From: Robert Klemme <shortcutter@...>
Date: 2007-04-30T19:05:04+09:00
Subject: Re: Ways to change the behavior of a block

On 30.04.2007 07:31, Brian Guthrie wrote:
> I'd like to be able to change the behavior of a call to a block (I'm
> working on a design-by-contract system and would like to be able to
> check the block's signature, filtering each call through some contract
> check) and I was wondering if anyone had any advice.  It's easy enough
> to override Proc#call, but doing so doesn't appear to affect calls to
> implicit blocks with using the yield keyword.  Is it even possible to
> do this?

If I understand you properly you want to be checking the argument list 
in the *calling* method.

irb(main):003:0> def f(&b)
irb(main):004:1> raise ArgumentError unless b.arity == 4
irb(main):005:1> b[0,1,2,3]
irb(main):006:1> end
=> nil
irb(main):007:0> f {|a,b| p a,b}
ArgumentError: ArgumentError
         from (irb):4:in `f'
         from (irb):7
         from :0
irb(main):008:0> f {|a,b,c,d| p a,b}
0
1
=> nil

Kind regards

	robert