Gavin Kistner wrote:
> Because I just had to solve this problem in both JavaScript and Lua, and
> because I love Ruby more than either, I thought I'd ask people here how
> they'd solve it in Ruby.
>
> The general question is: how would do you associate a few object
> instances with methods on a per-method basis?
>
> The Situation/Requirements
> --------------------------
> A class has 2 different methods.
> Each method needs a couple 'scratch' objects to perform its
> calculations.
> The methods call each other; they must not use the same scratch objects.
> It is expensive to instantiate a scratch object.
> It's not expensive to initialize an existing scratch object with data.
> We like OOP coding, and want to call these as methods of a receiver.
>
> Wasteful Example:
> class Foo
>   def c1
>     tmp1 = ExpensiveObject.new
>     tmp2 = ExpensiveObject.new
>     # stuff involving tmp1/tmp2
>     result = tmp1 + tmp2 + c2
>   end
>   def c2
>     tmp1 = ExpensiveObject.new
>     tmp2 = ExpensiveObject.new
>     # stuff involving tmp1/tmp2
>     result = tmp1 + tmp2
>   end
> end

I look at this and think, "where the persistant locals?" Well, we don't
have em but they can be emulatated via instance vars.

 class Foo
   def c1
     tmp1 = (@_tmp1 ||= ExpensiveObject.new)
     tmp2 = (@_tmp2 ||= ExpensiveObject.new)
     # stuff involving tmp1/tmp2
     result = tmp1 + tmp2 + c2
   end
   def c2
     tmp1 = (@_tmp1 ||= ExpensiveObject.new)
     tmp2 = (@_tmp2 ||= ExpensiveObject.new)
     # stuff involving tmp1/tmp2
     result = tmp1 + tmp2
   end
 end

T.