type_traits.h revision a1eb50fe3d8213156c77ef2f7ae5c4ad629dbb95 
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// This is actually the conforming implementation which works with abstract
25// classes.  However, enough compilers have trouble with it that most will use
26// the one in boost/type_traits/object_traits.hpp. This implementation actually
27// works with VC7.0, but other interactions seem to fail when we use it.
28
29namespace llvm {
30
31namespace dont_use
32{
33    // These two functions should never be used. They are helpers to
34    // the is_class template below. They cannot be located inside
35    // is_class because doing so causes at least GCC to think that
36    // the value of the "value" enumerator is not constant. Placing
37    // them out here (for some strange reason) allows the sizeof
38    // operator against them to magically be constant. This is
39    // important to make the is_class<T>::value idiom zero cost. it
40    // evaluates to a constant 1 or 0 depending on whether the
41    // parameter T is a class or not (respectively).
42    template<typename T> char is_class_helper(void(T::*)());
43    template<typename T> double is_class_helper(...);
44}
45
46template <typename T>
47struct is_class
48{
49  // is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For
50  // more details:
51  // http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1
52 public:
53    enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) };
54};
55
56
57/// isPodLike - This is a type trait that is used to determine whether a given
58/// type can be copied around with memcpy instead of running ctors etc.
59template <typename T>
60struct isPodLike {
61  // If we don't know anything else, we can (at least) assume that all non-class
62  // types are PODs.
63  static const bool value = !is_class<T>::value;
64};
65
66// std::pair's are pod-like if their elements are.
67template<typename T, typename U>
68struct isPodLike<std::pair<T, U> > {
69  static const bool value = isPodLike<T>::value & isPodLike<U>::value;
70};
71
72
73template <class T, T v>
74struct integral_constant {
75  typedef T value_type;
76  static const value_type value = v;
77  typedef integral_constant<T,v> type;
78  operator value_type() { return value; }
79};
80
81typedef integral_constant<bool, true> true_type;
82typedef integral_constant<bool, false> false_type;
83
84/// \brief Metafunction that determines whether the two given types are
85/// equivalent.
86template<typename T, typename U> struct is_same       : public false_type {};
87template<typename T>             struct is_same<T, T> : public true_type {};
88
89/// \brief Metafunction that removes const qualification from a type.
90template <typename T> struct remove_const          { typedef T type; };
91template <typename T> struct remove_const<const T> { typedef T type; };
92
93/// \brief Metafunction that removes volatile qualification from a type.
94template <typename T> struct remove_volatile             { typedef T type; };
95template <typename T> struct remove_volatile<volatile T> { typedef T type; };
96
97/// \brief Metafunction that removes both const and volatile qualification from
98/// a type.
99template <typename T> struct remove_cv {
100  typedef typename remove_const<typename remove_volatile<T>::type>::type type;
101};
102
103/// \brief Helper to implement is_integral metafunction.
104template <typename T> struct is_integral_impl           : false_type {};
105template <> struct is_integral_impl<         bool>      : true_type {};
106template <> struct is_integral_impl<         char>      : true_type {};
107template <> struct is_integral_impl<  signed char>      : true_type {};
108template <> struct is_integral_impl<unsigned char>      : true_type {};
109template <> struct is_integral_impl<         wchar_t>   : true_type {};
110template <> struct is_integral_impl<         short>     : true_type {};
111template <> struct is_integral_impl<unsigned short>     : true_type {};
112template <> struct is_integral_impl<         int>       : true_type {};
113template <> struct is_integral_impl<unsigned int>       : true_type {};
114template <> struct is_integral_impl<         long>      : true_type {};
115template <> struct is_integral_impl<unsigned long>      : true_type {};
116template <> struct is_integral_impl<         long long> : true_type {};
117template <> struct is_integral_impl<unsigned long long> : true_type {};
118
119/// \brief Metafunction that determines whether the given type is an integral
120/// type.
121template <typename T>
122struct is_integral : is_integral_impl<T> {};
123
124/// \brief Metafunction that determines whether the given type is either an
125/// integral type or an enumeration type.
126///
127/// Note that this accepts potentially more integral types than we whitelist
128/// above for is_integral, it should accept essentially anything the compiler
129/// believes is an integral type.
130template <typename T> class is_integral_or_enum {
131
132  // Form a return type that can only be instantiated with an integral or enum
133  // types (or with nullptr_t in C++11).
134  template <typename U, U u = U()> struct check1_return_type { char c[2]; };
135  template <typename U> static check1_return_type<U> checker1(U*);
136  template <typename U> static char checker1(...);
137
138  // Form a return type that can only be instantiated with nullptr_t in C++11
139  // mode. It's harmless in C++98 mode, but this allows us to filter nullptr_t
140  // when building in C++11 mode without having to detect that mode for each
141  // different compiler.
142  struct nonce {};
143  template <typename U, nonce* u = U()>
144  struct check2_return_type { char c[2]; };
145  template <typename U> static check2_return_type<U> checker2(U*);
146  template <typename U> static char checker2(...);
147
148public:
149  enum {
150    value = (sizeof(char) != sizeof(checker1<T>(0)) &&
151             sizeof(char) == sizeof(checker2<T>(0)))
152  };
153};
154
155/// \brief Metafunction that determines whether the given type is a pointer
156/// type.
157template <typename T> struct is_pointer : false_type {};
158template <typename T> struct is_pointer<T*> : true_type {};
159
160// enable_if_c - Enable/disable a template based on a metafunction
161template<bool Cond, typename T = void>
162struct enable_if_c {
163  typedef T type;
164};
165
166template<typename T> struct enable_if_c<false, T> { };
167
168// enable_if - Enable/disable a template based on a metafunction
169template<typename Cond, typename T = void>
170struct enable_if : public enable_if_c<Cond::value, T> { };
171
172namespace dont_use {
173  template<typename Base> char base_of_helper(const volatile Base*);
174  template<typename Base> double base_of_helper(...);
175}
176
177/// is_base_of - Metafunction to determine whether one type is a base class of
178/// (or identical to) another type.
179template<typename Base, typename Derived>
180struct is_base_of {
181  static const bool value
182    = is_class<Base>::value && is_class<Derived>::value &&
183      sizeof(char) == sizeof(dont_use::base_of_helper<Base>((Derived*)0));
184};
185
186// remove_pointer - Metafunction to turn Foo* into Foo.  Defined in
187// C++0x [meta.trans.ptr].
188template <typename T> struct remove_pointer { typedef T type; };
189template <typename T> struct remove_pointer<T*> { typedef T type; };
190template <typename T> struct remove_pointer<T*const> { typedef T type; };
191template <typename T> struct remove_pointer<T*volatile> { typedef T type; };
192template <typename T> struct remove_pointer<T*const volatile> {
193    typedef T type; };
194
195template <bool, typename T, typename F>
196struct conditional { typedef T type; };
197
198template <typename T, typename F>
199struct conditional<false, T, F> { typedef F type; };
200
201}
202
203#endif
204