Re: [boost] C++11 Metaprogramming

Subject: Re: [boost] C++11 Metaprogramming
From: Dave Abrahams (dave_at_[hidden])
Date: 2012-04-07 11:18:00

on Fri Apr 06 2012, Sebastian Redl <sebastian.redl-AT-getdesigned.at> wrote:

>> Hm.  Can you describe this concept more fully, e.g. with a requirements
>> table or ConceptGCC syntax?
>
> concept Set<S, V> {
>   bool contains(const S&, const V&);
> }
>
> template <typename V>
> concept_map Set<std::set<V>, V> {
>   bool contains(const std::set<V>& s, const V& v) {
>     return s.find(v) != s.end();
>   }
> }
>
> template <typename V>
> concept_map Set<bool, V> {
>   bool contains(bool b, const V&) {
>     return b;
>   }
> }
>
> // various others, e.g. unordered_set.
>
> template <typename V, Callable<bool (V)> Fn>
> concept_map Set<Fn, V> {
>   bool contains(Fn fn, const V& v) {
>     return fn(v);
>   }
> }
>
> template <EqualityComparable V> if no other concept_map matches
> concept_map Set<V, V> {
>   bool contains(const V& s, const V& v) {
>     return s == v;
>   }
> }
>
> Specifically, I've used my is_callable to emulate the Callable concept
> in the enable_if of the contains() overload for functions, and the
> disable_if in the fallback version.

Thanks, that's very beautiful code.  I summarize as: this sort of
introspection is still useful for providing concept mappings.  That
makes sense, thanks.

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com