From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-10-24T03:09:20+09:00
Subject: Re: Re-naming a block

On Sat, Oct 23, 2010 at 7:43 PM, Andrew Wagner <wagner.andrew@gmail.com> wrote:
> Hi all.
>
> I'm writing a method which takes a block and returns a lambda which will
> execute that block when called. Here's the code:
>
> def foo &block
>  Proc.new { yield }
> end
>
> a = foo { 3 }
> puts a
>
>
> This returns something like #<Proc:0x2a50b08@scratch2.rb:2 (lambda)>. That's
> all well and good, but what I'd really like is for that line number to show
> up as 5, since that's where the block is actually defined. So I try this:
>
> def foo &block
>  a = Proc.new { yield }
>  def a.to_s
>    block.to_s
>  end
>  a
> end
>
> a = foo { 3 }
> puts a
>
> But here, ruby tells me that 'block' is undefined inside a's to_s. It's
> clearly not creating the closure I'd hoped for. I've played around with a
> few variations, but can't seem to get it to do what I want. Suggestions?

def creates a new scope, not a closure. Try define_method:

def foo &block
  a = Proc.new {yield}
  class << a; self; end.send(:define_method, :to_s) {block.to_s}
  a
end

Jesus.