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

Complexity

Amortized constant time.

Example

typedef range_c empty_range;
typedef vector types;

BOOST_MPL_ASSERT( empty );
BOOST_MPL_ASSERT_NOT( empty );
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Copyright © 2001-2009 Aleksey Gurtovoy and David Abrahams
Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)