# 27 Algorithms library [algorithms]

## 27.7 Mutating sequence operations [alg.modifying.operations]

### 27.7.5 Replace [alg.replace]

```template<class ForwardIterator, class T = iterator_traits<ForwardIterator>::value_type> constexpr void replace(ForwardIterator first, ForwardIterator last, const T& old_value, const T& new_value); template<class ExecutionPolicy, class ForwardIterator, class T = iterator_traits<ForwardIterator>::value_type> void replace(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, const T& old_value, const T& new_value); template<class ForwardIterator, class Predicate, class T = iterator_traits<ForwardIterator>::value_type> constexpr void replace_if(ForwardIterator first, ForwardIterator last, Predicate pred, const T& new_value); template<class ExecutionPolicy, class ForwardIterator, class Predicate, class T = iterator_traits<ForwardIterator>::value_type> void replace_if(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last, Predicate pred, const T& new_value); template<input_iterator I, sentinel_for<I> S, class Proj = identity, class T1 = projected_value_t<I, Proj>, class T2 = T1> requires indirectly_writable<I, const T2&> && indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T1*> constexpr I ranges::replace(I first, S last, const T1& old_value, const T2& new_value, Proj proj = {}); template<input_range R, class Proj = identity, class T1 = projected_value_t<iterator_t<R>, Proj>, class T2 = T1> requires indirectly_writable<iterator_t<R>, const T2&> && indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T1*> constexpr borrowed_iterator_t<R> ranges::replace(R&& r, const T1& old_value, const T2& new_value, Proj proj = {}); template<input_iterator I, sentinel_for<I> S, class Proj = identity, class T = projected_value_t<I, Proj>, indirect_unary_predicate<projected<I, Proj>> Pred> requires indirectly_writable<I, const T&> constexpr I ranges::replace_if(I first, S last, Pred pred, const T& new_value, Proj proj = {}); template<input_range R, class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires indirectly_writable<iterator_t<R>, const T&> constexpr borrowed_iterator_t<R> ranges::replace_if(R&& r, Pred pred, const T& new_value, Proj proj = {}); ```
Let E be
• bool(*i == old_value) for replace;
• bool(pred(*i)) for replace_if;
• bool(invoke(proj, *i) == old_value) for ranges​::​replace;
• bool(invoke(pred, invoke(proj, *i))) for ranges​::​replace_if.
Mandates: new_value is writable ([iterator.requirements.general]) to first.
Effects: Substitutes elements referred by the iterator i in the range [first, last) with new_value, when E is true.
Returns: last for the overloads in namespace ranges.
Complexity: Exactly last - first applications of the corresponding predicate and any projection.
```template<class InputIterator, class OutputIterator, class T = iterator_traits<OutputIterator>::value_type> constexpr OutputIterator replace_copy(InputIterator first, InputIterator last, OutputIterator result, const T& old_value, const T& new_value); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T = iterator_traits<ForwardIterator2>::value_type> ForwardIterator2 replace_copy(ExecutionPolicy&& exec, ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 result, const T& old_value, const T& new_value); template<class InputIterator, class OutputIterator, class Predicate, class T> constexpr OutputIterator replace_copy_if(InputIterator first, InputIterator last, OutputIterator result, Predicate pred, const T& new_value); template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class Predicate, class T> ForwardIterator2 replace_copy_if(ExecutionPolicy&& exec, ForwardIterator1 first, ForwardIterator1 last, ForwardIterator2 result, Predicate pred, const T& new_value); template<input_iterator I, sentinel_for<I> S, class O, class Proj = identity, class T1 = projected_value_t<I, Proj>, class T2 = iter_value_t<O>> requires indirectly_copyable<I, O> && indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T1*> && output_iterator<O, const T2&> constexpr ranges::replace_copy_result<I, O> ranges::replace_copy(I first, S last, O result, const T1& old_value, const T2& new_value, Proj proj = {}); template<input_range R, class O, class Proj = identity, class T1 = projected_value_t<iterator_t<R>, Proj>, class T2 = iter_value_t<O>> requires indirectly_copyable<iterator_t<R>, O> && indirect_binary_predicate<ranges::equal_to, projected<iterator_t<R>, Proj>, const T1*> && output_iterator<O, const T2&> constexpr ranges::replace_copy_result<borrowed_iterator_t<R>, O> ranges::replace_copy(R&& r, O result, const T1& old_value, const T2& new_value, Proj proj = {}); template<input_iterator I, sentinel_for<I> S,class O, class T = iter_value_t<O>, class Proj = identity, indirect_unary_predicate<projected<I, Proj>> Pred> requires indirectly_copyable<I, O> && output_iterator<O, const T&> constexpr ranges::replace_copy_if_result<I, O> ranges::replace_copy_if(I first, S last, O result, Pred pred, const T& new_value, Proj proj = {}); template<input_range R, class O, class T = iter_value_t<O>, class Proj = identity, indirect_unary_predicate<projected<iterator_t<R>, Proj>> Pred> requires indirectly_copyable<iterator_t<R>, O> && output_iterator<O, const T&> constexpr ranges::replace_copy_if_result<borrowed_iterator_t<R>, O> ranges::replace_copy_if(R&& r, O result, Pred pred, const T& new_value, Proj proj = {}); ```
Let E be
• bool(*(first + (i - result)) == old_value) for replace_copy;
• bool(pred(*(first + (i - result)))) for replace_copy_if;
• bool(invoke(proj, *(first + (i - result))) == old_value) for ranges​::​replace_copy;
• bool(invoke(pred, invoke(proj, *(first + (i - result))))) for ranges​::​replace_copy_if.
Mandates: The results of the expressions *first and new_value are writable ([iterator.requirements.general]) to result.
Preconditions: The ranges [first, last) and [result, result + (last - first)) do not overlap.
Effects: Assigns through every iterator i in the range [result, result + (last - first)) a new corresponding value
• new_value if E is true or
• *(first + (i - result)) otherwise.
Returns:
• result + (last - first) for the overloads in namespace std.
• {last, result + (last - first)} for the overloads in namespace ranges.
Complexity: Exactly last - first applications of the corresponding predicate and any projection.