Subclassed Hash with overridden #initialize cannot be deserialized

[mbklein]

#!/usr/bin/env ruby

gem 'psych', '2.0.5'
require 'psych'

class HashThing < Hash
  attr :obj
  def initialize(obj)
    @obj = obj
  end
end

a = [1,2,3,4,5]
t1 = HashThing.new(a)
t2 = Psych.load(Psych.dump(t1))
puts t2.obj

The YAML.load line raises ArgumentError: wrong number of arguments (0 for 1).

It only seems to be a problem with Hash descendants. Array and String both work as expected; I haven't bothered to test any other classes.

Tested with different combinations of the following:

• Ruby 1.9.3 (p429 and p545), 2.0.0 (p451), 2.1.0 (p0)
• Psych 1.2.2, 1.3.4, 2.0.5

Backtrace (from Ruby 2.1.0/Psych 2.0.5):

./psych_bug.rb:8:in `initialize': wrong number of arguments (0 for 1) (ArgumentError)
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/to_ruby.rb:263:in `new'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/to_ruby.rb:263:in `visit_Psych_Nodes_Mapping'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/visitor.rb:15:in `visit'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/visitor.rb:5:in `accept'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/to_ruby.rb:31:in `accept'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/to_ruby.rb:278:in `visit_Psych_Nodes_Document'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/visitor.rb:15:in `visit'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/visitor.rb:5:in `accept'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/visitors/to_ruby.rb:31:in `accept'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych/nodes/node.rb:37:in `to_ruby'
    from .../lib/ruby/gems/2.1.0/gems/psych-2.0.5/lib/psych.rb:246:in `load'
    from ./psych_bug.rb:15:in `<main>'

[jrafanie]

See #43. We have a workaround that's less than ideal but it works. I'm assuming that Hash.new runs through C code and doesn't invoke your initialize in ruby land, hence you get (0 for 1). I'd recommend against subclassing Hash but if you have to, you can set instance variables and use a workaround like ours.

[tenderlove]

Seems it was because I was calling new on the Hash class, rather than allocate.