From: Joel VanderWerf <vjoel@...>
Date: 2008-04-18T06:58:44+09:00
Subject: Re: When are lambdas needed?

Avdi Grimm wrote:
> On Thu, Apr 17, 2008 at 5:35 PM, Stedwick <philip.brocoum@gmail.com> wrote:
>>  Can somebody give me an extremely useful, NOT complicated, example of
>>  when lambdas are the absolute perfect solution to a problem?
> 
> Every time you use a block in ruby you're using a lambda implicitly.

Implicitly, but not really. I wonder, was the original question more 
like "what are blocks for?" or "yes, I know what blocks are for, but why 
are there also these Proc objects, which are instantiated with the 
lambda construct?"

If the latter, then one answer is: when you need the program state that 
is encapsulated in a block to persist outside of the method in which it 
is used. For example, this happens in event-based frameworks: a setup 
method in a client class registers lambdas as event handlers; the 
framework doesn't need to know the classes or methods of the client 
class, hence loose coupling. As a bonus, these handlers can refer to 
shared program state (local variables) in the setup method.

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407