From: dblack@...
Date: 2007-09-09T17:28:16+09:00
Subject: Re: Bug in lambda?

Hi --

On Sun, 9 Sep 2007, kevin cline wrote:

> This looks like a pretty serious bug.  It seems that lambda-
> expressions are not properly localizing their formal arguments:
>
> bash-3.2$ ruby --version
> ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]
>
> bash-3.2$ cat lambda-bug.rb
> a = 0
> f = lambda { |a| a }
> puts "a = #{a}"
> puts "f.call(1) => #{f.call(1)}"
> puts "now a = #{a}"
>
> bash-3.2$ ruby lambda-bug.rb
> a = 0
> f.call(1) => 1
> now a = 1

Definitely not a bug. Block parameters use assignment semantics, with
regard to the scope in which the block appears. In your example,
you're assigning 1 to a. If you create a local variable inside the
block, however, it only exists for the duration of the block.

As far as remember, Guy Decoux and I are the only two people who think
that this makes perfect sense, once you learn it, and should not be
changed :-)


David

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