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 template <> struct MakeIndexSequenceImpl<12> {
  85   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10,11>;
  86 };
  87 template <> struct MakeIndexSequenceImpl<13> {
  88   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10,11,12>;
  89 };
  90
  91 #else  // defined(WIN) && defined(_PREFAST_)
  92
  93 template <size_t... Ns>
  94 struct MakeIndexSequenceImpl<0, Ns...> {
  95   using Type = IndexSequence<Ns...>;
  96 };
  97
  98 template <size_t N, size_t... Ns>
  99 struct MakeIndexSequenceImpl<N, Ns...>
 100     : MakeIndexSequenceImpl<N - 1, N - 1, Ns...> {};
 101
 102 #endif  // defined(WIN) && defined(_PREFAST_)
 103
 104 template <size_t N>
 105 using MakeIndexSequence = typename MakeIndexSequenceImpl<N>::Type;
 106
 107 // Traits ----------------------------------------------------------------------
 108 //
 109 // A simple traits class for tuple arguments.
 110 //
 111 // ValueType: the bare, nonref version of a type (same as the type for nonrefs).
 112 // RefType: the ref version of a type (same as the type for refs).
 113 // ParamType: what type to pass to functions (refs should not be constified).
 114
 115 template <class P>
 116 struct TupleTraits {
 117   typedef P ValueType;
 118   typedef P& RefType;
 119   typedef const P& ParamType;
 120 };
 121
 122 template <class P>
 123 struct TupleTraits<P&> {
 124   typedef P ValueType;
 125   typedef P& RefType;
 126   typedef P& ParamType;
 127 };
 128
 129 // Tuple -----------------------------------------------------------------------
 130 //
 131 // This set of classes is useful for bundling 0 or more heterogeneous data types
 132 // into a single variable.  The advantage of this is that it greatly simplifies
 133 // function objects that need to take an arbitrary number of parameters; see
 134 // RunnableMethod and IPC::MessageWithTuple.
 135 //
 136 // Tuple<> is supplied to act as a 'void' type.  It can be used, for example,
 137 // when dispatching to a function that accepts no arguments (see the
 138 // Dispatchers below).
 139 // Tuple<A> is rarely useful.  One such use is when A is non-const ref that you
 140 // want filled by the dispatchee, and the tuple is merely a container for that
 141 // output (a "tier").  See MakeRefTuple and its usages.
 142
 143 template <typename IxSeq, typename... Ts>
 144 struct TupleBaseImpl;
 145 template <typename... Ts>
 146 using TupleBase = TupleBaseImpl<MakeIndexSequence<sizeof...(Ts)>, Ts...>;
 147 template <size_t N, typename T>
 148 struct TupleLeaf;
 149
 150 template <typename... Ts>
 151 struct Tuple : TupleBase<Ts...> {
 152   Tuple() : TupleBase<Ts...>() {}
 153   explicit Tuple(typename TupleTraits<Ts>::ParamType... args)
 154       : TupleBase<Ts...>(args...) {}
 155 };
 156
 157 // Avoids ambiguity between Tuple's two constructors.
 158 template <>
 159 struct Tuple<> {};
 160
 161 template <size_t... Ns, typename... Ts>
 162 struct TupleBaseImpl<IndexSequence<Ns...>, Ts...> : TupleLeaf<Ns, Ts>... {
 163   TupleBaseImpl() : TupleLeaf<Ns, Ts>()... {}
 164   explicit TupleBaseImpl(typename TupleTraits<Ts>::ParamType... args)
 165       : TupleLeaf<Ns, Ts>(args)... {}
 166 };
 167
 168 template <size_t N, typename T>
 169 struct TupleLeaf {
 170   TupleLeaf() {}
 171   explicit TupleLeaf(typename TupleTraits<T>::ParamType x) : x(x) {}
 172
 173   T& get() { return x; }
 174   const T& get() const { return x; }
 175
 176   T x;
 177 };
 178
 179 // Tuple getters --------------------------------------------------------------
 180 //
 181 // Allows accessing an arbitrary tuple element by index.
 182 //
 183 // Example usage:
 184 //   Tuple<int, double> t2;
 185 //   get<0>(t2) = 42;
 186 //   get<1>(t2) = 3.14;
 187
 188 template <size_t I, typename T>
 189 T& get(TupleLeaf<I, T>& leaf) {
 190   return leaf.get();
 191 }
 192
 193 template <size_t I, typename T>
 194 const T& get(const TupleLeaf<I, T>& leaf) {
 195   return leaf.get();
 196 }
 197
 198 // Tuple types ----------------------------------------------------------------
 199 //
 200 // Allows for selection of ValueTuple/RefTuple/ParamTuple without needing the
 201 // definitions of class types the tuple takes as parameters.
 202
 203 template <typename T>
 204 struct TupleTypes;
 205
 206 template <typename... Ts>
 207 struct TupleTypes<Tuple<Ts...>> {
 208   using ValueTuple = Tuple<typename TupleTraits<Ts>::ValueType...>;
 209   using RefTuple = Tuple<typename TupleTraits<Ts>::RefType...>;
 210   using ParamTuple = Tuple<typename TupleTraits<Ts>::ParamType...>;
 211 };
 212
 213 // Tuple creators -------------------------------------------------------------
 214 //
 215 // Helper functions for constructing tuples while inferring the template
 216 // argument types.
 217
 218 template <typename... Ts>
 219 inline Tuple<Ts...> MakeTuple(const Ts&... arg) {
 220   return Tuple<Ts...>(arg...);
 221 }
 222
 223 // The following set of helpers make what Boost refers to as "Tiers" - a tuple
 224 // of references.
 225
 226 template <typename... Ts>
 227 inline Tuple<Ts&...> MakeRefTuple(Ts&... arg) {
 228   return Tuple<Ts&...>(arg...);
 229 }
 230
 231 // Dispatchers ----------------------------------------------------------------
 232 //
 233 // Helper functions that call the given method on an object, with the unpacked
 234 // tuple arguments.  Notice that they all have the same number of arguments,
 235 // so you need only write:
 236 //   DispatchToMethod(object, &Object::method, args);
 237 // This is very useful for templated dispatchers, since they don't need to know
 238 // what type |args| is.
 239
 240 // Non-Static Dispatchers with no out params.
 241
 242 template <typename ObjT, typename Method, typename A>
 243 inline void DispatchToMethod(ObjT* obj, Method method, const A& arg) {
 244   (obj->*method)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 245 }
 246
 247 template <typename ObjT, typename Method, typename... Ts, size_t... Ns>
 248 inline void DispatchToMethodImpl(ObjT* obj,
 249                                  Method method,
 250                                  const Tuple<Ts...>& arg,
 251                                  IndexSequence<Ns...>) {
 252   (obj->*method)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 253 }
 254
 255 template <typename ObjT, typename Method, typename... Ts>
 256 inline void DispatchToMethod(ObjT* obj,
 257                              Method method,
 258                              const Tuple<Ts...>& arg) {
 259   DispatchToMethodImpl(obj, method, arg, MakeIndexSequence<sizeof...(Ts)>());
 260 }
 261
 262 // Static Dispatchers with no out params.
 263
 264 template <typename Function, typename A>
 265 inline void DispatchToMethod(Function function, const A& arg) {
 266   (*function)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 267 }
 268
 269 template <typename Function, typename... Ts, size_t... Ns>
 270 inline void DispatchToFunctionImpl(Function function,
 271                                    const Tuple<Ts...>& arg,
 272                                    IndexSequence<Ns...>) {
 273   (*function)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 274 }
 275
 276 template <typename Function, typename... Ts>
 277 inline void DispatchToFunction(Function function, const Tuple<Ts...>& arg) {
 278   DispatchToFunctionImpl(function, arg, MakeIndexSequence<sizeof...(Ts)>());
 279 }
 280
 281 // Dispatchers with out parameters.
 282
 283 template <typename ObjT,
 284           typename Method,
 285           typename In,
 286           typename... OutTs,
 287           size_t... OutNs>
 288 inline void DispatchToMethodImpl(ObjT* obj,
 289                                  Method method,
 290                                  const In& in,
 291                                  Tuple<OutTs...>* out,
 292                                  IndexSequence<OutNs...>) {
 293   (obj->*method)(base::internal::UnwrapTraits<In>::Unwrap(in),
 294                  &get<OutNs>(*out)...);
 295 }
 296
 297 template <typename ObjT, typename Method, typename In, typename... OutTs>
 298 inline void DispatchToMethod(ObjT* obj,
 299                              Method method,
 300                              const In& in,
 301                              Tuple<OutTs...>* out) {
 302   DispatchToMethodImpl(obj, method, in, out,
 303                        MakeIndexSequence<sizeof...(OutTs)>());
 304 }
 305
 306 template <typename ObjT,
 307           typename Method,
 308           typename... InTs,
 309           typename... OutTs,
 310           size_t... InNs,
 311           size_t... OutNs>
 312 inline void DispatchToMethodImpl(ObjT* obj,
 313                                  Method method,
 314                                  const Tuple<InTs...>& in,
 315                                  Tuple<OutTs...>* out,
 316                                  IndexSequence<InNs...>,
 317                                  IndexSequence<OutNs...>) {
 318   (obj->*method)(base::internal::UnwrapTraits<InTs>::Unwrap(get<InNs>(in))...,
 319                  &get<OutNs>(*out)...);
 320 }
 321
 322 template <typename ObjT, typename Method, typename... InTs, typename... OutTs>
 323 inline void DispatchToMethod(ObjT* obj,
 324                              Method method,
 325                              const Tuple<InTs...>& in,
 326                              Tuple<OutTs...>* out) {
 327   DispatchToMethodImpl(obj, method, in, out,
 328                        MakeIndexSequence<sizeof...(InTs)>(),
 329                        MakeIndexSequence<sizeof...(OutTs)>());
 330 }
 331
 332 #endif  // BASE_TUPLE_H_