From: David Vallner <david@...>
Date: 2006-01-12T11:05:55+09:00
Subject: Re: Looking up properties and speed

Jonathan Leighton wrote:

>Hi,
>
>In Javascript, if one were to use the same property value twice or more,
>one would store it in a local variable because looking up the property
>slows things down.
>
>Is the situation the same in Ruby? Is there any speed difference between
>these:
>
>def foo
>  val = obj.prop
>  puts val
>  puts val
>end
>
>def boo
>  puts obj.prop
>  puts obj.prop
>end
>
>I assume not because I think the reason it's like that with Javascript
>is because of the DOM (yeah, that's not strictly Javascript).
>
>Cheers
>
>  
>
Hmm. Accessing the property should be slower, because it involves a 
method call.

<rant>
BUT! Quite a few guides on coding style would say temporary variables 
should be avoided whenever possible in clean OO code and replaced with 
queries (computed property getters). And using a temporary variable only 
to cheat the interpreter is plain wrong. Avoid. The speed improvement 
you gain will most likely be next to insignificant, and if not, you 
still should never optimize without profiling the code first.

That said, the code you show is more likely to end up refactored as a 
method of ``obj'', where you could access the instance variable 
directly. A method that only manipulates data on another object indeed 
should be a method of that object.

Suggested reading: Martin Fowler's "Refactoring...", a timeless, and IMO 
highly respected classic.
</rant>

David