NAME¶

std::output_iterator - std::output_iterator

Synopsis¶

Defined in header <iterator>
template <class I, class T>

concept output_iterator =
std::input_or_output_iterator<I> &&
std::indirectly_writable<I, T> && (since C++20)
requires(I i, T&& t) {
*i++ = std::forward<T>(t); // not required to be equality-preserving

};

The output_iterator concept is a refinement of input_or_output_iterator, adding the
requirement that it can be used to write values of type and value category encoded
by T (via indirectly_writable). equality_comparable is not required.

Semantic requirements

Let E be an expression such that decltype((E)) is T, and i be a dereferenceable
object of type I. output_iterator<I, T> is modeled only if all the concepts it
subsumes are modeled, and *i++ = E; has effects equivalent to *i = E; ++i;.

Equality preservation

An expression is equality preserving if it results in equal outputs given equal
inputs.

* The inputs to an expression consist of its operands.
* The outputs of an expression consist of its result and all operands modified by
the expression (if any).

In specification of standard concepts, operands are defined as the largest
subexpressions that include only:

* an id-expression, and
* invocations of std::move, std::forward, and std::declval.

The cv-qualification and value category of each operand is determined by assuming
that each template type parameter denotes a cv-unqualified complete non-array object
type.

Every expression required to be equality preserving is further required to be
stable: two evaluations of such an expression with the same input objects must have
equal outputs absent any explicit intervening modification of those input objects.

Notes¶

Unlike the LegacyOutputIterator requirements, the output_iterator concept does not
require that the iterator category tag be defined.

Algorithms on output iterators should be single pass.

See also¶

input_or_output_iterator specifies that objects of a type can be incremented and
(C++20) dereferenced
(concept)