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From Martin Sebor <se...@roguewave.com>
Subject Re: implementation of Unary Traits
Date Tue, 01 Jul 2008 04:50:41 GMT
Travis Vitek wrote:
>  
[...]
> If you ask what I prefer, I'm going to tell you I prefer the second
> option (that is essentially what I wrote originally). But, honestly, for
> me to care either way, I need to know that there actually a noticeable
> performance difference between the two techniques.

FYI: I used gcc 4.3 and EDG eccp to measure the difference between
the compilation times of each of the two approaches (i.e., using
specialization vs using remove_cv).

In a program involving 10,000 invocations of is_void on distinct
types, the specialization approach was 5 and 10 times faster than
the one using remove_cv when using gcc and eccp, respectively. In
the same program using only 1000 types, the specialization solution
compiled 2 and 3 times faster, respectively.

With gcc, the compiler also required about half the amount of system
memory to compile the specialization-based solution than the other
one. (I didn't measure eccp memory usage).

This confirms that template metaprogramming is significantly more
costly in terms of system resources than alternative approaches,
at least in the gcc and eccp implementations. We should re-run the
same tests with other compilers to get a complete picture.

Martin


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