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 namespace base {
  34
  35 // Index sequences
  36 //
  37 // Minimal clone of the similarly-named C++14 functionality.
  38
  39 template <size_t...>
  40 struct IndexSequence {};
  41
  42 template <size_t... Ns>
  43 struct MakeIndexSequenceImpl;
  44
  45 #if defined(_PREFAST_) && defined(OS_WIN)
  46
  47 // Work around VC++ 2013 /analyze internal compiler error:
  48 // https://connect.microsoft.com/VisualStudio/feedback/details/1053626
  49
  50 template <> struct MakeIndexSequenceImpl<0> {
  51   using Type = IndexSequence<>;
  52 };
  53 template <> struct MakeIndexSequenceImpl<1> {
  54   using Type = IndexSequence<0>;
  55 };
  56 template <> struct MakeIndexSequenceImpl<2> {
  57   using Type = IndexSequence<0,1>;
  58 };
  59 template <> struct MakeIndexSequenceImpl<3> {
  60   using Type = IndexSequence<0,1,2>;
  61 };
  62 template <> struct MakeIndexSequenceImpl<4> {
  63   using Type = IndexSequence<0,1,2,3>;
  64 };
  65 template <> struct MakeIndexSequenceImpl<5> {
  66   using Type = IndexSequence<0,1,2,3,4>;
  67 };
  68 template <> struct MakeIndexSequenceImpl<6> {
  69   using Type = IndexSequence<0,1,2,3,4,5>;
  70 };
  71 template <> struct MakeIndexSequenceImpl<7> {
  72   using Type = IndexSequence<0,1,2,3,4,5,6>;
  73 };
  74 template <> struct MakeIndexSequenceImpl<8> {
  75   using Type = IndexSequence<0,1,2,3,4,5,6,7>;
  76 };
  77 template <> struct MakeIndexSequenceImpl<9> {
  78   using Type = IndexSequence<0,1,2,3,4,5,6,7,8>;
  79 };
  80 template <> struct MakeIndexSequenceImpl<10> {
  81   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9>;
  82 };
  83 template <> struct MakeIndexSequenceImpl<11> {
  84   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10>;
  85 };
  86 template <> struct MakeIndexSequenceImpl<12> {
  87   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10,11>;
  88 };
  89 template <> struct MakeIndexSequenceImpl<13> {
  90   using Type = IndexSequence<0,1,2,3,4,5,6,7,8,9,10,11,12>;
  91 };
  92
  93 #else  // defined(WIN) && defined(_PREFAST_)
  94
  95 template <size_t... Ns>
  96 struct MakeIndexSequenceImpl<0, Ns...> {
  97   using Type = IndexSequence<Ns...>;
  98 };
  99
 100 template <size_t N, size_t... Ns>
 101 struct MakeIndexSequenceImpl<N, Ns...>
 102     : MakeIndexSequenceImpl<N - 1, N - 1, Ns...> {};
 103
 104 #endif  // defined(WIN) && defined(_PREFAST_)
 105
 106 template <size_t N>
 107 using MakeIndexSequence = typename MakeIndexSequenceImpl<N>::Type;
 108
 109 // Traits ----------------------------------------------------------------------
 110 //
 111 // A simple traits class for tuple arguments.
 112 //
 113 // ValueType: the bare, nonref version of a type (same as the type for nonrefs).
 114 // RefType: the ref version of a type (same as the type for refs).
 115 // ParamType: what type to pass to functions (refs should not be constified).
 116
 117 template <class P>
 118 struct TupleTraits {
 119   typedef P ValueType;
 120   typedef P& RefType;
 121   typedef const P& ParamType;
 122 };
 123
 124 template <class P>
 125 struct TupleTraits<P&> {
 126   typedef P ValueType;
 127   typedef P& RefType;
 128   typedef P& ParamType;
 129 };
 130
 131 // Tuple -----------------------------------------------------------------------
 132 //
 133 // This set of classes is useful for bundling 0 or more heterogeneous data types
 134 // into a single variable.  The advantage of this is that it greatly simplifies
 135 // function objects that need to take an arbitrary number of parameters; see
 136 // RunnableMethod and IPC::MessageWithTuple.
 137 //
 138 // Tuple<> is supplied to act as a 'void' type.  It can be used, for example,
 139 // when dispatching to a function that accepts no arguments (see the
 140 // Dispatchers below).
 141 // Tuple<A> is rarely useful.  One such use is when A is non-const ref that you
 142 // want filled by the dispatchee, and the tuple is merely a container for that
 143 // output (a "tier").  See MakeRefTuple and its usages.
 144
 145 template <typename IxSeq, typename... Ts>
 146 struct TupleBaseImpl;
 147 template <typename... Ts>
 148 using TupleBase = TupleBaseImpl<MakeIndexSequence<sizeof...(Ts)>, Ts...>;
 149 template <size_t N, typename T>
 150 struct TupleLeaf;
 151
 152 template <typename... Ts>
 153 struct Tuple : TupleBase<Ts...> {
 154   Tuple() : TupleBase<Ts...>() {}
 155   explicit Tuple(typename TupleTraits<Ts>::ParamType... args)
 156       : TupleBase<Ts...>(args...) {}
 157 };
 158
 159 // Avoids ambiguity between Tuple's two constructors.
 160 template <>
 161 struct Tuple<> {};
 162
 163 template <size_t... Ns, typename... Ts>
 164 struct TupleBaseImpl<IndexSequence<Ns...>, Ts...> : TupleLeaf<Ns, Ts>... {
 165   TupleBaseImpl() : TupleLeaf<Ns, Ts>()... {}
 166   explicit TupleBaseImpl(typename TupleTraits<Ts>::ParamType... args)
 167       : TupleLeaf<Ns, Ts>(args)... {}
 168 };
 169
 170 template <size_t N, typename T>
 171 struct TupleLeaf {
 172   TupleLeaf() {}
 173   explicit TupleLeaf(typename TupleTraits<T>::ParamType x) : x(x) {}
 174
 175   T& get() { return x; }
 176   const T& get() const { return x; }
 177
 178   T x;
 179 };
 180
 181 // Tuple getters --------------------------------------------------------------
 182 //
 183 // Allows accessing an arbitrary tuple element by index.
 184 //
 185 // Example usage:
 186 //   base::Tuple<int, double> t2;
 187 //   base::get<0>(t2) = 42;
 188 //   base::get<1>(t2) = 3.14;
 189
 190 template <size_t I, typename T>
 191 T& get(TupleLeaf<I, T>& leaf) {
 192   return leaf.get();
 193 }
 194
 195 template <size_t I, typename T>
 196 const T& get(const TupleLeaf<I, T>& leaf) {
 197   return leaf.get();
 198 }
 199
 200 // Tuple types ----------------------------------------------------------------
 201 //
 202 // Allows for selection of ValueTuple/RefTuple/ParamTuple without needing the
 203 // definitions of class types the tuple takes as parameters.
 204
 205 template <typename T>
 206 struct TupleTypes;
 207
 208 template <typename... Ts>
 209 struct TupleTypes<Tuple<Ts...>> {
 210   using ValueTuple = Tuple<typename TupleTraits<Ts>::ValueType...>;
 211   using RefTuple = Tuple<typename TupleTraits<Ts>::RefType...>;
 212   using ParamTuple = Tuple<typename TupleTraits<Ts>::ParamType...>;
 213 };
 214
 215 // Tuple creators -------------------------------------------------------------
 216 //
 217 // Helper functions for constructing tuples while inferring the template
 218 // argument types.
 219
 220 template <typename... Ts>
 221 inline Tuple<Ts...> MakeTuple(const Ts&... arg) {
 222   return Tuple<Ts...>(arg...);
 223 }
 224
 225 // The following set of helpers make what Boost refers to as "Tiers" - a tuple
 226 // of references.
 227
 228 template <typename... Ts>
 229 inline Tuple<Ts&...> MakeRefTuple(Ts&... arg) {
 230   return Tuple<Ts&...>(arg...);
 231 }
 232
 233 // Dispatchers ----------------------------------------------------------------
 234 //
 235 // Helper functions that call the given method on an object, with the unpacked
 236 // tuple arguments.  Notice that they all have the same number of arguments,
 237 // so you need only write:
 238 //   DispatchToMethod(object, &Object::method, args);
 239 // This is very useful for templated dispatchers, since they don't need to know
 240 // what type |args| is.
 241
 242 // Non-Static Dispatchers with no out params.
 243
 244 template <typename ObjT, typename Method, typename A>
 245 inline void DispatchToMethod(ObjT* obj, Method method, const A& arg) {
 246   (obj->*method)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 247 }
 248
 249 template <typename ObjT, typename Method, typename... Ts, size_t... Ns>
 250 inline void DispatchToMethodImpl(ObjT* obj,
 251                                  Method method,
 252                                  const Tuple<Ts...>& arg,
 253                                  IndexSequence<Ns...>) {
 254   (obj->*method)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 255 }
 256
 257 template <typename ObjT, typename Method, typename... Ts>
 258 inline void DispatchToMethod(ObjT* obj,
 259                              Method method,
 260                              const Tuple<Ts...>& arg) {
 261   DispatchToMethodImpl(obj, method, arg, MakeIndexSequence<sizeof...(Ts)>());
 262 }
 263
 264 // Static Dispatchers with no out params.
 265
 266 template <typename Function, typename A>
 267 inline void DispatchToMethod(Function function, const A& arg) {
 268   (*function)(base::internal::UnwrapTraits<A>::Unwrap(arg));
 269 }
 270
 271 template <typename Function, typename... Ts, size_t... Ns>
 272 inline void DispatchToFunctionImpl(Function function,
 273                                    const Tuple<Ts...>& arg,
 274                                    IndexSequence<Ns...>) {
 275   (*function)(base::internal::UnwrapTraits<Ts>::Unwrap(get<Ns>(arg))...);
 276 }
 277
 278 template <typename Function, typename... Ts>
 279 inline void DispatchToFunction(Function function, const Tuple<Ts...>& arg) {
 280   DispatchToFunctionImpl(function, arg, MakeIndexSequence<sizeof...(Ts)>());
 281 }
 282
 283 // Dispatchers with out parameters.
 284
 285 template <typename ObjT,
 286           typename Method,
 287           typename In,
 288           typename... OutTs,
 289           size_t... OutNs>
 290 inline void DispatchToMethodImpl(ObjT* obj,
 291                                  Method method,
 292                                  const In& in,
 293                                  Tuple<OutTs...>* out,
 294                                  IndexSequence<OutNs...>) {
 295   (obj->*method)(base::internal::UnwrapTraits<In>::Unwrap(in),
 296                  &get<OutNs>(*out)...);
 297 }
 298
 299 template <typename ObjT, typename Method, typename In, typename... OutTs>
 300 inline void DispatchToMethod(ObjT* obj,
 301                              Method method,
 302                              const In& in,
 303                              Tuple<OutTs...>* out) {
 304   DispatchToMethodImpl(obj, method, in, out,
 305                        MakeIndexSequence<sizeof...(OutTs)>());
 306 }
 307
 308 template <typename ObjT,
 309           typename Method,
 310           typename... InTs,
 311           typename... OutTs,
 312           size_t... InNs,
 313           size_t... OutNs>
 314 inline void DispatchToMethodImpl(ObjT* obj,
 315                                  Method method,
 316                                  const Tuple<InTs...>& in,
 317                                  Tuple<OutTs...>* out,
 318                                  IndexSequence<InNs...>,
 319                                  IndexSequence<OutNs...>) {
 320   (obj->*method)(base::internal::UnwrapTraits<InTs>::Unwrap(get<InNs>(in))...,
 321                  &get<OutNs>(*out)...);
 322 }
 323
 324 template <typename ObjT, typename Method, typename... InTs, typename... OutTs>
 325 inline void DispatchToMethod(ObjT* obj,
 326                              Method method,
 327                              const Tuple<InTs...>& in,
 328                              Tuple<OutTs...>* out) {
 329   DispatchToMethodImpl(obj, method, in, out,
 330                        MakeIndexSequence<sizeof...(InTs)>(),
 331                        MakeIndexSequence<sizeof...(OutTs)>());
 332 }
 333
 334 }  // namespace base
 335
 336 #endif  // BASE_TUPLE_H_