From: Brian Mitchell <binary42@...>
Date: 2005-09-21T00:03:03+09:00
Subject: Re: Block that takes a block

On 9/20/05, Edward Faulkner <ef@alum.mit.edu> wrote:
>
> How can I make a block that takes a block argument?  This doesn't parse:
>
> myproc = proc{|&blk| [1,2,3].each(&blk)}
>
> The main reason I want to do this is to create a method with
> 'define_method' that takes a block argument.
>
> For example, the 'before' method below works fine, until you apply it
> to a method that takes a block.
>
> class Object
>   # Is there a built-in way to do this?
>   def metaclass; class << self; self; end; end
>
>   # Call blk before each invocation of method_name
>   def before(method_name, &blk)
>     oldblk = method(method_name)
>     metaclass.instance_eval {
>       define_method(method_name){|*args|
>         blk.call(*args)
>         oldblk.call(*args)
>       }
>     }
>   end
> end
>
> thanks,
> Ed
>
>
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I believe this is a limitation in the current 1.8 series. This has
been lifted in HEAD.

You might want to consider using a smart intermediate method that is a
wrapper around the block which can safely take an instance of Proc.

Brian.