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// { dg-do run }
// { dg-options "-std=gnu++0x" }
// A basic implementation of TR1's bind using variadic teplates
// Contributed by Douglas Gregor <doug.gregor@gmail.com>
#include <cassert>
// Trivial reference_wrapper
template<typename T>
struct reference_wrapper
{
reference_wrapper(T& x) : ptr(&x) { }
operator T&() const { return *ptr; }
T& get() const { return *ptr; }
T* ptr;
};
template<typename T> reference_wrapper<T> ref(T& x) { return x; }
template<typename T> reference_wrapper<const T> cref(const T& x) { return x; }
// Simple type-traits we'll need
template<typename T>
struct add_reference
{
typedef T& type;
};
template<typename T>
struct add_reference<T&>
{
typedef T& type;
};
template<typename T, typename U>
struct is_same
{
static const bool value = false;
};
template<typename T>
struct is_same<T, T>
{
static const bool value = true;
};
// For creating the constructor parameters of tuple<>
template<typename T>
struct add_const_reference
{
typedef const T& type;
};
template<typename T>
struct add_const_reference<T&>
{
typedef T& type;
};
// 6.1.3 Class template tuple: Needed for bind() implementation
template<typename... Values>
class tuple;
template<> class tuple<> { };
template<typename Head, typename... Tail>
class tuple<Head, Tail...>
: private tuple<Tail...>
{
typedef tuple<Tail...> inherited;
public:
tuple() { }
// implicit copy-constructor is okay
tuple(typename add_const_reference<Head>::type v,
typename add_const_reference<Tail>::type... vtail)
: m_head(v), inherited(vtail...) { }
template<typename... VValues>
tuple(const tuple<VValues...>& other)
: m_head(other.head()), inherited(other.tail()) { }
template<typename... VValues>
tuple& operator=(const tuple<VValues...>& other)
{
m_head = other.head();
tail() = other.tail();
return *this;
}
typename add_reference<Head>::type head() { return m_head; }
typename add_reference<const Head>::type head() const { return m_head; }
inherited& tail() { return *this; }
const inherited& tail() const { return *this; }
protected:
Head m_head;
};
template<typename T>
struct make_tuple_result
{
typedef T type;
};
template<typename T>
struct make_tuple_result<reference_wrapper<T> >
{
typedef T& type;
};
// 6.1.3.2 Tuple creation functions
struct ignore_t {
template<typename T> ignore_t& operator=(const T&) { return *this; }
} ignore;
template<typename... Values>
tuple<typename make_tuple_result<Values>::type...>
make_tuple(const Values&... values)
{
return tuple<typename make_tuple_result<Values>::type...>(values...);
}
template<typename... Values>
tuple<Values&...> tie(Values&... values)
{
return tuple<Values&...>(values...);
}
// 6.1.3.3 Tuple helper classes
template<typename Tuple>
struct tuple_size;
template<>
struct tuple_size<tuple<> >
{
static const __SIZE_TYPE__ value = 0;
};
template<typename Head, typename... Tail>
struct tuple_size<tuple<Head, Tail...> >
{
static const __SIZE_TYPE__ value = 1 + tuple_size<tuple<Tail...> >::value;
};
template<int I, typename Tuple>
struct tuple_element;
template<int I, typename Head, typename... Tail>
struct tuple_element<I, tuple<Head, Tail...> >
{
typedef typename tuple_element<I-1, tuple<Tail...> >::type type;
};
template<typename Head, typename... Tail>
struct tuple_element<0, tuple<Head, Tail...> >
{
typedef Head type;
};
// 6.1.3.4 Element access
template<int I, typename Tuple>
class get_impl;
template<int I, typename Head, typename... Values>
class get_impl<I, tuple<Head, Values...> >
{
typedef typename tuple_element<I-1, tuple<Values...> >::type Element;
typedef typename add_reference<Element>::type RJ;
typedef typename add_const_reference<Element>::type PJ;
typedef get_impl<I-1, tuple<Values...> > Next;
public:
static RJ get(tuple<Head, Values...>& t)
{ return Next::get(t.tail()); }
static PJ get(const tuple<Head, Values...>& t)
{ return Next::get(t.tail()); }
};
template<typename Head, typename... Values>
class get_impl<0, tuple<Head, Values...> >
{
typedef typename add_reference<Head>::type RJ;
typedef typename add_const_reference<Head>::type PJ;
public:
static RJ get(tuple<Head, Values...>& t) { return t.head(); }
static PJ get(const tuple<Head, Values...>& t) { return t.head(); }
};
template<int I, typename... Values>
typename add_reference<
typename tuple_element<I, tuple<Values...> >::type
>::type
get(tuple<Values...>& t)
{
return get_impl<I, tuple<Values...> >::get(t);
}
template<int I, typename... Values>
typename add_const_reference<
typename tuple_element<I, tuple<Values...> >::type
>::type
get(const tuple<Values...>& t)
{
return get_impl<I, tuple<Values...> >::get(t);
}
// 6.1.3.5 Relational operators
inline bool operator==(const tuple<>&, const tuple<>&) { return true; }
template<typename T, typename... TTail, typename U, typename... UTail>
bool operator==(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u)
{
return t.head() == u.head() && t.tail() == u.tail();
}
template<typename... TValues, typename... UValues>
bool operator!=(const tuple<TValues...>& t, const tuple<UValues...>& u)
{
return !(t == u);
}
inline bool operator<(const tuple<>&, const tuple<>&) { return false; }
template<typename T, typename... TTail, typename U, typename... UTail>
bool operator<(const tuple<T, TTail...>& t, const tuple<U, UTail...>& u)
{
return (t.head() < u.head() ||
(!(t.head() < u.head()) && t.tail() < u.tail()));
}
template<typename... TValues, typename... UValues>
bool operator>(const tuple<TValues...>& t, const tuple<UValues...>& u)
{
return u < t;
}
template<typename... TValues, typename... UValues>
bool operator<=(const tuple<TValues...>& t, const tuple<UValues...>& u)
{
return !(u < t);
}
template<typename... TValues, typename... UValues>
bool operator>=(const tuple<TValues...>& t, const tuple<UValues...>& u)
{
return !(t < u);
}
// enable_if, the breakfast of champions
template<bool Cond, typename Type = void>
struct enable_if {
typedef Type type;
};
template<typename Type>
struct enable_if<false, Type> { };
// 3.6 Function object binders
// 3.6.1 Class template is_bind_expression
template<typename T>
struct is_bind_expression {
static const bool value = false;
};
// 3.6.2 Class template is_placeholder
template<typename T>
struct is_placeholder {
static const int value = 0;
};
// 3.6.3 Function template bind
template<int I> struct placeholder {} ;
template<int N> struct int_c { };
// A tuple of integer values
template<int...> struct int_tuple {};
// make_indexes_impl is a helper for make_indexes
template<int I, typename IntTuple, typename... Types>
struct make_indexes_impl;
template<int I, int... Indexes, typename T, typename... Types>
struct make_indexes_impl<I, int_tuple<Indexes...>, T, Types...>
{
typedef typename make_indexes_impl<I+1,
int_tuple<Indexes..., I>,
Types...>::type type;
};
template<int I, int... Indexes>
struct make_indexes_impl<I, int_tuple<Indexes...> > {
typedef int_tuple<Indexes...> 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<typename... Types>
struct make_indexes : make_indexes_impl<0, int_tuple<>, Types...> { };
// Get the Ith tuple element, but only if I is in bounds.
template<int I, typename Tuple, typename = void>
struct safe_tuple_element{ };
template<int I, typename... Values>
struct safe_tuple_element<I, tuple<Values...>,
typename enable_if<(I >= 0 &&
I < tuple_size<tuple<Values...> >::value)
>::type>
{
typedef typename tuple_element<I, tuple<Values...> >::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<typename T, typename... Args>
inline T& mu(reference_wrapper<T>& bound_arg, const tuple<Args&...>&)
{
return bound_arg.get();
}
// Unwrap a tuple into separate arguments and forward to the function
// object f.
template<typename F, int... Indexes, typename... Args>
inline typename F::result_type
unwrap_and_forward(F& f, int_tuple<Indexes...>, const tuple<Args&...>& args)
{
return f(get<Indexes>(args)...);
}
// Evaluate the inner bind expression
template<typename Bound, typename... Args>
inline typename enable_if<is_bind_expression<Bound>::value,
typename Bound::result_type>::type
mu(Bound& bound_arg, const tuple<Args&...>& args)
{
typedef typename make_indexes<Args...>::type Indexes;
return unwrap_and_forward(bound_arg, Indexes(), args);
}
// Retrieve the Ith argument from args
template<typename Bound, typename... Args>
inline typename safe_tuple_element<is_placeholder<Bound>::value - 1,
tuple<Args...> >::type
mu(Bound& bound_arg, const tuple<Args&...>& args)
{
return get<is_placeholder<Bound>::value-1>(args);
}
// Return the stored value.
template<typename T>
struct is_reference_wrapper {
static const bool value = false;
};
template<typename T>
struct is_reference_wrapper<reference_wrapper<T> > {
static const bool value = true;
};
template<typename Bound, typename... Args>
inline typename enable_if<(!is_bind_expression<Bound>::value
&& !is_placeholder<Bound>::value
&& !is_reference_wrapper<Bound>::value),
Bound&>::type
mu(Bound& bound_arg, const tuple<Args&...>&)
{
return bound_arg;
}
//
template<typename F, typename... BoundArgs, int... Indexes, typename... Args>
typename F::result_type
apply_functor(F& f, tuple<BoundArgs...>& bound_args, int_tuple<Indexes...>,
const tuple<Args&...>& args)
{
return f(mu(get<Indexes>(bound_args), args)...);
}
template<typename F, typename... BoundArgs>
class bound_functor
{
typedef typename make_indexes<BoundArgs...>::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... Args>
typename F::result_type operator()(Args&... args) {
return apply_functor(f, bound_args, indexes(), tie(args...));
}
private:
F f;
tuple<BoundArgs...> bound_args;
};
template<typename F, typename... BoundArgs>
struct is_bind_expression<bound_functor<F, BoundArgs...> > {
static const bool value = true;
};
template<typename F, typename... BoundArgs>
inline bound_functor<F, BoundArgs...>
bind(const F& f, const BoundArgs&... bound_args)
{
return bound_functor<F, BoundArgs...>(f, bound_args...);
}
// 3.6.4 Placeholders
template<int I>
struct is_placeholder<placeholder<I> > {
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<typename T>
struct plus {
typedef T result_type;
T operator()(T x, T y) { return x + y; }
};
template<typename T>
struct multiplies {
typedef T result_type;
T operator()(T x, T y) { return x * y; }
};
template<typename T>
struct negate {
typedef T result_type;
T operator()(T x) { return -x; }
};
int main()
{
int seventeen = 17;
int forty_two = 42;
assert(bind(plus<int>(), _1, _2)(seventeen, forty_two) == 59);
assert(bind(plus<int>(), _1, _1)(seventeen, forty_two) == 34);
assert(bind(plus<int>(), _2, _1)(seventeen, forty_two) == 59);
assert(bind(plus<int>(), 5, _1)(seventeen, forty_two) == 22);
assert(bind(plus<int>(), ref(seventeen), _2)(seventeen, forty_two) == 59);
assert(bind(plus<int>(), bind(multiplies<int>(), 3, _1), _2)(seventeen, forty_two)
== 93);
return 0;
}
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