From: Bob Hutchison <hutch@...>
Date: 2006-07-24T01:19:39+09:00
Subject: Re: [ANN] Mongoose 0.2.0

Hi,

On Jul 21, 2006, at 11:10 PM, John W. Long wrote:

> Jamey Cribbs wrote:
>> The way it works is that in the Plane.find method, I grab the  
>> block and pass it to #instance_eval.  This executes the block in  
>> the Plane classes environment, so it knows that when it sees the  
>> attribute "speed" or "country" in the block, it knows to call  
>> Plane.speed and Plane.country.  Planes.speed happens to be a  
>> reference to a SkiplistColumn instance and it knows how to handle  
>> the "> 350" passed to it.
>
> The problem with this approach is that you loose access to instance  
> variables. For instance:
>
>   >> class Object
>   >>   def with(&block)
>   >>     instance_eval(&block)
>   >>   end
>   >> end
>   => nil
>   >> @test = 1
>   => 1
>   >> Object.new.with { puts @test }
>   => nil
>
> In the above example @test when used within the context of the with  
> block is thought to be an instance variable of the object, which is  
> why it returns nil instead of 1. I consider this behavior undesirable.


Is this really a problem? If we write it this way:

class Object
   def with(&block)
     instance_eval(&block)
   end
end

class Toy
   def play
     @test = 'hello there'
     with { puts "!!!! [#{@test}] !!!!" }
   end
end

toy = Toy.new
toy.play

you get the output:

!!!! [hello there] !!!!

which is using the @test as I think you want.

Cheers,
Bob


>
> --
> John Long
> http://wiseheartdesign.com
>

----
Bob Hutchison                  -- blogs at <http://www.recursive.ca/ 
hutch/>
Recursive Design Inc.          -- <http://www.recursive.ca/>
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