From: Ezra Zygmuntowicz <ezmobius@...>
Date: 2006-10-19T10:33:12+09:00
Subject: Re: whats this lambda code doing?


On Oct 18, 2006, at 6:15 PM, Ken Bloom wrote:

> On Thu, 19 Oct 2006 10:02:11 +0900, David Vallner wrote:
>
>> Ezra Zygmuntowicz wrote:
>>>    klasses.inject(block) do |blk, klass|
>>>      lambda { klass.with_scope(scope_hash, &blk) }
>>>    end.call
>>>
>>> That outer block that ends on end returns the lambda made inside  
>>> of that
>>> block. So end.call ends up being  lambda { klass.with_scope 
>>> (scope_hash,
>>> &blk) }.call
>>>
>>
>> Hmm. Unless I'm very mistaken, it would also only call the lambda for
>> the last object in klasses, generating several garbage (and  
>> relatively
>> expensive) lambdas. Boggle. Am I missing something?
>>
>> David Vallner
>
> This some wierd kind of lambda chaining. You're confusing "block" with
> "blk", so you're thinking that each version of this code is using the
> original block, but this is not so. Each lambda is chained to call the
> previous lambda. I haven't got a clue what with_scope does, but  
> this would
> all be a lot easier to understand if it was possible to eliminate the
> lambda, and deal with each class separately.
>
> -- 
> Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.


with_scope is an ActiveRecord thing for scoping your where clauses.  
It works like this:

Post.with_scope(:find => {:conditions => ["customer_id = ?",  
@customer.id]}) do
    @post = Post.find(:all)
end

And you can nest these with_scope blocks inside each other so the  
innermost #find method gets the scoped :conditions merged with its  
own conditions. So the original posters code is taking a list of  
Model classes and scoping the find and create calls on them to a  
specific blog.id .

But I have to agree that code is too clever for its own good.  
Twisting it up like that may make a golfer happy, the next guy to  
come across it will be confused when it could have been stated clearer.

Cheers.



-- Ezra Zygmuntowicz 
-- Lead Rails Evangelist
-- ez@engineyard.com
-- Engine Yard, Serious Rails Hosting
-- (866) 518-YARD (9273)