From: gotoken@... (GOTO Kentaro)
Date: 1999-05-17T16:12:27+09:00
Subject: [ruby-talk:00316] Re: Arity features for Proc object?

In message "[ruby-talk:00315] Re: Arity features for Proc object?"
    on 99/05/17, Yukihiro Matsumoto <matz@netlab.co.jp> writes:

>|Would it be possible to add arity feature to the Proc object.
>|So that one could easily determine  the required args  for a user passed
>|Proc in a function.
>
>Hmm, what is ARITY?  Does somebody know that word in Japanese??

Arity is (called `ariti-' in Japan :-) number of arguments. 
It is part of method signitures.  For example arity of `to_s' is 0, 
of `+' is 1, of `print' is variable...

>Is it the feature to determin whether a proc requires arguments?  Or
>the feature to retrieve the argument information (number, names,
>type)?
>
>I think the former is possible, the latter is ... I don't know.  I'm
>sure the latter is very hard even if possible.

I guess the former; I also don't understand why Proc does not
check number of arguments whareas any method do:

% ruby -e 'Proc.new{|i,j| p [i,j]}.call(1,2,3)'
[1, 2]
% ruby -e 'def a(i,j); p [i,j]; end; a(1,2,3)'
/tmp/rbMd8430:1:in `a': wrong # of arguments(3 for 2) (ArgumentError)
        from /tmp/rbMd8430:1

-- gotoken