From: Dan Sugalski <dan@...>
Date: 2003-01-06T11:15:48+09:00
Subject: Re: Compile time constant folding?

At 10:32 AM +0900 1/6/03, Joel VanderWerf wrote:
>Dan Sugalski wrote:
>>It's not like this is expensive in the simple case, but when you do 
>>something like:
>>
>>    (1 / sin(2.3)) * log(4)
>>
>>in a loop, well, that can add up pretty quickly.
>
>And in this case we have to assume that sin and log are pure 
>functions, in addition to assuming that they will never be 
>redefined. Sure, you can make sin and log special cases, but where 
>do you stop?

Never! Never I say--first constant expressions, next the world! 
Bwahahahahaha! Erm. Sorry, nevermind... :)

>Anyway, why would one have such a complex expression within a loop?

It's not uncommon to have expressions that look non-constant that 
turn out to really be constant once surrounding code's analyzed.

>  It's not like in C where an apparently simple expression can be 
>expanded by the preprocessor into something that needs a lot of 
>folding. The complexity of the expression is apparent in the ruby 
>code, and it is telling you to move it out of the loop.

You'd be surprised. Anyway, Matz's spoken, so I'm set now.
-- 
                                         Dan

--------------------------------------"it's like this"-------------------
Dan Sugalski                          even samurai
dan@sidhe.org                         have teddy bears and even
                                       teddy bears get drunk