type_traits.h revision 321369 
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 useful additions to the standard type_traits library.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_SUPPORT_TYPE_TRAITS_H
15#define LLVM_SUPPORT_TYPE_TRAITS_H
16
17#include "llvm/Support/Compiler.h"
18#include <type_traits>
19#include <utility>
20
21#ifndef __has_feature
22#define LLVM_DEFINED_HAS_FEATURE
23#define __has_feature(x) 0
24#endif
25
26namespace llvm {
27
28/// isPodLike - This is a type trait that is used to determine whether a given
29/// type can be copied around with memcpy instead of running ctors etc.
30template <typename T>
31struct isPodLike {
32  // std::is_trivially_copyable is available in libc++ with clang, libstdc++
33  // that comes with GCC 5.
34#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) ||      \
35    (defined(__GNUC__) && __GNUC__ >= 5)
36  // If the compiler supports the is_trivially_copyable trait use it, as it
37  // matches the definition of isPodLike closely.
38  static const bool value = std::is_trivially_copyable<T>::value;
39#elif __has_feature(is_trivially_copyable)
40  // Use the internal name if the compiler supports is_trivially_copyable but we
41  // don't know if the standard library does. This is the case for clang in
42  // conjunction with libstdc++ from GCC 4.x.
43  static const bool value = __is_trivially_copyable(T);
44#else
45  // If we don't know anything else, we can (at least) assume that all non-class
46  // types are PODs.
47  static const bool value = !std::is_class<T>::value;
48#endif
49};
50
51// std::pair's are pod-like if their elements are.
52template<typename T, typename U>
53struct isPodLike<std::pair<T, U>> {
54  static const bool value = isPodLike<T>::value && isPodLike<U>::value;
55};
56
57/// \brief Metafunction that determines whether the given type is either an
58/// integral type or an enumeration type, including enum classes.
59///
60/// Note that this accepts potentially more integral types than is_integral
61/// because it is based on being implicitly convertible to an integral type.
62/// Also note that enum classes aren't implicitly convertible to integral types,
63/// the value may therefore need to be explicitly converted before being used.
64template <typename T> class is_integral_or_enum {
65  using UnderlyingT = typename std::remove_reference<T>::type;
66
67public:
68  static const bool value =
69      !std::is_class<UnderlyingT>::value && // Filter conversion operators.
70      !std::is_pointer<UnderlyingT>::value &&
71      !std::is_floating_point<UnderlyingT>::value &&
72      (std::is_enum<UnderlyingT>::value ||
73       std::is_convertible<UnderlyingT, unsigned long long>::value);
74};
75
76/// \brief If T is a pointer, just return it. If it is not, return T&.
77template<typename T, typename Enable = void>
78struct add_lvalue_reference_if_not_pointer { using type = T &; };
79
80template <typename T>
81struct add_lvalue_reference_if_not_pointer<
82    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
83  using type = T;
84};
85
86/// \brief If T is a pointer to X, return a pointer to const X. If it is not,
87/// return const T.
88template<typename T, typename Enable = void>
89struct add_const_past_pointer { using type = const T; };
90
91template <typename T>
92struct add_const_past_pointer<
93    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
94  using type = const typename std::remove_pointer<T>::type *;
95};
96
97template <typename T, typename Enable = void>
98struct const_pointer_or_const_ref {
99  using type = const T &;
100};
101template <typename T>
102struct const_pointer_or_const_ref<
103    T, typename std::enable_if<std::is_pointer<T>::value>::type> {
104  using type = typename add_const_past_pointer<T>::type;
105};
106
107} // end namespace llvm
108
109// If the compiler supports detecting whether a class is final, define
110// an LLVM_IS_FINAL macro. If it cannot be defined properly, this
111// macro will be left undefined.
112#if __cplusplus >= 201402L
113#define LLVM_IS_FINAL(Ty) std::is_final<Ty>()
114#elif __has_feature(is_final) || LLVM_GNUC_PREREQ(4, 7, 0)
115#define LLVM_IS_FINAL(Ty) __is_final(Ty)
116#endif
117
118#ifdef LLVM_DEFINED_HAS_FEATURE
119#undef __has_feature
120#endif
121
122#endif // LLVM_SUPPORT_TYPE_TRAITS_H
123