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source: downloads/boost_1_34_1/libs/mpl/doc/src/refmanual/protect.rst @ 29

Last change on this file since 29 was 29, checked in by landauf, 17 years ago

updated boost from 1_33_1 to 1_34_1
File size: 2.1 KB

protect

Synopsis

template<
      typename F
    >
struct protect
{
    // |unspecified|
    // |...|
};

Description

protect is an identity wrapper for a |Metafunction Class| that prevents its argument from being recognized as a |bind expression|.

Parameters

Parameter Requirement Description
F |Metafunction Class| A metafunction class to wrap.

Expression semantics

For any |Metafunction Class| f:

typedef protect<f> g;
Return type:

|Metafunction Class|.
Semantics:

If f is a |bind expression|, equivalent to

struct g
{
    template<
          typename U1 = |unspecified|,|...| typename Un = |unspecified|
        >
    struct apply
        : apply_wrapn<f,U1,|...|Un>
    {
    };
};

otherwise equivalent to typedef f g;.

Example

FIXME
struct f
{
    template< typename T1, typename T2 > struct apply
    {
        // |...|
    };
};
typedef bind<_1, protect< bind<f,_1,_2> > >
typedef apply_wrap0< f0 >::type r1;
typedef apply_wrap0< g0 >::type r2;
typedef apply_wrap2< f2,int,char >::type r3;
BOOST_MPL_ASSERT(( is_same<r1,char> ));
BOOST_MPL_ASSERT(( is_same<r2,char> ));
BOOST_MPL_ASSERT(( is_same<r3,char> ));

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