On 27/09/2010 23:01, David Abrahams wrote:
At Mon, 27 Sep 2010 22:01:09 +0100, Mathias Gaunard wrote:
On 27/09/2010 17:56, David Abrahams wrote:
Among other things, you're missing the other half of concept checking: checking algorithm bodies against constraints (which is done in the Concept_check library by using archetypes).
P.S. I'm not claiming concepts can't be described via valid expressions; I'm claiming it's the wrong approach, for reasons that should become evident to anyone who *actually does the exercise*.
I don't see how a set of statements is much different from a set of expressions, except that statements don't have nice properties from a meta-programming point of view.
No comment.
do-the-exercise-ly y'rs,
I've done it and there was no particular problem. I just need to check the argument are input iterators and an unary function object taking the same value as the iterator value type and returning a boolean. (of course, by taking a particular value, I really mean taking something that can be converted from that particular value, and by returning a particular value I mean returning a type convertible to that value, but all of those implicit conversions are taken care of automatically by expressions) The concept definitions of iterators and function objects are already defined in terms of valid expressions anyway, each having particular semantics. Are you maybe hinting at a trick to properly ensure input iterators and not just forward ones? Also, I don't think replacing statements by expressions means we should get rid of archetypes at all. They're still required if you want to actually instantiate the template and test the code, rather than just test that the arguments match what you expect. Checking the arguments match what you expect is the important bit for good error messages and validation, while archetypes are really useful for development to check your code and your requirements are consistent by ensuring it works with the minimal amount of requirements. All in all, ConceptCheck isn't so bad: we just need to replace the main body of statements by a compile-time itereable and manipulable list of expressions.