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source: downloads/boost_1_33_1/libs/mpl/doc/src/refmanual/empty.rst @ 12

Last change on this file since 12 was 12, checked in by landauf, 17 years ago

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empty

Synopsis

template<
      typename Sequence
    >
struct empty
{
    typedef |unspecified| type;
};

Description

Returns an |Integral Constant| c such that c::value == true if and only if the sequence is empty.

Parameters

Parameter Requirement Description
Sequence |Forward Sequence| A sequence to test.

Expression semantics

For any |Forward Sequence| s:

typedef empty<s>::type c;
Return type:Boolean |Integral Constant|.
Semantics:Equivalent to typedef is_same< begin<s>::type,end<s>::type >::type c;.
Postcondition:empty<s>::value == ( size<s>::value == 0 ).

Complexity

Amortized constant time.

Example

typedef range_c<int,0,0> empty_range;
typedef vector<long,float,double> types;
BOOST_MPL_ASSERT( empty<empty_range> );
BOOST_MPL_ASSERT_NOT( empty<types> );

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