size

Synopsis

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

Description

size returns the number of elements in the sequence, that is, the number of elements in the range [begin<Sequence>::type, end<Sequence>::type).

Header

#include <boost/mpl/size.hpp>

Parameters

Parameter	Requirement	Description
`Sequence`	Forward Sequence	A sequence to query.

Return type:	Integral Constant.
Semantics:	Equivalent to typedef distance< begin<s>::type,end<s>::type >::type n;
Postcondition:	`n::value >= 0`.

Complexity

The complexity of the size metafunction directly depends on the implementation of the particular sequence it is applied to. In the worst case, size guarantees a linear complexity.

If the s is a Random Access Sequence, size<s>::type is an O(1) operation. The opposite is not necessarily true — for example, a sequence class that models Forward Sequence might still give us an O(1) size implementation.

Example

typedef list0<> empty_list;
typedef vector_c<int,0,1,2,3,4,5> numbers;
typedef range_c<int,0,100> more_numbers;

BOOST_MPL_ASSERT_RELATION( size<list>::value, ==, 0 );
BOOST_MPL_ASSERT_RELATION( size<numbers>::value, ==, 5 );
BOOST_MPL_ASSERT_RELATION( size<more_numbers>::value, ==, 100 );