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##### replace_if

###### Description

Replaces each element of a given sequence for which an unary function object evaluates to `true` replaced with a new value.

###### Synopsis

    template<
        typename Sequence,
        typename F,
        typename T>
    typename result_of::replace_if<Sequence const, F, T>::type replace_if(
        Sequence const& seq, F f, T const& new_value);

Table 1.69. Parameters

Parameter | Requirement | Description
--- | --- | ---
`seq` | A model of Forward Sequence | Operation's argument
`f` | A function object for which `f(e)` is a valid expression, convertible to `bool`, for each element `e` in `seq` | Operation's argument
`new_value` | Any type | Replacement value

###### Expression Semantics

    replace_if(seq, f, new_value);

Return type: A model of Forward Sequence.

Semantics: Returns a new sequence with all the elements of `seq`, with `new_value` assigned to each element for which `f` evaluates to `true`.

###### Complexity

Constant. Returns a view which is lazily evaluated.

###### Header

    #include <boost/fusion/algorithm/transformation/replace_if.hpp>
    #include <boost/fusion/include/replace_if.hpp>

###### Example

    struct odd
    {
        template<typename T>
        bool operator()(T t) const
        {
            return t % 2;
        }
    };
    ...
    assert(replace_if(make_vector(1,2), odd(), 3) == make_vector(3,2));