order

Synopsis

template<
      typename Sequence
    , typename Key
    >
struct order
{
    typedef unspecified type;
};

Description

Returns a unique unsigned Integral Constant associated with the key Key in Sequence.

Header

#include <boost/mpl/order.hpp>

Model of

Tag Dispatched Metafunction

Parameters

Parameter	Requirement	Description
`Sequence`	Associative Sequence	A sequence to query.
`Key`	Any type	The queried key.

Expression semantics

For any Associative Sequence s, and arbitrary type key:

typedef order<s,key>::type n;

Return type:	Unsigned Integral Constant.
Semantics:	If `has_key<s,key>::value == true`, `n` is a unique unsigned Integral Constant associated with `key` in `s`; otherwise, `n` is identical to `void_`.

Complexity

Amortized constant time.

Example

typedef map< pair<int,unsigned>, pair<char,long> > m;

BOOST_MPL_ASSERT_NOT(( is_same< order<m,int>::type, void_ > ));
BOOST_MPL_ASSERT(( is_same< order<m,long>::type,void_ > ));