1 // { dg-do run { target c++11 } }
2 // A basic implementation of TR1's bind using variadic teplates
3 // Contributed by Douglas Gregor <doug.gregor@gmail.com>
4 #include <cassert>
5 
6 // Trivial reference_wrapper
7 template<typename T>
8 struct reference_wrapper
9 {
reference_wrapperreference_wrapper10   reference_wrapper(T& x) : ptr(&x) { }
11 
12   operator T&() const { return *ptr; }
13 
getreference_wrapper14   T& get() const { return *ptr; }
15 
16   T* ptr;
17 };
18 
ref(T & x)19 template<typename T> reference_wrapper<T> ref(T& x) { return x; }
cref(const T & x)20 template<typename T> reference_wrapper<const T> cref(const T& x) { return x; }
21 
22 // Simple type-traits we'll need
23 template<typename T>
24 struct add_reference
25 {
26   typedef T& type;
27 };
28 
29 template<typename T>
30 struct add_reference<T&>
31 {
32   typedef T& type;
33 };
34 
35 template<typename T, typename U>
36 struct is_same
37 {
38   static const bool value = false;
39 };
40 
41 template<typename T>
42 struct is_same<T, T>
43 {
44   static const bool value = true;
45 };
46 
47 // For creating the constructor parameters of tuple<>
48 template<typename T>
49 struct add_const_reference
50 {
51   typedef const T& type;
52 };
53 
54 template<typename T>
55 struct add_const_reference<T&>
56 {
57   typedef T& type;
58 };
59 
60 // 6.1.3 Class template tuple: Needed for bind() implementation
61 template<typename... Values>
62 class tuple;
63 
64 template<> class tuple<> { };
65 
66 template<typename Head, typename... Tail>
67 class tuple<Head, Tail...>
68   : private tuple<Tail...>
69 {
70   typedef tuple<Tail...> inherited;
71 
72  public:
73   tuple() { }
74 
75   // implicit copy-constructor is okay
76 
77   tuple(typename add_const_reference<Head>::type v,
78         typename add_const_reference<Tail>::type... vtail)
79     : m_head(v), inherited(vtail...) { }
80 
81   template<typename... VValues>
82   tuple(const tuple<VValues...>& other)
83     : m_head(other.head()), inherited(other.tail()) { }
84 
85   template<typename... VValues>
86   tuple& operator=(const tuple<VValues...>& other)
87   {
88     m_head = other.head();
89     tail() = other.tail();
90     return *this;
91   }
92 
93   typename add_reference<Head>::type       head()       { return m_head; }
94   typename add_reference<const Head>::type head() const { return m_head; }
95   inherited&                               tail()       { return *this; }
96   const inherited&                         tail() const { return *this; }
97 
98  protected:
99   Head m_head;
100 };
101 
102 template<typename T>
103 struct make_tuple_result
104 {
105   typedef T type;
106 };
107 
108 template<typename T>
109 struct make_tuple_result<reference_wrapper<T> >
110 {
111   typedef T& type;
112 };
113 
114 // 6.1.3.2 Tuple creation functions
115 struct ignore_t {
116   template<typename T> ignore_t& operator=(const T&) { return *this; }
117 } ignore;
118 
119 template<typename... Values>
120 tuple<typename make_tuple_result<Values>::type...>
121 make_tuple(const Values&... values)
122 {
123   return tuple<typename make_tuple_result<Values>::type...>(values...);
124 }
125 
126 template<typename... Values>
127 tuple<Values&...> tie(Values&... values)
128 {
129   return tuple<Values&...>(values...);
130 }
131 
132 // 6.1.3.3 Tuple helper classes
133 template<typename Tuple>
134 struct tuple_size;
135 
136 template<>
137 struct tuple_size<tuple<> >
138 {
139   static const __SIZE_TYPE__ value = 0;
140 };
141 
142 template<typename Head, typename... Tail>
143 struct tuple_size<tuple<Head, Tail...> >
144 {
145   static const __SIZE_TYPE__ value = 1 + tuple_size<tuple<Tail...> >::value;
146 };
147 
148 template<int I, typename Tuple>
149 struct tuple_element;
150 
151 template<int I, typename Head, typename... Tail>
152 struct tuple_element<I, tuple<Head, Tail...> >
153 {
154   typedef typename tuple_element<I-1, tuple<Tail...> >::type type;
155 };
156 
157 template<typename Head, typename... Tail>
158 struct tuple_element<0, tuple<Head, Tail...> >
159 {
160   typedef Head type;
161 };
162 
163 // 6.1.3.4 Element access
164 template<int I, typename Tuple>
165 class get_impl;
166 
167 template<int I, typename Head, typename... Values>
168 class get_impl<I, tuple<Head, Values...> >
169 {
170   typedef typename tuple_element<I-1, tuple<Values...> >::type Element;
171   typedef typename add_reference<Element>::type RJ;
172   typedef typename add_const_reference<Element>::type PJ;
173   typedef get_impl<I-1, tuple<Values...> > Next;
174 
175  public:
176   static RJ get(tuple<Head, Values...>& t)
177   { return Next::get(t.tail()); }
178 
179   static PJ get(const tuple<Head, Values...>& t)
180   { return Next::get(t.tail()); }
181 };
182 
183 template<typename Head, typename... Values>
184 class get_impl<0, tuple<Head, Values...> >
185 {
186   typedef typename add_reference<Head>::type RJ;
187   typedef typename add_const_reference<Head>::type PJ;
188 
189  public:
190   static RJ get(tuple<Head, Values...>& t)       { return t.head(); }
191   static PJ get(const tuple<Head, Values...>& t) { return t.head(); }
192 };
193 
194 template<int I, typename... Values>
195 typename add_reference<
196            typename tuple_element<I, tuple<Values...> >::type
197          >::type
198 get(tuple<Values...>& t)
199 {
200   return get_impl<I, tuple<Values...> >::get(t);
201 }
202 
203 template<int I, typename... Values>
204 typename add_const_reference<
205            typename tuple_element<I, tuple<Values...> >::type
206          >::type
207 get(const tuple<Values...>& t)
208 {
209   return get_impl<I, tuple<Values...> >::get(t);
210 }
211 
212 // 6.1.3.5 Relational operators
213 inline bool operator==(const tuple<>&, const tuple<>&) { return true; }
214 
215 template<typename T, typename... TTail, typename U, typename... UTail>
216 bool operator==(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u)
217 {
218   return t.head() == u.head() && t.tail() == u.tail();
219 }
220 
221 template<typename... TValues, typename... UValues>
222 bool operator!=(const tuple<TValues...>& t, const tuple<UValues...>& u)
223 {
224   return !(t == u);
225 }
226 
227 inline bool operator<(const tuple<>&, const tuple<>&) { return false; }
228 
229 template<typename T, typename... TTail, typename U, typename... UTail>
230 bool operator<(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u)
231 {
232   return (t.head() < u.head() ||
233           (!(t.head() < u.head()) && t.tail() < u.tail()));
234 }
235 
236 template<typename... TValues, typename... UValues>
237 bool operator>(const tuple<TValues...>& t, const tuple<UValues...>& u)
238 {
239   return u < t;
240 }
241 
242 template<typename... TValues, typename... UValues>
243 bool operator<=(const tuple<TValues...>& t, const tuple<UValues...>& u)
244 {
245   return !(u < t);
246 }
247 
248 template<typename... TValues, typename... UValues>
249 bool operator>=(const tuple<TValues...>& t, const tuple<UValues...>& u)
250 {
251   return !(t < u);
252 }
253 
254 // enable_if, the breakfast of champions
255 template<bool Cond, typename Type = void>
256 struct enable_if {
257   typedef Type type;
258 };
259 
260 template<typename Type>
261 struct enable_if<false, Type> { };
262 
263 // 3.6 Function object binders
264 
265 // 3.6.1 Class template is_bind_expression
266 template<typename T>
267 struct is_bind_expression {
268   static const bool value = false;
269 };
270 
271 // 3.6.2 Class template is_placeholder
272 template<typename T>
273 struct is_placeholder {
274   static const int value = 0;
275 };
276 
277 // 3.6.3 Function template bind
278 template<int I> struct placeholder {} ;
279 
280 template<int N> struct int_c { };
281 
282 // A tuple of integer values
283 template<int...> struct int_tuple {};
284 
285 // make_indexes_impl is a helper for make_indexes
286 template<int I, typename IntTuple, typename... Types>
287 struct make_indexes_impl;
288 
289 
290 template<int I, int... Indexes, typename T, typename... Types>
291 struct make_indexes_impl<I, int_tuple<Indexes...>, T, Types...>
292 {
293   typedef typename make_indexes_impl<I+1,
294                                      int_tuple<Indexes..., I>,
295                                      Types...>::type type;
296 };
297 
298 template<int I, int... Indexes>
299 struct make_indexes_impl<I, int_tuple<Indexes...> > {
300   typedef int_tuple<Indexes...> type;
301 };
302 
303 // make_indexes takes a variable-length number of N types and
304 // generates an int_tuple that contains <0, 1, 2, ..., N-1>. These can
305 // be used as indexes for tuple's get or tuple_element operation.
306 template<typename... Types>
307 struct make_indexes : make_indexes_impl<0, int_tuple<>, Types...> { };
308 
309 // Get the Ith tuple element, but only if I is in bounds.
310 template<int I, typename Tuple, typename = void>
311 struct safe_tuple_element{ };
312 
313 template<int I, typename... Values>
314 struct safe_tuple_element<I, tuple<Values...>,
315          typename enable_if<(I >= 0 &&
316                              I < tuple_size<tuple<Values...> >::value)
317                             >::type>
318 {
319   typedef typename tuple_element<I, tuple<Values...> >::type type;
320 };
321 
322 // mu maps a bound argument to an actual argument, given a tuple of
323 // the arguments passed to the function object returned by bind().
324 
325 // Return the stored reference from reference_wrapper
326 template<typename T, typename... Args>
327 inline T& mu(reference_wrapper<T>& bound_arg, const tuple<Args&...>&)
328 {
329   return bound_arg.get();
330 }
331 
332 // Unwrap a tuple into separate arguments and forward to the function
333 // object f.
334 template<typename F, int... Indexes, typename... Args>
335 inline typename F::result_type
336 unwrap_and_forward(F& f, int_tuple<Indexes...>, const tuple<Args&...>& args)
337 {
338   return f(get<Indexes>(args)...);
339 }
340 
341 // Evaluate the inner bind expression
342 template<typename Bound, typename... Args>
343 inline typename enable_if<is_bind_expression<Bound>::value,
344                           typename Bound::result_type>::type
345 mu(Bound& bound_arg, const tuple<Args&...>& args)
346 {
347   typedef typename make_indexes<Args...>::type Indexes;
348   return unwrap_and_forward(bound_arg, Indexes(), args);
349 }
350 
351 // Retrieve the Ith argument from args
352 template<typename Bound, typename... Args>
353 inline typename safe_tuple_element<is_placeholder<Bound>::value - 1,
354                                    tuple<Args...> >::type
355 mu(Bound& bound_arg, const tuple<Args&...>& args)
356 {
357   return get<is_placeholder<Bound>::value-1>(args);
358 }
359 
360 // Return the stored value.
361 template<typename T>
362 struct is_reference_wrapper {
363   static const bool value = false;
364 };
365 
366 template<typename T>
367 struct is_reference_wrapper<reference_wrapper<T> > {
368   static const bool value = true;
369 };
370 
371 template<typename Bound, typename... Args>
372 inline typename enable_if<(!is_bind_expression<Bound>::value
373                            && !is_placeholder<Bound>::value
374                            && !is_reference_wrapper<Bound>::value),
375                           Bound&>::type
376 mu(Bound& bound_arg, const tuple<Args&...>&)
377 {
378   return bound_arg;
379 }
380 
381 //
382 template<typename F, typename... BoundArgs, int... Indexes, typename... Args>
383 typename F::result_type
384 apply_functor(F& f, tuple<BoundArgs...>& bound_args, int_tuple<Indexes...>,
385               const tuple<Args&...>& args)
386 {
387   return f(mu(get<Indexes>(bound_args), args)...);
388 }
389 
390 template<typename F, typename... BoundArgs>
391 class bound_functor
392 {
393   typedef typename make_indexes<BoundArgs...>::type indexes;
394 
395  public:
396   typedef typename F::result_type result_type;
397 
398   explicit bound_functor(const F& f, const BoundArgs&... bound_args)
399     : f(f), bound_args(bound_args...) { }
400 
401   template<typename... Args>
402   typename F::result_type operator()(Args&... args) {
403     return apply_functor(f, bound_args, indexes(), tie(args...));
404   }
405 
406  private:
407   F f;
408   tuple<BoundArgs...> bound_args;
409 };
410 
411 template<typename F, typename... BoundArgs>
412 struct is_bind_expression<bound_functor<F, BoundArgs...> > {
413   static const bool value = true;
414 };
415 
416 template<typename F, typename... BoundArgs>
417 inline bound_functor<F, BoundArgs...>
418 bind(const F& f, const BoundArgs&... bound_args)
419 {
420   return bound_functor<F, BoundArgs...>(f, bound_args...);
421 }
422 
423 
424 // 3.6.4 Placeholders
425 template<int I>
426 struct is_placeholder<placeholder<I> > {
427   static const int value = I;
428 };
429 
430 placeholder<1> _1;
431 placeholder<2> _2;
432 placeholder<3> _3;
433 placeholder<4> _4;
434 placeholder<5> _5;
435 placeholder<6> _6;
436 placeholder<7> _7;
437 placeholder<8> _8;
438 placeholder<9> _9;
439 
440 // Test code
441 template<typename T>
442 struct plus {
443   typedef T result_type;
444 
445   T operator()(T x, T y) { return x + y; }
446 };
447 
448 template<typename T>
449 struct multiplies {
450   typedef T result_type;
451 
452   T operator()(T x, T y) { return x * y; }
453 };
454 
455 template<typename T>
456 struct negate {
457   typedef T result_type;
458 
459   T operator()(T x) { return -x; }
460 };
461 
462 int main()
463 {
464   int seventeen = 17;
465   int forty_two = 42;
466 
467   assert(bind(plus<int>(), _1, _2)(seventeen, forty_two) == 59);
468   assert(bind(plus<int>(), _1, _1)(seventeen, forty_two) == 34);
469   assert(bind(plus<int>(), _2, _1)(seventeen, forty_two) == 59);
470   assert(bind(plus<int>(), 5, _1)(seventeen, forty_two) == 22);
471   assert(bind(plus<int>(), ref(seventeen), _2)(seventeen, forty_two) == 59);
472   assert(bind(plus<int>(), bind(multiplies<int>(), 3, _1), _2)(seventeen, forty_two)
473          == 93);
474   return 0;
475 }
476