lambda

Synopsis

template<
      typename X
    , typename Tag = unspecified
    >
struct lambda
{
    typedef unspecified type;
};

Description

If X is a Placeholder Expression, transforms X into a corresponding Metafunction Class, otherwise X is returned unchanged.

Header

#include <boost/mpl/lambda.hpp>

Parameters

Parameter	Requirement	Description
`X`	Any type	An expression to transform.
`Tag`	Any type	A tag determining transform semantics.

Expression semantics

For arbitrary types x and tag:

typedef lambda<x>::type f;

Return type:

Return type:	Metafunction Class.
Semantics:	If `x` is a Placeholder Expression in a general form `X<a1,...an>`, where `X` is a class template and `a1`,... `an` are arbitrary types, equivalent to typedef protect< bind< quoten<X> , lambda<a1>::type,... lambda<an>::type > > f; otherwise, `f` is identical to `x`.

Metafunction Class.

Semantics:

If x is a Placeholder Expression in a general form X<a1,...an>, where X is a class template and a1,... an are arbitrary types, equivalent to

typedef protect< bind<
      quoten<X>
    , lambda<a1>::type,... lambda<an>::type
    > > f;

otherwise, f is identical to x.

typedef lambda<x,tag>::type f;

Return type:

Return type:	Metafunction Class.
Semantics:	If `x` is a Placeholder Expression in a general form `X<a1,...an>`, where `X` is a class template and `a1`,... `an` are arbitrary types, equivalent to typedef protect< bind< quoten<X,tag> , lambda<a1,tag>::type,... lambda<an,tag>::type > > f; otherwise, `f` is identical to `x`.

Metafunction Class.

Semantics:

If x is a Placeholder Expression in a general form X<a1,...an>, where X is a class template and a1,... an are arbitrary types, equivalent to

typedef protect< bind<
      quoten<X,tag>
    , lambda<a1,tag>::type,... lambda<an,tag>::type
    > > f;

otherwise, f is identical to x.

Example

template< typename N1, typename N2 > struct int_plus
    : int_<( N1::value + N2::value )>
{
};

typedef lambda< int_plus<_1, int_<42> > >::type f1;
typedef bind< quote2<int_plus>, _1, int_<42> > f2;

typedef f1::apply<42>::type r1;
typedef f2::apply<42>::type r2;

BOOST_MPL_ASSERT_RELATION( r1::value, ==, 84 );
BOOST_MPL_ASSERT_RELATION( r2::value, ==, 84 );