1// { dg-options "-std=gnu++0x" } 2// { dg-do "run" } 3// A basic implementation of TR1's bind using variadic teplates 4// Contributed by Douglas Gregor <doug.gregor@gmail.com> 5#include <cassert> 6 7// Trivial reference_wrapper 8template<typename T> 9struct reference_wrapper 10{ 11 reference_wrapper(T& x) : ptr(&x) { } 12 13 operator T&() const { return *ptr; } 14 15 T& get() const { return *ptr; } 16 17 T* ptr; 18}; 19 20template<typename T> reference_wrapper<T> ref(T& x) { return x; } 21template<typename T> reference_wrapper<const T> cref(const T& x) { return x; } 22 23// Simple type-traits we'll need 24template<typename T> 25struct add_reference 26{ 27 typedef T& type; 28}; 29 30template<typename T> 31struct add_reference<T&> 32{ 33 typedef T& type; 34}; 35 36template<typename T, typename U> 37struct is_same 38{ 39 static const bool value = false; 40}; 41 42template<typename T> 43struct is_same<T, T> 44{ 45 static const bool value = true; 46}; 47 48// For creating the constructor parameters of tuple<> 49template<typename T> 50struct add_const_reference 51{ 52 typedef const T& type; 53}; 54 55template<typename T> 56struct add_const_reference<T&> 57{ 58 typedef T& type; 59}; 60 61// 6.1.3 Class template tuple: Needed for bind() implementation 62template<typename... Values> 63class tuple; 64 65template<> class tuple<> { }; 66 67template<typename Head, typename... Tail> 68class tuple<Head, Tail...> 69 : private tuple<Tail...> 70{ 71 typedef tuple<Tail...> inherited; 72 73 public: 74 tuple() { } 75 76 // implicit copy-constructor is okay 77 78 tuple(typename add_const_reference<Head>::type v, 79 typename add_const_reference<Tail>::type... vtail) 80 : m_head(v), inherited(vtail...) { } 81 82 template<typename... VValues> 83 tuple(const tuple<VValues...>& other) 84 : m_head(other.head()), inherited(other.tail()) { } 85 86 template<typename... VValues> 87 tuple& operator=(const tuple<VValues...>& other) 88 { 89 m_head = other.head(); 90 tail() = other.tail(); 91 return *this; 92 } 93 94 typename add_reference<Head>::type head() { return m_head; } 95 typename add_reference<const Head>::type head() const { return m_head; } 96 inherited& tail() { return *this; } 97 const inherited& tail() const { return *this; } 98 99 protected: 100 Head m_head; 101}; 102 103template<typename T> 104struct make_tuple_result 105{ 106 typedef T type; 107}; 108 109template<typename T> 110struct make_tuple_result<reference_wrapper<T> > 111{ 112 typedef T& type; 113}; 114 115// 6.1.3.2 Tuple creation functions 116struct ignore_t { 117 template<typename T> ignore_t& operator=(const T&) { return *this; } 118} ignore; 119 120template<typename... Values> 121tuple<typename make_tuple_result<Values>::type...> 122make_tuple(const Values&... values) 123{ 124 return tuple<typename make_tuple_result<Values>::type...>(values...); 125} 126 127template<typename... Values> 128tuple<Values&...> tie(Values&... values) 129{ 130 return tuple<Values&...>(values...); 131} 132 133// 6.1.3.3 Tuple helper classes 134template<typename Tuple> 135struct tuple_size; 136 137template<> 138struct tuple_size<tuple<> > 139{ 140 static const __SIZE_TYPE__ value = 0; 141}; 142 143template<typename Head, typename... Tail> 144struct tuple_size<tuple<Head, Tail...> > 145{ 146 static const __SIZE_TYPE__ value = 1 + tuple_size<tuple<Tail...> >::value; 147}; 148 149template<int I, typename Tuple> 150struct tuple_element; 151 152template<int I, typename Head, typename... Tail> 153struct tuple_element<I, tuple<Head, Tail...> > 154{ 155 typedef typename tuple_element<I-1, tuple<Tail...> >::type type; 156}; 157 158template<typename Head, typename... Tail> 159struct tuple_element<0, tuple<Head, Tail...> > 160{ 161 typedef Head type; 162}; 163 164// 6.1.3.4 Element access 165template<int I, typename Tuple> 166class get_impl; 167 168template<int I, typename Head, typename... Values> 169class get_impl<I, tuple<Head, Values...> > 170{ 171 typedef typename tuple_element<I-1, tuple<Values...> >::type Element; 172 typedef typename add_reference<Element>::type RJ; 173 typedef typename add_const_reference<Element>::type PJ; 174 typedef get_impl<I-1, tuple<Values...> > Next; 175 176 public: 177 static RJ get(tuple<Head, Values...>& t) 178 { return Next::get(t.tail()); } 179 180 static PJ get(const tuple<Head, Values...>& t) 181 { return Next::get(t.tail()); } 182}; 183 184template<typename Head, typename... Values> 185class get_impl<0, tuple<Head, Values...> > 186{ 187 typedef typename add_reference<Head>::type RJ; 188 typedef typename add_const_reference<Head>::type PJ; 189 190 public: 191 static RJ get(tuple<Head, Values...>& t) { return t.head(); } 192 static PJ get(const tuple<Head, Values...>& t) { return t.head(); } 193}; 194 195template<int I, typename... Values> 196typename add_reference< 197 typename tuple_element<I, tuple<Values...> >::type 198 >::type 199get(tuple<Values...>& t) 200{ 201 return get_impl<I, tuple<Values...> >::get(t); 202} 203 204template<int I, typename... Values> 205typename add_const_reference< 206 typename tuple_element<I, tuple<Values...> >::type 207 >::type 208get(const tuple<Values...>& t) 209{ 210 return get_impl<I, tuple<Values...> >::get(t); 211} 212 213// 6.1.3.5 Relational operators 214inline bool operator==(const tuple<>&, const tuple<>&) { return true; } 215 216template<typename T, typename... TTail, typename U, typename... UTail> 217bool operator==(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u) 218{ 219 return t.head() == u.head() && t.tail() == u.tail(); 220} 221 222template<typename... TValues, typename... UValues> 223bool operator!=(const tuple<TValues...>& t, const tuple<UValues...>& u) 224{ 225 return !(t == u); 226} 227 228inline bool operator<(const tuple<>&, const tuple<>&) { return false; } 229 230template<typename T, typename... TTail, typename U, typename... UTail> 231bool operator<(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u) 232{ 233 return (t.head() < u.head() || 234 (!(t.head() < u.head()) && t.tail() < u.tail())); 235} 236 237template<typename... TValues, typename... UValues> 238bool operator>(const tuple<TValues...>& t, const tuple<UValues...>& u) 239{ 240 return u < t; 241} 242 243template<typename... TValues, typename... UValues> 244bool operator<=(const tuple<TValues...>& t, const tuple<UValues...>& u) 245{ 246 return !(u < t); 247} 248 249template<typename... TValues, typename... UValues> 250bool operator>=(const tuple<TValues...>& t, const tuple<UValues...>& u) 251{ 252 return !(t < u); 253} 254 255// enable_if, the breakfast of champions 256template<bool Cond, typename Type = void> 257struct enable_if { 258 typedef Type type; 259}; 260 261template<typename Type> 262struct enable_if<false, Type> { }; 263 264// 3.6 Function object binders 265 266// 3.6.1 Class template is_bind_expression 267template<typename T> 268struct is_bind_expression { 269 static const bool value = false; 270}; 271 272// 3.6.2 Class template is_placeholder 273template<typename T> 274struct is_placeholder { 275 static const int value = 0; 276}; 277 278// 3.6.3 Function template bind 279template<int I> struct placeholder {} ; 280 281template<int N> struct int_c { }; 282 283// A tuple of integer values 284template<int...> struct int_tuple {}; 285 286// make_indexes_impl is a helper for make_indexes 287template<int I, typename IntTuple, typename... Types> 288struct make_indexes_impl; 289 290 291template<int I, int... Indexes, typename T, typename... Types> 292struct make_indexes_impl<I, int_tuple<Indexes...>, T, Types...> 293{ 294 typedef typename make_indexes_impl<I+1, 295 int_tuple<Indexes..., I>, 296 Types...>::type type; 297}; 298 299template<int I, int... Indexes> 300struct make_indexes_impl<I, int_tuple<Indexes...> > { 301 typedef int_tuple<Indexes...> type; 302}; 303 304// make_indexes takes a variable-length number of N types and 305// generates an int_tuple that contains <0, 1, 2, ..., N-1>. These can 306// be used as indexes for tuple's get or tuple_element operation. 307template<typename... Types> 308struct make_indexes : make_indexes_impl<0, int_tuple<>, Types...> { }; 309 310// Get the Ith tuple element, but only if I is in bounds. 311template<int I, typename Tuple, typename = void> 312struct safe_tuple_element{ }; 313 314template<int I, typename... Values> 315struct safe_tuple_element<I, tuple<Values...>, 316 typename enable_if<(I >= 0 && 317 I < tuple_size<tuple<Values...> >::value) 318 >::type> 319{ 320 typedef typename tuple_element<I, tuple<Values...> >::type type; 321}; 322 323// mu maps a bound argument to an actual argument, given a tuple of 324// the arguments passed to the function object returned by bind(). 325 326// Return the stored reference from reference_wrapper 327template<typename T, typename... Args> 328inline T& mu(reference_wrapper<T>& bound_arg, const tuple<Args&...>&) 329{ 330 return bound_arg.get(); 331} 332 333// Unwrap a tuple into separate arguments and forward to the function 334// object f. 335template<typename F, int... Indexes, typename... Args> 336inline typename F::result_type 337unwrap_and_forward(F& f, int_tuple<Indexes...>, const tuple<Args&...>& args) 338{ 339 return f(get<Indexes>(args)...); 340} 341 342// Evaluate the inner bind expression 343template<typename Bound, typename... Args> 344inline typename enable_if<is_bind_expression<Bound>::value, 345 typename Bound::result_type>::type 346mu(Bound& bound_arg, const tuple<Args&...>& args) 347{ 348 typedef typename make_indexes<Args...>::type Indexes; 349 return unwrap_and_forward(bound_arg, Indexes(), args); 350} 351 352// Retrieve the Ith argument from args 353template<typename Bound, typename... Args> 354inline typename safe_tuple_element<is_placeholder<Bound>::value - 1, 355 tuple<Args...> >::type 356mu(Bound& bound_arg, const tuple<Args&...>& args) 357{ 358 return get<is_placeholder<Bound>::value-1>(args); 359} 360 361// Return the stored value. 362template<typename T> 363struct is_reference_wrapper { 364 static const bool value = false; 365}; 366 367template<typename T> 368struct is_reference_wrapper<reference_wrapper<T> > { 369 static const bool value = true; 370}; 371 372template<typename Bound, typename... Args> 373inline typename enable_if<(!is_bind_expression<Bound>::value 374 && !is_placeholder<Bound>::value 375 && !is_reference_wrapper<Bound>::value), 376 Bound&>::type 377mu(Bound& bound_arg, const tuple<Args&...>&) 378{ 379 return bound_arg; 380} 381 382// 383template<typename F, typename... BoundArgs, int... Indexes, typename... Args> 384typename F::result_type 385apply_functor(F& f, tuple<BoundArgs...>& bound_args, int_tuple<Indexes...>, 386 const tuple<Args&...>& args) 387{ 388 return f(mu(get<Indexes>(bound_args), args)...); 389} 390 391template<typename F, typename... BoundArgs> 392class bound_functor 393{ 394 typedef typename make_indexes<BoundArgs...>::type indexes; 395 396 public: 397 typedef typename F::result_type result_type; 398 399 explicit bound_functor(const F& f, const BoundArgs&... bound_args) 400 : f(f), bound_args(bound_args...) { } 401 402 template<typename... Args> 403 typename F::result_type operator()(Args&... args) { 404 return apply_functor(f, bound_args, indexes(), tie(args...)); 405 } 406 407 private: 408 F f; 409 tuple<BoundArgs...> bound_args; 410}; 411 412template<typename F, typename... BoundArgs> 413struct is_bind_expression<bound_functor<F, BoundArgs...> > { 414 static const bool value = true; 415}; 416 417template<typename F, typename... BoundArgs> 418inline bound_functor<F, BoundArgs...> 419bind(const F& f, const BoundArgs&... bound_args) 420{ 421 return bound_functor<F, BoundArgs...>(f, bound_args...); 422} 423 424 425// 3.6.4 Placeholders 426template<int I> 427struct is_placeholder<placeholder<I> > { 428 static const int value = I; 429}; 430 431placeholder<1> _1; 432placeholder<2> _2; 433placeholder<3> _3; 434placeholder<4> _4; 435placeholder<5> _5; 436placeholder<6> _6; 437placeholder<7> _7; 438placeholder<8> _8; 439placeholder<9> _9; 440 441// Test code 442template<typename T> 443struct plus { 444 typedef T result_type; 445 446 T operator()(T x, T y) { return x + y; } 447}; 448 449template<typename T> 450struct multiplies { 451 typedef T result_type; 452 453 T operator()(T x, T y) { return x * y; } 454}; 455 456template<typename T> 457struct negate { 458 typedef T result_type; 459 460 T operator()(T x) { return -x; } 461}; 462 463int main() 464{ 465 int seventeen = 17; 466 int forty_two = 42; 467 468 assert(bind(plus<int>(), _1, _2)(seventeen, forty_two) == 59); 469 assert(bind(plus<int>(), _1, _1)(seventeen, forty_two) == 34); 470 assert(bind(plus<int>(), _2, _1)(seventeen, forty_two) == 59); 471 assert(bind(plus<int>(), 5, _1)(seventeen, forty_two) == 22); 472 assert(bind(plus<int>(), ref(seventeen), _2)(seventeen, forty_two) == 59); 473 assert(bind(plus<int>(), bind(multiplies<int>(), 3, _1), _2)(seventeen, forty_two) 474 == 93); 475 return 0; 476} 477