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