// { dg-do run } // { dg-options "-std=gnu++0x" } // A basic implementation of TR1's bind using variadic teplates // Contributed by Douglas Gregor #include // Trivial reference_wrapper template struct reference_wrapper { reference_wrapper(T& x) : ptr(&x) { } operator T&() const { return *ptr; } T& get() const { return *ptr; } T* ptr; }; template reference_wrapper ref(T& x) { return x; } template reference_wrapper cref(const T& x) { return x; } // Simple type-traits we'll need template struct add_reference { typedef T& type; }; template struct add_reference { typedef T& type; }; template struct is_same { static const bool value = false; }; template struct is_same { static const bool value = true; }; // For creating the constructor parameters of tuple<> template struct add_const_reference { typedef const T& type; }; template struct add_const_reference { typedef T& type; }; // 6.1.3 Class template tuple: Needed for bind() implementation template class tuple; template<> class tuple<> { }; template class tuple : private tuple { typedef tuple inherited; public: tuple() { } // implicit copy-constructor is okay tuple(typename add_const_reference::type v, typename add_const_reference::type... vtail) : m_head(v), inherited(vtail...) { } template tuple(const tuple& other) : m_head(other.head()), inherited(other.tail()) { } template tuple& operator=(const tuple& other) { m_head = other.head(); tail() = other.tail(); return *this; } typename add_reference::type head() { return m_head; } typename add_reference::type head() const { return m_head; } inherited& tail() { return *this; } const inherited& tail() const { return *this; } protected: Head m_head; }; template struct make_tuple_result { typedef T type; }; template struct make_tuple_result > { typedef T& type; }; // 6.1.3.2 Tuple creation functions struct ignore_t { template ignore_t& operator=(const T&) { return *this; } } ignore; template tuple::type...> make_tuple(const Values&... values) { return tuple::type...>(values...); } template tuple tie(Values&... values) { return tuple(values...); } // 6.1.3.3 Tuple helper classes template struct tuple_size; template<> struct tuple_size > { static const __SIZE_TYPE__ value = 0; }; template struct tuple_size > { static const __SIZE_TYPE__ value = 1 + tuple_size >::value; }; template struct tuple_element; template struct tuple_element > { typedef typename tuple_element >::type type; }; template struct tuple_element<0, tuple > { typedef Head type; }; // 6.1.3.4 Element access template class get_impl; template class get_impl > { typedef typename tuple_element >::type Element; typedef typename add_reference::type RJ; typedef typename add_const_reference::type PJ; typedef get_impl > Next; public: static RJ get(tuple& t) { return Next::get(t.tail()); } static PJ get(const tuple& t) { return Next::get(t.tail()); } }; template class get_impl<0, tuple > { typedef typename add_reference::type RJ; typedef typename add_const_reference::type PJ; public: static RJ get(tuple& t) { return t.head(); } static PJ get(const tuple& t) { return t.head(); } }; template typename add_reference< typename tuple_element >::type >::type get(tuple& t) { return get_impl >::get(t); } template typename add_const_reference< typename tuple_element >::type >::type get(const tuple& t) { return get_impl >::get(t); } // 6.1.3.5 Relational operators inline bool operator==(const tuple<>&, const tuple<>&) { return true; } template bool operator==(const tuple& t, const tuple& u) { return t.head() == u.head() && t.tail() == u.tail(); } template bool operator!=(const tuple& t, const tuple& u) { return !(t == u); } inline bool operator<(const tuple<>&, const tuple<>&) { return false; } template bool operator<(const tuple& t, const tuple& u) { return (t.head() < u.head() || (!(t.head() < u.head()) && t.tail() < u.tail())); } template bool operator>(const tuple& t, const tuple& u) { return u < t; } template bool operator<=(const tuple& t, const tuple& u) { return !(u < t); } template bool operator>=(const tuple& t, const tuple& u) { return !(t < u); } // enable_if, the breakfast of champions template struct enable_if { typedef Type type; }; template struct enable_if { }; // 3.6 Function object binders // 3.6.1 Class template is_bind_expression template struct is_bind_expression { static const bool value = false; }; // 3.6.2 Class template is_placeholder template struct is_placeholder { static const int value = 0; }; // 3.6.3 Function template bind template struct placeholder {} ; template struct int_c { }; // A tuple of integer values template struct int_tuple {}; // make_indexes_impl is a helper for make_indexes template struct make_indexes_impl; template struct make_indexes_impl, T, Types...> { typedef typename make_indexes_impl, Types...>::type type; }; template struct make_indexes_impl > { typedef int_tuple type; }; // make_indexes takes a variable-length number of N types and // generates an int_tuple that contains <0, 1, 2, ..., N-1>. These can // be used as indexes for tuple's get or tuple_element operation. template struct make_indexes : make_indexes_impl<0, int_tuple<>, Types...> { }; // Get the Ith tuple element, but only if I is in bounds. template struct safe_tuple_element{ }; template struct safe_tuple_element, typename enable_if<(I >= 0 && I < tuple_size >::value) >::type> { typedef typename tuple_element >::type type; }; // mu maps a bound argument to an actual argument, given a tuple of // the arguments passed to the function object returned by bind(). // Return the stored reference from reference_wrapper template inline T& mu(reference_wrapper& bound_arg, const tuple&) { return bound_arg.get(); } // Unwrap a tuple into separate arguments and forward to the function // object f. template inline typename F::result_type unwrap_and_forward(F& f, int_tuple, const tuple& args) { return f(get(args)...); } // Evaluate the inner bind expression template inline typename enable_if::value, typename Bound::result_type>::type mu(Bound& bound_arg, const tuple& args) { typedef typename make_indexes::type Indexes; return unwrap_and_forward(bound_arg, Indexes(), args); } // Retrieve the Ith argument from args template inline typename safe_tuple_element::value - 1, tuple >::type mu(Bound& bound_arg, const tuple& args) { return get::value-1>(args); } // Return the stored value. template struct is_reference_wrapper { static const bool value = false; }; template struct is_reference_wrapper > { static const bool value = true; }; template inline typename enable_if<(!is_bind_expression::value && !is_placeholder::value && !is_reference_wrapper::value), Bound&>::type mu(Bound& bound_arg, const tuple&) { return bound_arg; } // template typename F::result_type apply_functor(F& f, tuple& bound_args, int_tuple, const tuple& args) { return f(mu(get(bound_args), args)...); } template class bound_functor { typedef typename make_indexes::type indexes; public: typedef typename F::result_type result_type; explicit bound_functor(const F& f, const BoundArgs&... bound_args) : f(f), bound_args(bound_args...) { } template typename F::result_type operator()(Args&... args) { return apply_functor(f, bound_args, indexes(), tie(args...)); } private: F f; tuple bound_args; }; template struct is_bind_expression > { static const bool value = true; }; template inline bound_functor bind(const F& f, const BoundArgs&... bound_args) { return bound_functor(f, bound_args...); } // 3.6.4 Placeholders template struct is_placeholder > { static const int value = I; }; placeholder<1> _1; placeholder<2> _2; placeholder<3> _3; placeholder<4> _4; placeholder<5> _5; placeholder<6> _6; placeholder<7> _7; placeholder<8> _8; placeholder<9> _9; // Test code template struct plus { typedef T result_type; T operator()(T x, T y) { return x + y; } }; template struct multiplies { typedef T result_type; T operator()(T x, T y) { return x * y; } }; template struct negate { typedef T result_type; T operator()(T x) { return -x; } }; int main() { int seventeen = 17; int forty_two = 42; assert(bind(plus(), _1, _2)(seventeen, forty_two) == 59); assert(bind(plus(), _1, _1)(seventeen, forty_two) == 34); assert(bind(plus(), _2, _1)(seventeen, forty_two) == 59); assert(bind(plus(), 5, _1)(seventeen, forty_two) == 22); assert(bind(plus(), ref(seventeen), _2)(seventeen, forty_two) == 59); assert(bind(plus(), bind(multiplies(), 3, _1), _2)(seventeen, forty_two) == 93); return 0; }