( yf ) }
     #=> ['badger', 'elephant', 'tiger']

Can also load from a string.

  YAML.load( "--- :locked" )
     #=> :locked

     # File lib/yaml.rb, line 132
132:         def YAML.load( io )
133:                 yp = parser.load( io )
134:         end

load_documents( io, &doc_proc )

Calls block with each consecutive document in the YAML stream contained in io.

  File.open( 'many-docs.yaml' ) do |yf|
    YAML.load_documents( yf ) do |ydoc|
      ## ydoc contains the single object
      ## from the YAML document
    end
  end

     # File lib/yaml.rb, line 231
231:         def YAML.load_documents( io, &doc_proc )
232:                 YAML.each_document( io, &doc_proc )
233:     end

load_file( filepath )

Load a document from the file located at filepath.

  YAML.load_file( 'animals.yaml' )
     #=> ['badger', 'elephant', 'tiger']

     # File lib/yaml.rb, line 142
142:     def YAML.load_file( filepath )
143:         File.open( filepath ) do |f|
144:             load( f )
145:         end
146:     end

load_stream( io )

Loads all documents from the current io stream, returning a +YAML::Stream+ object containing all loaded documents.

     # File lib/yaml.rb, line 270
270:         def YAML.load_stream( io )
271:                 d = nil
272:                 parser.load_documents( io ) do |doc|
273:                         d = YAML::Stream.new if not d
274:                         d.add( doc ) 
275:         end
276:                 return d
277:         end

object_maker( obj_class, val )

Allocate blank object

     # File lib/yaml.rb, line 365
365:     def YAML.object_maker( obj_class, val )
366:         if Hash === val
367:             o = obj_class.allocate
368:             val.each_pair { |k,v|
369:                 o.instance_variable_set("@#{k}", v)
370:             }
371:             o
372:         else
373:             raise YAML::Error, "Invalid object explicitly tagged !ruby/Object: " + val.inspect
374:         end
375:     end

Parse the first document from the current io stream

  File.open( 'animals.yaml' ) { |yf| YAML::load( yf ) }
     #=> #<YAML::Syck::Node:0x82ccce0
          @kind=:seq,
          @value=
           [#<YAML::Syck::Node:0x82ccd94
             @kind=:scalar,
             @type_id="str",
             @value="badger">,
            #<YAML::Syck::Node:0x82ccd58
             @kind=:scalar,
             @type_id="str",
             @value="elephant">,
            #<YAML::Syck::Node:0x82ccd1c
             @kind=:scalar,
             @type_id="str",
             @value="tiger">]>

Can also load from a string.

  YAML.parse( "--- :locked" )
     #=> #<YAML::Syck::Node:0x82edddc
           @type_id="tag:ruby.yaml.org,2002:sym",
           @value=":locked", @kind=:scalar>

     # File lib/yaml.rb, line 175
175:         def YAML.parse( io )
176:                 yp = generic_parser.load( io )
177:         end

parse_documents( io, &doc_proc )

Calls block with a tree of +YAML::BaseNodes+, one tree for each consecutive document in the YAML stream contained in io.

  File.open( 'many-docs.yaml' ) do |yf|
    YAML.parse_documents( yf ) do |ydoc|
      ## ydoc contains a tree of nodes
      ## from the YAML document
    end
  end

     # File lib/yaml.rb, line 261
261:         def YAML.parse_documents( io, &doc_proc )
262:                 YAML.each_node( io, &doc_proc )
263:     end

parse_file( filepath )

Parse a document from the file located at filepath.

  YAML.parse_file( 'animals.yaml' )
     #=> #<YAML::Syck::Node:0x82ccce0
          @kind=:seq,
          @value=
           [#<YAML::Syck::Node:0x82ccd94
             @kind=:scalar,
             @type_id="str",
             @value="badger">,
            #<YAML::Syck::Node:0x82ccd58
             @kind=:scalar,
             @type_id="str",
             @value="elephant">,
            #<YAML::Syck::Node:0x82ccd1c
             @kind=:scalar,
             @type_id="str",
             @value="tiger">]>

     # File lib/yaml.rb, line 199
199:     def YAML.parse_file( filepath )
200:         File.open( filepath ) do |f|
201:             parse( f )
202:         end
203:     end

Returns a new default parser

    # File lib/yaml.rb, line 95
95:     def YAML.parser; Parser.new.set_resolver( YAML.resolver ); end

quick_emit( oid, opts = {}, &e )

Allocate an Emitter if needed

     # File lib/yaml.rb, line 380
380:         def YAML.quick_emit( oid, opts = {}, &e )
381:         out = 
382:             if opts.is_a? YAML::Emitter
383:                 opts
384:             else
385:                 emitter.reset( opts )
386:             end
387:         out.emit( oid, &e )
388:         end

read_type_class( type, obj_class )

Method to extract colon-seperated type and class, returning the type and the constant of the class

     # File lib/yaml.rb, line 356
356:     def YAML.read_type_class( type, obj_class )
357:         scheme, domain, type, tclass = type.split( ':', 4 )
358:         tclass.split( "::" ).each { |c| obj_class = obj_class.const_get( c ) } if tclass
359:         return [ type, obj_class ]
360:     end

Returns the default resolver

    # File lib/yaml.rb, line 99
99:     def YAML.resolver; DefaultResolver; end

tagurize( val )

Convert a type_id to a taguri

     # File lib/yaml.rb, line 334
334:     def YAML.tagurize( val )
335:         resolver.tagurize( val )
336:     end

transfer( type_id, obj )

Apply a transfer method to a Ruby object

     # File lib/yaml.rb, line 341
341:     def YAML.transfer( type_id, obj )
342:         resolver.transfer( YAML.tagurize( type_id ), obj )
343:     end

try_implicit( obj )

Apply any implicit a node may qualify for

     # File lib/yaml.rb, line 348
348:         def YAML.try_implicit( obj )
349:                 YAML.transfer( YAML.detect_implicit( obj ), obj )
350:         end