From: "David A. Black" <dblack@...>
Date: 2008-08-27T00:18:50+09:00
Subject: Re: Passing a block with define_method

Hi --

On Wed, 27 Aug 2008, David A. Black wrote:

> Hi --
>
> On Wed, 27 Aug 2008, James Coglan wrote:
>
>>> module_eval a string.
>> 
>> 
>> 
>> I'm actually wrapping existing methods so I need to use define_method to
>> retain access to the old method. Here's my (broken) code so far:
>> 
>> module Continuations
>>  def accepts_continuation(*args)
>>    args.each do |method_name|
>>      func = instance_method(method_name)
>>      define_method(method_name) do |*params, &block|
>>        value = func.bind(self).call(*params)
>>      end
>>    end
>>  end
>> end
>
> In Ruby 1.9 you can do this:
>
>>> func = ->(*a,&block) { block.call if block; puts a }
> => #<Proc:0x388bdc@(irb):1 (lambda)>
>>> C = Class.new { define_method(:hi, &func) }
> => C
>>> C.new.hi(10) { puts "In block" }
> In block
> 10
>
> The ->(){} thing lets you create a lambda with method-argument
> semantics.

Actually the fix is in: you can now (and I think permanently) do this
in 1.9 without the ->(){}.

>> class C; define_method(:hi) {|*a,&block| block.call if block; puts
>> a }; end
=> #<Proc:0x1d5754@(irb):1 (lambda)>
>> C.new.hi(10) { puts "In block" }
In block
10

I'd lost track of where this stood -- I'm very glad to see that it's
there in the block syntax (thanks to Eric Mahurin's patch, if I'm not
mistaken).


David

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