1 //===- llvm/Support/type_traits.h - Simplfied type traits -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file provides a template class that determines if a type is a class or
11 // not. The basic mechanism, based on using the pointer to member function of
12 // a zero argument to a function was "boosted" from the boost type_traits
13 // library. See http://www.boost.org/ for all the gory details.
15 //===----------------------------------------------------------------------===//
17 #ifndef LLVM_SUPPORT_TYPE_TRAITS_H
18 #define LLVM_SUPPORT_TYPE_TRAITS_H
20 // This is actually the conforming implementation which works with abstract
21 // classes. However, enough compilers have trouble with it that most will use
22 // the one in boost/type_traits/object_traits.hpp. This implementation actually
23 // works with VC7.0, but other interactions seem to fail when we use it.
29 // These two functions should never be used. They are helpers to
30 // the is_class template below. They cannot be located inside
31 // is_class because doing so causes at least GCC to think that
32 // the value of the "value" enumerator is not constant. Placing
33 // them out here (for some strange reason) allows the sizeof
34 // operator against them to magically be constant. This is
35 // important to make the is_class<T>::value idiom zero cost. it
36 // evaluates to a constant 1 or 0 depending on whether the
37 // parameter T is a class or not (respectively).
38 template<typename T> char is_class_helper(void(T::*)(void));
39 template<typename T> double is_class_helper(...);
45 // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For
47 // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1
49 enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) };