From: Jeremy McAnally <jeremymcanally@...>
Date: 2008-05-23T09:35:01+09:00
Subject: Re: lambda, ->, haskell, and so on

Even though I see the usefulness, that's just ugly.

--Jeremy

2008/5/22 Rados�aw Bu�at <radek.bulat@gmail.com>:
> On Thu, May 22, 2008 at 5:37 PM, Berger, Daniel <Daniel.Berger@qwest.com> wrote:
>> Could someone show me the use case for lambdas with default arguments?
>> Why would we need this in practice?
>>
>> I also don't understand the use case for blocks with default values.
>
> It's the same case as default values for regular method (functions).
> Lambdas, blocks are like anonymous functions (and closures).
> For example in ActiveRecord there is recently added new feature named_scope:
>
> class Post
>  named_scope :recent, lambda { |*args| {:conditions => ["released_at
>> ?", (args.first || 2.weeks.ago)]} }
> end
>
> usage:
>
> Post.recent # all posts from latest 2 weeks
> Post.recent(3.weeks.ago) # all posts from latest 3 weeks
>
> As you see there is very ugly trick with *args (because you can't just
> pust |time=2.weeks.ago| and for |time| there is warning when you don't
> put parameter).
>
> This example comes from Ryan Bates railscasts
> (http://railscasts.com/episodes/108).
> In Ruby 1.9 it's easier with ->
>
> named_scope :recent, ->(time = 2.weeks.ago) { {:conditions =>
> ["released_at > ?", time]} }
>
>
> --
> Rados�aw Bu�at
>
> http://radarek.jogger.pl - m�j blog
>



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