base/tuple.h

   1 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 // A Tuple is a generic templatized container, similar in concept to std::pair
   6 // and std::tuple.  The convenient MakeTuple() function takes any number of
   7 // arguments and will construct and return the appropriate Tuple object.  The
   8 // functions DispatchToMethod and DispatchToFunction take a function pointer or
   9 // instance and method pointer, and unpack a tuple into arguments to the call.
  10 //
  11 // Tuple elements are copied by value, and stored in the tuple.  See the unit
  12 // tests for more details of how/when the values are copied.
  13 //
  14 // Example usage:
  15 //   // These two methods of creating a Tuple are identical.
  16 //   Tuple<int, const char*> tuple_a(1, "wee");
  17 //   Tuple<int, const char*> tuple_b = MakeTuple(1, "wee");
  18 //
  19 //   void SomeFunc(int a, const char* b) { }
  20 //   DispatchToFunction(&SomeFunc, tuple_a);  // SomeFunc(1, "wee")
  21 //   DispatchToFunction(
  22 //       &SomeFunc, MakeTuple(10, "foo"));    // SomeFunc(10, "foo")
  23 //
  24 //   struct { void SomeMeth(int a, int b, int c) { } } foo;
  25 //   DispatchToMethod(&foo, &Foo::SomeMeth, MakeTuple(1, 2, 3));
  26 //   // foo->SomeMeth(1, 2, 3);
  27
  28 #ifndef BASE_TUPLE_H__
  29 #define BASE_TUPLE_H__
  30
  31 #include "base/bind_helpers.h"
  32
  33 // Index sequences
  34 //
  35 // Minimal clone of the similarly-named C++14 functionality.
  36
  37 template <size_t...>
  38 struct IndexSequence {};
  39
  40 template <size_t... Ns>
  41 struct MakeIndexSequenceImpl;
  42
  43 #if defined(_PREFAST_) && defined(OS_WIN)
  44
  45 // Work around VC++ 2013 /analyze internal compiler error:
  46 // https://connect.microsoft.com/VisualStudio/feedback/details/1053626
  47
  48 template <> struct MakeIndexSequenceImpl<0> {
  49   using Type = IndexSequence<>;
  50 };
  51 template <> struct MakeIndexSequenceImpl<1> {
  52   using Type = IndexSequence<0>;
  53 };
  54 template <> struct MakeIndexSequenceImpl<2> {
  55   using Type = IndexSequence<0,1>;
  56 };
  57 template <> struct MakeIndexSequenceImpl<3> {
  58   using Type = IndexSequence<0,1,2>;
  59 };
  60 template <> struct MakeIndexSequenceImpl<4> {
  61   using Type = IndexSequence<0,1,2,3>;
  62 };
  63 template <> struct MakeIndexSequenceImpl<5> {
  64   using Type = IndexSequence<0,1,2,3,4>;
  65 };
  66 template <> struct MakeIndexSequenceImpl<6> {
  67   using Type = IndexSequence<0,1,2,3,4,5>;
  68 };
  69 template <> struct MakeIndexSequenceImpl<7> {
  70   using Type = IndexSequence<0,1,2,3,4,5,6>;
  71 };
  72 template <> struct MakeIndexSequenceImpl<8> {
  73   using Type = IndexSequence<0,1,2,3,4,5,6,7>;
  74 };
  75 template <> struct MakeIndexSequenceImpl<9> {
  76   using Type = IndexSequence<0,1,2,3,4,5,6,7,8>;
  77 };
  78 template <> struct MakeIndexSequenceImpl<10> {
  79   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9>;
  80 };
  81 template <> struct MakeIndexSequenceImpl<11> {
  82   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10>;
  83 };
  84
  85 #else  // defined(WIN) && defined(_PREFAST_)
  86
  87 template <size_t... Ns>
  88 struct MakeIndexSequenceImpl<0, Ns...> {
  89   using Type = IndexSequence<Ns...>;
  90 };
  91
  92 template <size_t N, size_t... Ns>
  93 struct MakeIndexSequenceImpl<N, Ns...>
  94     : MakeIndexSequenceImpl<N - 1, N - 1, Ns...> {};
  95
  96 #endif  // defined(WIN) && defined(_PREFAST_)
  97
  98 template <size_t N>
  99 using MakeIndexSequence = typename MakeIndexSequenceImpl<N>::Type;
 100
 101 // Traits ----------------------------------------------------------------------
 102 //
 103 // A simple traits class for tuple arguments.
 104 //
 105 // ValueType: the bare, nonref version of a type (same as the type for nonrefs).
 106 // RefType: the ref version of a type (same as the type for refs).
 107 // ParamType: what type to pass to functions (refs should not be constified).
 108
 109 template <class P>
 110 struct TupleTraits {
 111   typedef P ValueType;
 112   typedef P& RefType;
 113   typedef const P& ParamType;
 114 };
 115
 116 template <class P>
 117 struct TupleTraits<P&> {
 118   typedef P ValueType;
 119   typedef P& RefType;
 120   typedef P& ParamType;
 121 };
 122
 123 // Tuple -----------------------------------------------------------------------
 124 //
 125 // This set of classes is useful for bundling 0 or more heterogeneous data types
 126 // into a single variable.  The advantage of this is that it greatly simplifies
 127 // function objects that need to take an arbitrary number of parameters; see
 128 // RunnableMethod and IPC::MessageWithTuple.
 129 //
 130 // Tuple<> is supplied to act as a 'void' type.  It can be used, for example,
 131 // when dispatching to a function that accepts no arguments (see the
 132 // Dispatchers below).
 133 // Tuple<A> is rarely useful.  One such use is when A is non-const ref that you
 134 // want filled by the dispatchee, and the tuple is merely a container for that
 135 // output (a "tier").  See MakeRefTuple and its usages.
 136
 137 template <typename IxSeq, typename... Ts>
 138 struct TupleBaseImpl;
 139 template <typename... Ts>
 140 using TupleBase = TupleBaseImpl<MakeIndexSequence<sizeof...(Ts)>, Ts...>;
 141 template <size_t N, typename T>
 142 struct TupleLeaf;
 143
 144 template <typename... Ts>
 145 struct Tuple : TupleBase<Ts...> {
 146   Tuple() : TupleBase<Ts...>() {}
 147   explicit Tuple(typename TupleTraits<Ts>::ParamType... args)
 148       : TupleBase<Ts...>(args...) {}
 149 };
 150
 151 // Avoids ambiguity between Tuple's two constructors.
 152 template <>
 153 struct Tuple<> {};
 154
 155 template <size_t... Ns, typename... Ts>
 156 struct TupleBaseImpl<IndexSequence<Ns...>, Ts...> : TupleLeaf<Ns, Ts>... {
 157   TupleBaseImpl() : TupleLeaf<Ns, Ts>()... {}
 158   explicit TupleBaseImpl(typename TupleTraits<Ts>::ParamType... args)
 159       : TupleLeaf<Ns, Ts>(args)... {}
 160 };
 161
 162 template <size_t N, typename T>
 163 struct TupleLeaf {
 164   TupleLeaf() {}
 165   explicit TupleLeaf(typename TupleTraits<T>::ParamType x) : x(x) {}
 166
 167   T& get() { return x; }
 168   const T& get() const { return x; }
 169
 170   T x;
 171 };
 172
 173 // Tuple getters --------------------------------------------------------------
 174 //
 175 // Allows accessing an arbitrary tuple element by index.
 176 //
 177 // Example usage:
 178 //   Tuple<int, double> t2;
 179 //   get<0>(t2) = 42;
 180 //   get<1>(t2) = 3.14;
 181
 182 template <size_t I, typename T>
 183 T& get(TupleLeaf<I, T>& leaf) {
 184   return leaf.get();
 185 }
 186
 187 template <size_t I, typename T>
 188 const T& get(const TupleLeaf<I, T>& leaf) {
 189   return leaf.get();
 190 }
 191
 192 // Tuple types ----------------------------------------------------------------
 193 //
 194 // Allows for selection of ValueTuple/RefTuple/ParamTuple without needing the
 195 // definitions of class types the tuple takes as parameters.
 196
 197 template <typename T>
 198 struct TupleTypes;
 199
 200 template <typename... Ts>
 201 struct TupleTypes<Tuple<Ts...>> {
 202   using ValueTuple = Tuple<typename TupleTraits<Ts>::ValueType...>;
 203   using RefTuple = Tuple<typename TupleTraits<Ts>::RefType...>;
 204   using ParamTuple = Tuple<typename TupleTraits<Ts>::ParamType...>;
 205 };
 206
 207 // Tuple creators -------------------------------------------------------------
 208 //
 209 // Helper functions for constructing tuples while inferring the template
 210 // argument types.
 211
 212 template <typename... Ts>
 213 inline Tuple<Ts...> MakeTuple(const Ts&... arg) {
 214   return Tuple<Ts...>(arg...);
 215 }
 216
 217 // The following set of helpers make what Boost refers to as "Tiers" - a tuple
 218 // of references.
 219
 220 template <typename... Ts>
 221 inline Tuple<Ts&...> MakeRefTuple(Ts&... arg) {
 222   return Tuple<Ts&...>(arg...);
 223 }
 224
 225 // Dispatchers ----------------------------------------------------------------
 226 //
 227 // Helper functions that call the given method on an object, with the unpacked
 228 // tuple arguments.  Notice that they all have the same number of arguments,
 229 // so you need only write:
 230 //   DispatchToMethod(object, &Object::method, args);
 231 // This is very useful for templated dispatchers, since they don't need to know
 232 // what type |args| is.
 233
 234 // Non-Static Dispatchers with no out params.
 235
 236 template <typename ObjT, typename Method, typename A>
 237 inline void DispatchToMethod(ObjT* obj, Method method, const A& arg) {
 238   (obj->*method)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 239 }
 240
 241 template <typename ObjT, typename Method, typename... Ts, size_t... Ns>
 242 inline void DispatchToMethodImpl(ObjT* obj,
 243                                  Method method,
 244                                  const Tuple<Ts...>& arg,
 245                                  IndexSequence<Ns...>) {
 246   (obj->*method)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 247 }
 248
 249 template <typename ObjT, typename Method, typename... Ts>
 250 inline void DispatchToMethod(ObjT* obj,
 251                              Method method,
 252                              const Tuple<Ts...>& arg) {
 253   DispatchToMethodImpl(obj, method, arg, MakeIndexSequence<sizeof...(Ts)>());
 254 }
 255
 256 // Static Dispatchers with no out params.
 257
 258 template <typename Function, typename A>
 259 inline void DispatchToMethod(Function function, const A& arg) {
 260   (*function)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 261 }
 262
 263 template <typename Function, typename... Ts, size_t... Ns>
 264 inline void DispatchToFunctionImpl(Function function,
 265                                    const Tuple<Ts...>& arg,
 266                                    IndexSequence<Ns...>) {
 267   (*function)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 268 }
 269
 270 template <typename Function, typename... Ts>
 271 inline void DispatchToFunction(Function function, const Tuple<Ts...>& arg) {
 272   DispatchToFunctionImpl(function, arg, MakeIndexSequence<sizeof...(Ts)>());
 273 }
 274
 275 // Dispatchers with out parameters.
 276
 277 template <typename ObjT,
 278           typename Method,
 279           typename In,
 280           typename... OutTs,
 281           size_t... OutNs>
 282 inline void DispatchToMethodImpl(ObjT* obj,
 283                                  Method method,
 284                                  const In& in,
 285                                  Tuple<OutTs...>* out,
 286                                  IndexSequence<OutNs...>) {
 287   (obj->*method)(base::internal::UnwrapTraits<In>::Unwrap(in),
 288                  &get<OutNs>(*out)...);
 289 }
 290
 291 template <typename ObjT, typename Method, typename In, typename... OutTs>
 292 inline void DispatchToMethod(ObjT* obj,
 293                              Method method,
 294                              const In& in,
 295                              Tuple<OutTs...>* out) {
 296   DispatchToMethodImpl(obj, method, in, out,
 297                        MakeIndexSequence<sizeof...(OutTs)>());
 298 }
 299
 300 template <typename ObjT,
 301           typename Method,
 302           typename... InTs,
 303           typename... OutTs,
 304           size_t... InNs,
 305           size_t... OutNs>
 306 inline void DispatchToMethodImpl(ObjT* obj,
 307                                  Method method,
 308                                  const Tuple<InTs...>& in,
 309                                  Tuple<OutTs...>* out,
 310                                  IndexSequence<InNs...>,
 311                                  IndexSequence<OutNs...>) {
 312   (obj->*method)(base::internal::UnwrapTraits<InTs>::Unwrap(get<InNs>(in))...,
 313                  &get<OutNs>(*out)...);
 314 }
 315
 316 template <typename ObjT, typename Method, typename... InTs, typename... OutTs>
 317 inline void DispatchToMethod(ObjT* obj,
 318                              Method method,
 319                              const Tuple<InTs...>& in,
 320                              Tuple<OutTs...>* out) {
 321   DispatchToMethodImpl(obj, method, in, out,
 322                        MakeIndexSequence<sizeof...(InTs)>(),
 323                        MakeIndexSequence<sizeof...(OutTs)>());
 324 }
 325
 326 #endif  // BASE_TUPLE_H__