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Filename : tag.rb
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# -*- mode: ruby; ruby-indent-level: 4; tab-width: 4 -*- vim: sw=4 ts=4
# $Id: tag.rb 16084 2008-04-19 11:45:39Z knu $
#
# = yaml/tag.rb: methods for associating a taguri to a class.
#
# Author:: why the lucky stiff
# 
module YAML
    # A dictionary of taguris which map to
    # Ruby classes.
    @@tagged_classes = {}
    
    # 
    # Associates a taguri _tag_ with a Ruby class _cls_.  The taguri is used to give types
    # to classes when loading YAML.  Taguris are of the form:
    #
    #   tag:authorityName,date:specific
    #
    # The +authorityName+ is a domain name or email address.  The +date+ is the date the type
    # was issued in YYYY or YYYY-MM or YYYY-MM-DD format.  The +specific+ is a name for
    # the type being added.
    # 
    # For example, built-in YAML types have 'yaml.org' as the +authorityName+ and '2002' as the
    # +date+.  The +specific+ is simply the name of the type:
    #
    #  tag:yaml.org,2002:int
    #  tag:yaml.org,2002:float
    #  tag:yaml.org,2002:timestamp
    #
    # The domain must be owned by you on the +date+ declared.  If you don't own any domains on the
    # date you declare the type, you can simply use an e-mail address.
    #
    #  tag:why@ruby-lang.org,2004:notes/personal
    #
    def YAML.tag_class( tag, cls )
        if @@tagged_classes.has_key? tag
            warn "class #{ @@tagged_classes[tag] } held ownership of the #{ tag } tag"
        end
        @@tagged_classes[tag] = cls
    end

    # Returns the complete dictionary of taguris, paired with classes.  The key for
    # the dictionary is the full taguri.  The value for each key is the class constant
    # associated to that taguri.
    #
    #  YAML.tagged_classes["tag:yaml.org,2002:int"] => Integer
    #
    def YAML.tagged_classes
        @@tagged_classes
    end
end

class Module
    # :stopdoc:

    # Adds a taguri _tag_ to a class, used when dumping or loading the class
    # in YAML.  See YAML::tag_class for detailed information on typing and
    # taguris.
    def yaml_as( tag, sc = true )
        verbose, $VERBOSE = $VERBOSE, nil
        class_eval <<-"end;", __FILE__, __LINE__+1
            attr_writer :taguri
            def taguri
                if respond_to? :to_yaml_type
                    YAML::tagurize( to_yaml_type[1..-1] )
                else
                    return @taguri if defined?(@taguri) and @taguri
                    tag = #{ tag.dump }
                    if self.class.yaml_tag_subclasses? and self.class != YAML::tagged_classes[tag]
                        tag = "\#{ tag }:\#{ self.class.yaml_tag_class_name }"
                    end
                    tag
                end
            end
            def self.yaml_tag_subclasses?; #{ sc ? 'true' : 'false' }; end
        end;
        YAML::tag_class tag, self
    ensure
        $VERBOSE = verbose
    end
    # Transforms the subclass name into a name suitable for display
    # in a subclassed tag.
    def yaml_tag_class_name
        self.name
    end
    # Transforms the subclass name found in the tag into a Ruby
    # constant name.
    def yaml_tag_read_class( name )
        name
    end
end