[section:replace_if replace_if]

[heading 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);
``

[heading Description]

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

[heading Definition]

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

[heading 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`.

[heading Complexity]

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

[endsect]