From: Kristof Bastiaensen <kristof@...>
Date: 2004-08-05T20:56:35+09:00
Subject: Re: Macros in Ruby

On Thu, 05 Aug 2004 12:15:20 +0200, Robert Klemme wrote:
>> The difference which I can think of are: - Argument passing, a block
>> isn't strict about the arguments
>>   it gets passed, (i.e. it can take any argument).  A Proc object in
>>   contrast is strict (like methods).  The reason I can think of is that
>>   it is often usefull not to get all arguments in a block, i.e. 3.times{
>>   puts "Hi, world!" }
> 
> I don't know what exactly you mean by this.  Argument passing is the same
> for blocks and procs IMHO.  Can you explain the difference?

Oh, it seems I was wrong (after looking it up with ri).
What I said in the previous post only applies to procs created
with lambda (including the return thing), not procs created with
Proc.new.
So I guess that Proc.new creates exactly the same Proc object
as a block does (in the case that a Proc object gets created
from a block).  Only lambda expressions are different.
That would also mean that the best way to get rid of the 
LocalJumpError problem is to use a lambda expression.

Here is an example about what I meant with argument passing:

b1 = Proc.new { |a,b| 
   puts "a == #{a.inspect}, b == #{b.inspect}" }
b2 = lambda { |a,b|
   puts "a == #{a.inspect}, b == #{b.inspect}" }

b1[1]
b2[1]
#--- output: ----
a == 1, b == nil
/tmp/blocks.rb:5: wrong number of arguments (1 for 2) (ArgumentError)
        from /tmp/blocks.rb:5:in `[]'
        from /tmp/blocks.rb:9
#----------------

Sorry for the confusion.

Cheers,
KB