template<
typename F
>
struct bind0
{
// unspecified
// ...
};
template<
typename F, typename A1
>
struct bind1
{
// unspecified
// ...
};
...
template<
typename F, typename A1,... typename An
>
struct bindn
{
// unspecified
// ...
};
template<
typename F
, typename A1 = unspecified
...
, typename An = unspecified
>
struct bind
{
// unspecified
// ...
};
bind is a higher-order primitive for Metafunction Class composition
and argument binding. In essence, it's a compile-time counterpart of
the similar run-time functionality provided by Boost.Bind and Boost.Lambda
libraries.
Parameter |
Requirement |
Description |
F |
Metafunction Class |
An metafunction class to perform binding on. |
A1,... An |
Any type |
Arguments to bind. |
For any Metafunction Class f and arbitrary types a1,... an:
typedef bind<f,a1,...an> g;
typedef bindn<f,a1,...an> g;
Semantics: | Equivalent to
struct g
{
template<
typename U1 = unspecified
...
, typename Un = unspecified
>
struct apply
: apply_wrapn<
typename h0<f,U1,...Un>::type
, typename h1<a1,U1,...Un>::type
...
, typename hn<an,U1,...Un>::type
>
{
};
};
where hk is equivalent to
template< typename X, typename U1,... typename Un > struct hk
: apply_wrapn<X,U1,...Un>
{
};
if f or ak is a bind expression or a placeholder, and
template< typename X, typename U1,... typename Un > struct hk
{
typedef X type;
};
otherwise. [Note: Every nth appearance of the unnamed placeholder
in the bind<f,a1,...an> specialization is replaced with the corresponding
numbered placeholder _n — end note]
|
struct f1
{
template< typename T1 > struct apply
{
typedef T1 type;
};
};
struct f5
{
template< typename T1, typename T2, typename T3, typename T4, typename T5 >
struct apply
{
typedef T5 type;
};
};
typedef apply_wrap1<
bind1<f1,_1>
, int
>::type r11;
typedef apply_wrap5<
bind1<f1,_5>
, void,void,void,void,int
>::type r12;
BOOST_MPL_ASSERT(( is_same<r11,int> ));
BOOST_MPL_ASSERT(( is_same<r12,int> ));
typedef apply_wrap5<
bind5<f5,_1,_2,_3,_4,_5>
, void,void,void,void,int
>::type r51;
typedef apply_wrap5<
bind5<f5,_5,_4,_3,_2,_1>
, int,void,void,void,void
>::type r52;
BOOST_MPL_ASSERT(( is_same<r51,int> ));
BOOST_MPL_ASSERT(( is_same<r52,int> ));
|