1 //===- llvm/Support/type_traits.h - Simplfied type traits -------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 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. 14 // 15 //===----------------------------------------------------------------------===// 16 17 #ifndef LLVM_SUPPORT_TYPE_TRAITS_H 18 #define LLVM_SUPPORT_TYPE_TRAITS_H 19 20 #include <utility> 21 22 // This is actually the conforming implementation which works with abstract 23 // classes. However, enough compilers have trouble with it that most will use 24 // the one in boost/type_traits/object_traits.hpp. This implementation actually 25 // works with VC7.0, but other interactions seem to fail when we use it. 26 27 namespace llvm { 28 29 namespace dont_use 30 { 31 // These two functions should never be used. They are helpers to 32 // the is_class template below. They cannot be located inside 33 // is_class because doing so causes at least GCC to think that 34 // the value of the "value" enumerator is not constant. Placing 35 // them out here (for some strange reason) allows the sizeof 36 // operator against them to magically be constant. This is 37 // important to make the is_class<T>::value idiom zero cost. it 38 // evaluates to a constant 1 or 0 depending on whether the 39 // parameter T is a class or not (respectively). 40 template<typename T> char is_class_helper(void(T::*)()); 41 template<typename T> double is_class_helper(...); 42 } 43 44 template <typename T> 45 struct is_class 46 { 47 // is_class<> metafunction due to Paul Mensonides (leavings (at) attbi.com). For 48 // more details: 49 // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1 50 public: 51 enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) }; 52 }; 53 54 55 /// isPodLike - This is a type trait that is used to determine whether a given 56 /// type can be copied around with memcpy instead of running ctors etc. 57 template <typename T> 58 struct isPodLike { 59 // If we don't know anything else, we can (at least) assume that all non-class 60 // types are PODs. 61 static const bool value = !is_class<T>::value; 62 }; 63 64 // std::pair's are pod-like if their elements are. 65 template<typename T, typename U> 66 struct isPodLike<std::pair<T, U> > { 67 static const bool value = isPodLike<T>::value & isPodLike<U>::value; 68 }; 69 70 71 /// \brief Metafunction that determines whether the two given types are 72 /// equivalent. 73 template<typename T, typename U> 74 struct is_same { 75 static const bool value = false; 76 }; 77 78 template<typename T> 79 struct is_same<T, T> { 80 static const bool value = true; 81 }; 82 83 // enable_if_c - Enable/disable a template based on a metafunction 84 template<bool Cond, typename T = void> 85 struct enable_if_c { 86 typedef T type; 87 }; 88 89 template<typename T> struct enable_if_c<false, T> { }; 90 91 // enable_if - Enable/disable a template based on a metafunction 92 template<typename Cond, typename T = void> 93 struct enable_if : public enable_if_c<Cond::value, T> { }; 94 95 namespace dont_use { 96 template<typename Base> char base_of_helper(const volatile Base*); 97 template<typename Base> double base_of_helper(...); 98 } 99 100 /// is_base_of - Metafunction to determine whether one type is a base class of 101 /// (or identical to) another type. 102 template<typename Base, typename Derived> 103 struct is_base_of { 104 static const bool value 105 = is_class<Base>::value && is_class<Derived>::value && 106 sizeof(char) == sizeof(dont_use::base_of_helper<Base>((Derived*)0)); 107 }; 108 109 // remove_pointer - Metafunction to turn Foo* into Foo. Defined in 110 // C++0x [meta.trans.ptr]. 111 template <typename T> struct remove_pointer { typedef T type; }; 112 template <typename T> struct remove_pointer<T*> { typedef T type; }; 113 template <typename T> struct remove_pointer<T*const> { typedef T type; }; 114 template <typename T> struct remove_pointer<T*volatile> { typedef T type; }; 115 template <typename T> struct remove_pointer<T*const volatile> { 116 typedef T type; }; 117 118 template <bool, typename T, typename F> 119 struct conditional { typedef T type; }; 120 121 template <typename T, typename F> 122 struct conditional<false, T, F> { typedef F type; }; 123 124 } 125 126 #endif 127
