Front Page / Sequences / Intrinsic Metafunctions / clear

# clear

### Synopsis

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

### Description

Returns an empty sequence concept-identical to `Sequence`.

### Header

    #include <boost/mpl/clear.hpp>

### Model of

Tag Dispatched Metafunction

### Parameters

Parameter | Requirement | Description
--- | --- | ---
`Sequence` | Extensible Sequence or Extensible Associative Sequence | A sequence to get an empty "copy" of.

### Expression semantics

For any Extensible Sequence or Extensible Associative Sequence `s`:

    typedef clear<s>::type t;

Return type: | Extensible Sequence or Extensible Associative Sequence.

Semantics:

Equivalent to

    typedef erase< s, begin<s>::type, end<s>::type >::type t;

Postcondition: | `empty<s>::value == true`.

### Complexity

Amortized constant time.

### Example

    typedef vector_c<int,1,3,5,7,9,11> odds;
    typedef clear<odds>::type nothing;

    BOOST_MPL_ASSERT(( empty<nothing> ));

### See also

Extensible Sequence, Extensible Associative Sequence, erase, empty, begin, end