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# reverse_transform

### Synopsis

    template<
          typename Seq
        , typename Op
        , typename In = unspecified
        >
    struct reverse_transform
    {
        typedef unspecified type;
    };

    template<
          typename Seq1
        , typename Seq2
        , typename BinaryOp
        , typename In = unspecified
        >
    struct reverse_transform
    {
        typedef unspecified type;
    };

### Description

`reverse_transform` is an overloaded name:

- `reverse_transform<Seq,Op>` returns a reversed, transformed copy of the original sequence produced by applying an unary transformation `Op` to every element in the [`begin<Sequence>::type`, `end<Sequence>::type`) range.
- `reverse_transform<Seq1,Seq2,Op>` returns a new sequence produced by applying a binary transformation `BinaryOp` to a pair of elements (e1, e21) from the corresponding [`begin<Seq1>::type`, `end<Seq1>::type`) and [`begin<Seq2>::type`, `end<Seq2>::type`) ranges in reverse order.

[Note: This wording applies to a no-inserter version(s) of the algorithm. See the Expression semantics subsection for a precise specification of the algorithm's details in all cases — end note]

### Header

    #include <boost/mpl/transform.hpp>

### Model of

Reversible Algorithm

### Parameters

Parameter | Requirement | Description
--- | --- | ---
`Sequence`, `Seq1`, `Seq2` | Forward Sequence | Sequences to transform.
`Op`, `BinaryOp` | Lambda Expression | A transformation.
`In` | Inserter | An inserter.

### Expression semantics

The semantics of an expression are defined only where they differ from, or are not defined in Reversible Algorithm.

For any Forward Sequences `s`, `s1` and `s2`, Lambda Expressions `op` and `op2`, and an Inserter `in`:

    typedef reverse_transform<s,op,in>::type r;

Return type: | A type.
Postcondition: | Equivalent to
    typedef lambda<op>::type f;
    typedef lambda<in::operation>::type in_op;

    typedef reverse_fold<
          s
        , in::state
        , bind< in_op, _1, bind<f, _2> >
        >::type r;

    typedef transform<s1,s2,op,in>::type r;

Return type: | A type.
Postcondition: | Equivalent to
    typedef lambda<op2>::type f;
    typedef lambda<in::operation>::type in_op;

    typedef reverse_fold<
          pair_view<s1,s2>
        , in::state
        , bind<
              in_op
            , _1
            , bind<f, bind<first<>,_2>, bind<second<>,_2> >
            >
        >::type r;

### Complexity

Linear. Exactly `size<s>::value` / `size<s1>::value` applications of `op` / `op2` and `in::operation`.

### Example

    typedef vector<char,short,int,long,float,double> types;
    typedef vector<double*,float*,long*,int*,short*,char*> pointers;
    typedef reverse_transform< types,boost::add_pointer<_1> >::type result;

    BOOST_MPL_ASSERT(( equal<result,pointers> ));

### See also

Transformation Algorithms, Reversible Algorithm, transform, reverse_copy, replace_if