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Coding Standards
Front Page / Sequences / Intrinsic Metafunctions / empty |
Returns an Integral Constant c such that c::value == true if and only if the sequence is empty.
#include <boost/mpl/empty.hpp>
Parameter | Requirement | Description |
---|---|---|
Sequence | Forward Sequence | A sequence to test. |
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 ). |
Amortized constant time.
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> );