From: Robert Klemme <bob.news@...>
Date: 2006-03-29T03:59:06+09:00
Subject: Re: New Optimization idea.

John Carter wrote:
> I have a couple of classes like so...
> 
> class Foo
>   def step1
>     @mine = Hash.new
>     # Perhaps stuff things into @mine
>   end
> 
>   def step2
>     @mine.each_pair do |key,value|
>       # Do stuff
>     end
>   end
> end
> 
> Profiling with my "new" profiler shows that I'm creating many many Hash 
> objects, probably way more than I need. In fact most of them are empty.
> 
> Optimization trick...
> 
> 
> class Object
>   FROZEN_EMPTY_HASH = Hash.new.freeze
> end
> 
> class Foo
>   @@hash_cache = Hash.new
> 
>   def step1
>     @mine = @@hash_cache
>     # Perhaps stuff things into @mine
>     if @mine.empty?
>       @mine = FROZEN_EMPTY_HASH
>     else
>       @@hash_cache = Hash.new
>     end
>   end
> 
>   def step2
>     @mine.each_pair do |key,value|
>       # Do stuff
>     end
>   end
> end

You could as well leave the member nil and change the getter appropriately:

class Foo
   def mine() @mine || FROZEN_EMPTY_HASH end
   def step2() mine.each_pair ...
end

Or do the test in step2...
@mine and @mine.each_pair ...

Kind regards

	robert