Front Page / Iterators / Iterator Metafunctions / prior

# prior

### Synopsis

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

### Description

Returns the previous iterator in the sequence. [Note: `prior` has a number of overloaded meanings, depending on the type of its argument. For instance, if `X` is an Integral Constant, `prior<X>` returns an decremented Integral Constant of the same type. The following specification is iterator-specific. Please refer to the corresponding concept's documentation for the details of the alternative semantics — end note].

### Header

    #include <boost/mpl/next_prior.hpp>

### Parameters

Parameter | Requirement | Description
--- | --- | ---
`Iterator` | Forward Iterator. | An iterator to decrement.

### Expression semantics

For any Forward Iterators `iter`:

    typedef prior<iter>::type j;

Return type: | Forward Iterator.
Precondition: | `iter` is decrementable.

Semantics:

`j` is an iterator pointing to the previous element in the sequence. If `iter` is a user-defined iterator, the library-provided default implementation is equivalent to

    typedef iter::prior j;

### Complexity

Amortized constant time.

### Example

    typedef vector_c<int,1> v;
    typedef begin<v>::type first;
    typedef end<v>::type last;

    BOOST_MPL_ASSERT(( is_same< prior<last>::type, first > ));

### See also

Iterators, `begin` / `end`, `next`, `deref`