Re: [Boost-users] C++ guru required!

Daryle Walker wrote:

From:ramey@rrsd.com Date:Fri, 17 Feb 2012 12:40:12 -0800 I've got a really dumb question. My question is illustrated by the followingcode snippet.

templateT inline operator%(const T & lhs, const U & rhs) { if(0 == rhs) throw std::domain_error("Divide by zero"); if(boost::is_same::value && boost::numeric::is_signed<U>::value ){ if(1 == rhs || -1 == rhs) // is this dropped? overflow("unsigned type can hold this result"); } return lhs % rhs;} I would like to think that the second if is alwaysdropped from the compile for a particular pairof types since this can be evaluated at compile time. If I'm correct, I can replace some tedioustemplate metaprogramming for some straightforwardand transparent code inserted in a convenient codeinserted in the most convenient place. Andre Alex... gave a talk at "Going Native" proposinga "static if" for this case. But I don't see the necessity forfor this since I would assume that the compilerjust optimises away the "dead" code. I've compiledthe above and it seems to do what I want butstill I wonder. Basically I see lots of applications of variationson this idea to get the benefits of tmp withoutthe attendent pain. Am I missing anything here?

If you want to (partially) specialize on types, then use a class template that can act as a function object (i.e. has an operator ()). I was going to leave at that, but I see some other problems.

Hmmm - this doesn't answer my question. My question is: is there any reason that my example is a bad idea. It works as I expect and is the equivalent of the TMP solution (assuming that the C++ compiler eliminates dead code - which is presumed to be widely implemented though not required by the standard.) To me it yields all the benefits detailed in Andrei's proposal for "static if". The only problem I have with it is that it depends upon widely implemented behavior which is not required by the standard. questions: a) is this a problem? b) are there any other problems which I haven't noticed? Robert Ramey