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##### replace_if

###### Prototype

    template<class ForwardRange, class UnaryPredicate, class Value>
    ForwardRange& replace_if(ForwardRange& rng, UnaryPredicate pred, const Value& with_what);

    template<class ForwardRange, class UnaryPredicate, class Value>
    const ForwardRange& replace_if(const ForwardRange& rng, UnaryPredicate pred, const Value& with_what);

###### Description

`replace_if` replaces every element `x` in `rng` for which `pred(x) == true` with `with_what`. Returns a reference to `rng`.

###### Definition

Defined in the header file `boost/range/algorithm/replace_if.hpp`

###### Requirements

- `ForwardRange` is a model of the Forward Range Concept.
- `ForwardRange` is mutable.
- `UnaryPredicate` is a model of the `PredicateConcept`
- `ForwardRange`'s value type is convertible to `UnaryPredicate`'s argument type.
- `Value` is convertible to `ForwardRange`'s value type.
- `Value` is a model of the `AssignableConcept`.

###### Complexity

Linear. `replace_if` performs exactly `distance(rng)` applications of `pred`, and at most `distance(rng)` assignments.