Scroll to navigation

std::projected(3) C++ Standard Libary std::projected(3)


std::projected - std::projected


Defined in header <iterator>
template< std::indirectly_readable I,

std::indirectly_regular_unary_invocable<I> Proj >
struct projected { (since
using value_type = std::remove_cvref_t<std::indirect_result_t<Proj&, (1) C++20)
std::indirect_result_t<Proj&, I> operator*() const; // not defined

template< std::weakly_incrementable I, class Proj >

struct incrementable_traits<std::projected<I, Proj>> { (2) (since
using difference_type = std::iter_difference_t<I>; C++20)


1) Class template projected combines an indirectly_readable type I and a callable
object type Proj into a new indirectly_readable type whose reference type is the
result of applying Proj to the std::iter_reference_t<I>.
2) This specialization of std::incrementable_traits makes std::projected<I, Proj> a
weakly_incrementable type when I is also a weakly_incrementable type.

projected is used only to constrain algorithms that accept callable objects and
projections, and hence its operator*() is not defined.

Template parameters

I - an indirectly readable type
Proj - projection applied to a dereferenced I