From: Robert Klemme <shortcutter@...>
Date: 2006-08-02T22:13:45+09:00
Subject: Re: Different semantics of Proc and method call -- bug or feature?

Tammo Freese wrote:
> Hi all,
> 
> 
> I stumbled over the following difference between method calls and Proc 
> calls:
> 
> require 'pp';
> 
> def a_method(arg, *args)
>   arg
> end
> 
> a_proc = Proc.new do | arg, *args |
>   arg
> end
> 
> pp a_method(1)       # => expected 1, got 1
> pp a_proc.call(1)    # => expected 1, got 1
> 
> pp a_method([1])     # => expected [1], got [1]
> pp a_proc.call([1])  # => expected [1], got 1     <== ?!
> 
> 
> I would expect that method calls and proc calls do not differ in such a 
> way.
> Is this a bug or a feature?

I think it's rather a feature although I can understand your surprise. 
IIRC block (and thus proc) parameters behave more similar to assignments:

 >> def t
 >> yield 1
 >> yield [2]
 >> yield [3,4]
 >> end
=> nil
 >> t {|a| p a}
1
[2]
[3, 4]
=> nil
 >> t {|a,*b| p a}
1
2
3
=> nil
 >> t {|a,| p a}
1
2
3
=> nil

15:04:11 [~]: ruby -e 'a=1; p a; a=[2,3]; p a'
1
[2, 3]
15:04:45 [~]: ruby -e 'a=1; p a; a=[2]; p a; a=[3,4]; p a'
1
[2]
[3, 4]
15:05:08 [~]: ruby -e 'a,*b=1; p a; a,*b=[2]; p a; a,*b=[3,4]; p a'
1
2
3
15:05:25 [~]: ruby -e 'a,=1; p a; a,=[2]; p a; a,=[3,4]; p a'
1
2
3
15:05:34 [~]:

HTH

Kind regards

	robert