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#### prior

###### Description

Returns the type of the previous iterator in a sequence.

###### Synopsis

    template<
        typename I
        >
    struct prior
    {
        typedef unspecified type;
    };

Table 1.15. Parameters

Parameter | Requirement | Description
--- | --- | ---
`I` | Model of Bidirectional Iterator | Operation's argument

###### Expression Semantics

    result_of::prior<I>::type

Return type: A model of the same iterator concept as `I`.

Semantics: Returns an iterator to the previous element in the sequence before `I`.

###### Header

    #include <boost/fusion/iterator/prior.hpp>
    #include <boost/fusion/include/prior.hpp>

###### Example

    typedef vector<int,double> vec;
    typedef result_of::next<result_of::begin<vec>::type>::type second;

    BOOST_MPL_ASSERT((boost::is_same<result_of::value_of<second>::type, double>));

    typedef result_of::prior<second>::type first;
    BOOST_MPL_ASSERT((boost::is_same<result_of::value_of<first>::type, int>));