std::indirectly_readable - cppreference.com

From cppreference.com

Defined in header `<iterator>`
template< class In > concept __IndirectlyReadableImpl = requires(const In in) { typename std::iter_value_t<In>; typename std::iter_reference_t<In>; typename std::iter_rvalue_reference_t<In>; { *in } -> std::same_as<std::iter_reference_t<In>>; { ranges::iter_move(in) } -> std::same_as<std::iter_rvalue_reference_t<In>>; } && std::common_reference_with< std::iter_reference_t<In>&&, std::iter_value_t<In>& > && std::common_reference_with< std::iter_reference_t<In>&&, std::iter_rvalue_reference_t<In>&& > && std::common_reference_with< std::iter_rvalue_reference_t<In>&&, const std::iter_value_t<In>& >;		(exposition only*)
`template< class In > concept indirectly_readable = __IndirectlyReadableImpl<std::remove_cvref_t<In>>;`		(since C++20)

The concept indirectly_readable is modeled by types that are readable by applying operator*, such as pointers, smart pointers, and input iterators.

Semantic requirements

Given a value i of type I, I models indirectly_readable only if all concepts it subsumes are modeled and the expression *i is equality-preserving.

Equality preservation

Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).