type_traits.h revision 198396
1259698Sdim//===- llvm/Support/type_traits.h - Simplfied type traits -------*- C++ -*-===// 2259698Sdim// 3259698Sdim// The LLVM Compiler Infrastructure 4259698Sdim// 5259698Sdim// This file is distributed under the University of Illinois Open Source 6259698Sdim// License. See LICENSE.TXT for details. 7259698Sdim// 8259698Sdim//===----------------------------------------------------------------------===// 9259698Sdim// 10259698Sdim// This file provides a template class that determines if a type is a class or 11259698Sdim// not. The basic mechanism, based on using the pointer to member function of 12259698Sdim// a zero argument to a function was "boosted" from the boost type_traits 13259698Sdim// library. See http://www.boost.org/ for all the gory details. 14259698Sdim// 15259698Sdim//===----------------------------------------------------------------------===// 16259698Sdim 17259698Sdim#ifndef LLVM_SUPPORT_TYPE_TRAITS_H 18259698Sdim#define LLVM_SUPPORT_TYPE_TRAITS_H 19259698Sdim 20259698Sdim// This is actually the conforming implementation which works with abstract 21259698Sdim// classes. However, enough compilers have trouble with it that most will use 22259698Sdim// the one in boost/type_traits/object_traits.hpp. This implementation actually 23259698Sdim// works with VC7.0, but other interactions seem to fail when we use it. 24259698Sdim 25259698Sdimnamespace llvm { 26259698Sdim 27259698Sdimnamespace dont_use 28259698Sdim{ 29259698Sdim // These two functions should never be used. They are helpers to 30259698Sdim // the is_class template below. They cannot be located inside 31259698Sdim // is_class because doing so causes at least GCC to think that 32259698Sdim // the value of the "value" enumerator is not constant. Placing 33259698Sdim // them out here (for some strange reason) allows the sizeof 34259698Sdim // operator against them to magically be constant. This is 35259698Sdim // important to make the is_class<T>::value idiom zero cost. it 36259698Sdim // evaluates to a constant 1 or 0 depending on whether the 37259698Sdim // parameter T is a class or not (respectively). 38259698Sdim template<typename T> char is_class_helper(void(T::*)()); 39259698Sdim template<typename T> double is_class_helper(...); 40259698Sdim} 41259698Sdim 42259698Sdimtemplate <typename T> 43259698Sdimstruct is_class 44259698Sdim{ 45259698Sdim // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For 46259698Sdim // more details: 47259698Sdim // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1 48259698Sdim public: 49259698Sdim enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) }; 50259698Sdim}; 51259698Sdim 52259698Sdim/// \brief Metafunction that determines whether the two given types are 53259698Sdim/// equivalent. 54259698Sdimtemplate<typename T, typename U> 55259698Sdimstruct is_same { 56259698Sdim static const bool value = false; 57259698Sdim}; 58259698Sdim 59259698Sdimtemplate<typename T> 60259698Sdimstruct is_same<T, T> { 61259698Sdim static const bool value = true; 62259698Sdim}; 63259698Sdim 64259698Sdim// enable_if_c - Enable/disable a template based on a metafunction 65259698Sdimtemplate<bool Cond, typename T = void> 66259698Sdimstruct enable_if_c { 67259698Sdim typedef T type; 68259698Sdim}; 69259698Sdim 70259698Sdimtemplate<typename T> struct enable_if_c<false, T> { }; 71259698Sdim 72259698Sdim// enable_if - Enable/disable a template based on a metafunction 73259698Sdimtemplate<typename Cond, typename T = void> 74259698Sdimstruct enable_if : public enable_if_c<Cond::value, T> { }; 75259698Sdim 76259698Sdimnamespace dont_use { 77259698Sdim template<typename Base> char base_of_helper(const volatile Base*); 78259698Sdim template<typename Base> double base_of_helper(...); 79259698Sdim} 80259698Sdim 81259698Sdim/// is_base_of - Metafunction to determine whether one type is a base class of 82259698Sdim/// (or identical to) another type. 83259698Sdimtemplate<typename Base, typename Derived> 84259698Sdimstruct is_base_of { 85259698Sdim static const bool value 86259698Sdim = is_class<Base>::value && is_class<Derived>::value && 87259698Sdim sizeof(char) == sizeof(dont_use::base_of_helper<Base>((Derived*)0)); 88259698Sdim}; 89259698Sdim 90259698Sdim// remove_pointer - Metafunction to turn Foo* into Foo. Defined in 91259698Sdim// C++0x [meta.trans.ptr]. 92259698Sdimtemplate <typename T> struct remove_pointer { typedef T type; }; 93259698Sdimtemplate <typename T> struct remove_pointer<T*> { typedef T type; }; 94259698Sdimtemplate <typename T> struct remove_pointer<T*const> { typedef T type; }; 95259698Sdimtemplate <typename T> struct remove_pointer<T*volatile> { typedef T type; }; 96259698Sdimtemplate <typename T> struct remove_pointer<T*const volatile> { 97259698Sdim typedef T type; }; 98259698Sdim 99259698Sdim} 100259698Sdim 101259698Sdim#endif 102259698Sdim