From: "ko1 (Koichi Sasada)" <redmine@...>
Date: 2013-02-18T09:15:21+09:00
Subject: [ruby-core:52419] [ruby-trunk - Feature #7872] `block_given?` does not work inside `define_method`


Issue #7872 has been updated by ko1 (Koichi Sasada).

Assignee set to matz (Yukihiro Matsumoto)

(a) def...end and (b) define_method(...){...} is completely different.

(1) On (b), outer scope

  a = 1
  define_method(:foo) do
    p a # access to outer scope
  end

(2) (1) means that the passed block is outer block

  class C; end
  def def_method mid
    C.module_eval{
      define_method(mid) do
        p block_given?
        yield if block_given?
      end
    }
  end

  def_method(:foo)
  obj = C.new
  obj.foo
  obj.foo{p 1}
  
  def_method(:bar){p :def_foo}
  obj.bar
  obj.bar{p 2}

#=>

  false
  false
  true
  :def_foo
  true
  :def_foo

(3) You can pass block using block parameter

  define_method(:foo){|&b|
    p [b, block_given?]
  }
  foo   #=> [nil, false]
  foo{} #=> [#<Proc:0x22d08f0@t.rb:5>, false]


----------------------------------------
Feature #7872: `block_given?` does not work inside `define_method`
https://bugs.ruby-lang.org/issues/7872#change-36474

Author: alexeymuranov (Alexey Muranov)
Status: Open
Priority: Normal
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: next minor


=begin
Is this the expected behavior?

 define_method :try do
   block_given? ? yield : 'no block'
 end

 try { 'block' } # => "no block"

However:

 def try_again
   block_given? ? yield : 'no block'
 end

 try_again { 'block' } # => "block"

=end



-- 
http://bugs.ruby-lang.org/