always

Synopsis

template< 
      typename X
    >
struct always
{
    // unspecified
    // ...
};

Description

always<X> specialization is a variadic Metafunction Class always returning the same type, X, regardless of the number and types of passed arguments.

Header

#include <boost/mpl/always.hpp>

Model of

Metafunction Class

Parameters

Parameter	Requirement	Description
`X`	Any type	A type to be returned.

Expression semantics

For an arbitrary type x:

typedef always<x> f;

Return type: Metafunction Class.

Semantics:

Return type:	Metafunction Class.
Semantics:	Equivalent to struct f : bind< identity<_1>, x > {};

Equivalent to

struct f : bind< identity<_1>, x > {};

Example

typedef always<true_> always_true;

BOOST_MPL_ASSERT(( apply< always_true,false_> ));
BOOST_MPL_ASSERT(( apply< always_true,false_,false_ > ));
BOOST_MPL_ASSERT(( apply< always_true,false_,false_,false_ > ));