Feature #12960: [psych] new visitor class to generate custom object instead of Hash

• Status: Third Party's Issue
• Assignee: -
• Target version: -

[kwatch (makoto kuwata)]

I create a patch to define new useful visitor class for Psych.
It generates custom object as mapping data instead of Hash.

Normally, you must access YAML document data like ydoc["foo"]["bar"]["baz"].
Using this class, you can access data like ydoc.foo.bar.baz.

Example1: create custom object instead of Hash according to context

    ## define custom classes
    Team   = Struct.new('Team', 'name', 'members')
    Member = Struct.new('Member', 'name', 'gender')
    ## create visitor object
    require 'psych'
    require 'psych/visitors/custom_class'
    classmap = {
      "teams"   => Team,
      "members" => Member,
    }
    visitor = Psych::Visitors::CustomClassVisitor.create(classmap)
    ## example YAML string
    input = <<-'END'
    teams:
      - name: SOS Brigade
        members:
          - {name: Haruhi, gender: F}
          - {name: Kyon,   gender: M}
          - {name: Mikuru, gender: F}
          - {name: Itsuki, gender: M}
          - {name: Yuki,   gender: F}
    END
    ## parse YAML string with creating Team or Member objects according to context
    tree = Psych.parse(input)
    ydoc = visitor.accept(tree)
    p ydoc['teams'][0].class                #=> Struct::Team
    p ydoc['teams'][0]['members'][0].class  #=> Struct::Member
    team = ydoc['teams'][0]
    p team.name                #=> "SOS Brigade"
    p team.members[0].name     #=> "Haruhi"
    p team.members[0].gender   #=> "F"

Example2: create custom hash object

    ## allows `hash.foo` instead of `hash["foo"]`
    class MagicHash < Hash
      def method_missing(method, *args)
        return super unless args.empty?
        return self[method.to_s]
      end
    end
    ## create visitor with MagicHash
    require 'psych'
    require 'psych/visitors/custom_class'
    classmap = {'*' => MagicHash}   # '*' means default class
    visitor = Psych::Visitors::CustomClassVisitor.create(classmap)
    ## example YAML document
    input = <<-'END'
    teams:
      - name: SOS Brigade
        members:
          - {name: Haruhi, gender: F}
          - {name: Kyon,   gender: M}
          - {name: Mikuru, gender: F}
          - {name: Itsuki, gender: M}
          - {name: Yuki,   gender: F}
    END
    ## parse YAML string with creating custom hash object instead of Hash
    tree = Psych.parse(input)
    ydoc = visitor.accept(tree)
    p ydoc.class                            #=> MagicHash
    p ydoc['teams'][0].class                #=> MagicHash
    p ydoc['teams'][0]['members'][0].class  #=> MagicHash
    p ydoc.teams[0].members[0].name    #=> "Haruhi"
    p ydoc.teams[0].members[0].gender  #=> "F"

I believe this class is very useful, and hope it to be imported into ruby repository.
Let me know your opinion or impression.

[kwatch (makoto kuwata)]

• File 0010-feat-psych-add-another-test-case.patch 0010-feat-psych-add-another-test-case.patch added

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Third Party's Issue

Please send to the upstream.

[kwatch (makoto kuwata)]

Nobuyoshi Nakada wrote:

Please send to the upstream.

I understand. Thx.

(I can't find any button to close this issue. Please close this.)

[duerst (Martin Dürst)]

makoto kuwata wrote:

(I can't find any button to close this issue. Please close this.)

The status is already "Third Party's Issue". You can think about this as a subcategory of "Closed".