type_traits.h revision 239462
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 "llvm/Support/DataTypes.h" 21#include <cstddef> 22#include <utility> 23 24#ifndef __has_feature 25#define LLVM_DEFINED_HAS_FEATURE 26#define __has_feature(x) 0 27#endif 28 29// This is actually the conforming implementation which works with abstract 30// classes. However, enough compilers have trouble with it that most will use 31// the one in boost/type_traits/object_traits.hpp. This implementation actually 32// works with VC7.0, but other interactions seem to fail when we use it. 33 34namespace llvm { 35 36namespace dont_use 37{ 38 // These two functions should never be used. They are helpers to 39 // the is_class template below. They cannot be located inside 40 // is_class because doing so causes at least GCC to think that 41 // the value of the "value" enumerator is not constant. Placing 42 // them out here (for some strange reason) allows the sizeof 43 // operator against them to magically be constant. This is 44 // important to make the is_class<T>::value idiom zero cost. it 45 // evaluates to a constant 1 or 0 depending on whether the 46 // parameter T is a class or not (respectively). 47 template<typename T> char is_class_helper(void(T::*)()); 48 template<typename T> double is_class_helper(...); 49} 50 51template <typename T> 52struct is_class 53{ 54 // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For 55 // more details: 56 // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1 57 public: 58 enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) }; 59}; 60 61 62/// isPodLike - This is a type trait that is used to determine whether a given 63/// type can be copied around with memcpy instead of running ctors etc. 64template <typename T> 65struct isPodLike { 66#if __has_feature(is_trivially_copyable) 67 // If the compiler supports the is_trivially_copyable trait use it, as it 68 // matches the definition of isPodLike closely. 69 static const bool value = __is_trivially_copyable(T); 70#else 71 // If we don't know anything else, we can (at least) assume that all non-class 72 // types are PODs. 73 static const bool value = !is_class<T>::value; 74#endif 75}; 76 77// std::pair's are pod-like if their elements are. 78template<typename T, typename U> 79struct isPodLike<std::pair<T, U> > { 80 static const bool value = isPodLike<T>::value && isPodLike<U>::value; 81}; 82 83 84template <class T, T v> 85struct integral_constant { 86 typedef T value_type; 87 static const value_type value = v; 88 typedef integral_constant<T,v> type; 89 operator value_type() { return value; } 90}; 91 92typedef integral_constant<bool, true> true_type; 93typedef integral_constant<bool, false> false_type; 94 95/// \brief Metafunction that determines whether the two given types are 96/// equivalent. 97template<typename T, typename U> struct is_same : public false_type {}; 98template<typename T> struct is_same<T, T> : public true_type {}; 99 100/// \brief Metafunction that removes const qualification from a type. 101template <typename T> struct remove_const { typedef T type; }; 102template <typename T> struct remove_const<const T> { typedef T type; }; 103 104/// \brief Metafunction that removes volatile qualification from a type. 105template <typename T> struct remove_volatile { typedef T type; }; 106template <typename T> struct remove_volatile<volatile T> { typedef T type; }; 107 108/// \brief Metafunction that removes both const and volatile qualification from 109/// a type. 110template <typename T> struct remove_cv { 111 typedef typename remove_const<typename remove_volatile<T>::type>::type type; 112}; 113 114/// \brief Helper to implement is_integral metafunction. 115template <typename T> struct is_integral_impl : false_type {}; 116template <> struct is_integral_impl< bool> : true_type {}; 117template <> struct is_integral_impl< char> : true_type {}; 118template <> struct is_integral_impl< signed char> : true_type {}; 119template <> struct is_integral_impl<unsigned char> : true_type {}; 120template <> struct is_integral_impl< wchar_t> : true_type {}; 121template <> struct is_integral_impl< short> : true_type {}; 122template <> struct is_integral_impl<unsigned short> : true_type {}; 123template <> struct is_integral_impl< int> : true_type {}; 124template <> struct is_integral_impl<unsigned int> : true_type {}; 125template <> struct is_integral_impl< long> : true_type {}; 126template <> struct is_integral_impl<unsigned long> : true_type {}; 127template <> struct is_integral_impl< long long> : true_type {}; 128template <> struct is_integral_impl<unsigned long long> : true_type {}; 129 130/// \brief Metafunction that determines whether the given type is an integral 131/// type. 132template <typename T> 133struct is_integral : is_integral_impl<T> {}; 134 135/// \brief Metafunction to remove reference from a type. 136template <typename T> struct remove_reference { typedef T type; }; 137template <typename T> struct remove_reference<T&> { typedef T type; }; 138 139/// \brief Metafunction that determines whether the given type is a pointer 140/// type. 141template <typename T> struct is_pointer : false_type {}; 142template <typename T> struct is_pointer<T*> : true_type {}; 143template <typename T> struct is_pointer<T* const> : true_type {}; 144template <typename T> struct is_pointer<T* volatile> : true_type {}; 145template <typename T> struct is_pointer<T* const volatile> : true_type {}; 146 147/// \brief Metafunction that determines whether the given type is either an 148/// integral type or an enumeration type. 149/// 150/// Note that this accepts potentially more integral types than we whitelist 151/// above for is_integral because it is based on merely being convertible 152/// implicitly to an integral type. 153template <typename T> class is_integral_or_enum { 154 // Provide an overload which can be called with anything implicitly 155 // convertible to an unsigned long long. This should catch integer types and 156 // enumeration types at least. We blacklist classes with conversion operators 157 // below. 158 static double check_int_convertible(unsigned long long); 159 static char check_int_convertible(...); 160 161 typedef typename remove_reference<T>::type UnderlyingT; 162 static UnderlyingT &nonce_instance; 163 164public: 165 enum { 166 value = (!is_class<UnderlyingT>::value && !is_pointer<UnderlyingT>::value && 167 !is_same<UnderlyingT, float>::value && 168 !is_same<UnderlyingT, double>::value && 169 sizeof(char) != sizeof(check_int_convertible(nonce_instance))) 170 }; 171}; 172 173// enable_if_c - Enable/disable a template based on a metafunction 174template<bool Cond, typename T = void> 175struct enable_if_c { 176 typedef T type; 177}; 178 179template<typename T> struct enable_if_c<false, T> { }; 180 181// enable_if - Enable/disable a template based on a metafunction 182template<typename Cond, typename T = void> 183struct enable_if : public enable_if_c<Cond::value, T> { }; 184 185namespace dont_use { 186 template<typename Base> char base_of_helper(const volatile Base*); 187 template<typename Base> double base_of_helper(...); 188} 189 190/// is_base_of - Metafunction to determine whether one type is a base class of 191/// (or identical to) another type. 192template<typename Base, typename Derived> 193struct is_base_of { 194 static const bool value 195 = is_class<Base>::value && is_class<Derived>::value && 196 sizeof(char) == sizeof(dont_use::base_of_helper<Base>((Derived*)0)); 197}; 198 199// remove_pointer - Metafunction to turn Foo* into Foo. Defined in 200// C++0x [meta.trans.ptr]. 201template <typename T> struct remove_pointer { typedef T type; }; 202template <typename T> struct remove_pointer<T*> { typedef T type; }; 203template <typename T> struct remove_pointer<T*const> { typedef T type; }; 204template <typename T> struct remove_pointer<T*volatile> { typedef T type; }; 205template <typename T> struct remove_pointer<T*const volatile> { 206 typedef T type; }; 207 208template <bool, typename T, typename F> 209struct conditional { typedef T type; }; 210 211template <typename T, typename F> 212struct conditional<false, T, F> { typedef F type; }; 213 214} 215 216#ifdef LLVM_DEFINED_HAS_FEATURE 217#undef __has_feature 218#endif 219 220#endif 221