From: Dominik Bathon <dbatml@...>
Date: 2005-08-07T12:19:10+09:00
Subject: Re: new block notation (was: Re: ruby-dev summary 26468-26661)

On Sun, 07 Aug 2005 02:11:07 +0200, Trans <transfire@gmail.com> wrote:

>  > IIUC the point is that arguments given to a (future) lambda will act
>> like in a method definition, while in a block they behave slightly
>> differently
>
> Please continue.

I think somewhere in this thread I read that block/current lambda  
arguments are handled like multiple assignment and this seems to be true:

>> b = lambda { |a| p a }
=> #<Proc:0xb7eec5ec@(irb):1>
>> b[]
(irb):1: warning: multiple values for a block parameter (0 for 1)
         from (irb):2
nil
=> nil
>> b[nil]
nil
=> nil
>> b[1,2,3]
(irb):1: warning: multiple values for a block parameter (3 for 1)
         from (irb):4
[1, 2, 3]
=> nil
>> a = nil
=> nil
>> a = 1,2,3
=> [1, 2, 3]

So you get warnings that there is the wrong number of arguments but it  
works nonetheless.

If I understood this thread correct the future lambdas won't allow a wrong  
number of arguments (like methods today), while blocks will still do.

So, I think

(-> (a) { p a })[]

and

(-> (a) { p a })[1, 2, 3]

would give errors instead of warnings.

I just experimented and found the following:

>> d = lambda { |a,b| b ||= "default"; p a, b }
=> #<Proc:0xb7edea78@(irb):8>
>> d[1]
ArgumentError: wrong number of arguments (1 for 2)
         from (irb):8
         from (irb):8:in `[]'
         from (irb):9

but:

>> [1,2].each { |a,b| b ||= "default"; p a, b }
1
"default"
2
"default"
=> [1, 2]

This is in 1.8. So some of those checks are there already.

Dominik