Re: Concepts in C++0x

From:

James Hopkin <tasjaevan@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Tue, 17 Apr 2007 09:38:46 CST

Message-ID:

<1176818468.835417.79610@o5g2000hsb.googlegroups.com>

On Apr 15, 6:08 pm, "Germ?n Diago" <germandi...@gmail.com> wrote:

The problem with my singleton concept is that I want my singleton to
have a static function MySingleton::instance(). The function must be
static. But I don't know how to express that kind of functionality.

The syntax should be:

  #include <concepts>
  auto concept Movable<typename T>
  {
    T::T(T&& t);
  }

  concept Singleton<typename T>
  requires !std::CopyConstructible<T>, !std::Assignable<T>, !
Movable<T>
  {
    static T& T::instance();
  }

and here's an example of a type (S) that models your concept:

  struct non_copyable
  {
    non_copyable() {}
  private:
    non_copyable(non_copyable&);
    non_copyable& operator=(non_copyable&);
  };

  struct S : non_copyable { static S& instance(); };
  concept_map Singleton<S> {}

  // syntax test:
  template <Singleton X> void f() { X& x = X::instance(); }

  int main()
  {
    f<S>();
  }

Currently, ConceptGCC seems to ignore the static in the concept: the
above compiles fine with or without it.

James

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