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std::indirectly_writable(3) C++ Standard Libary std::indirectly_writable(3) NAME std::indirectly_writable - std::indirectly_writable Synopsis Defined in header <iterator> template< class Out, class T > concept indirectly_writable = requires(Out&& o, T&& t) { *o = std::forward<T>(t); *std::forward<Out>(o) = std::forward<T>(t); const_cast<const std::iter_reference_t<Out>&&>(*o) = (since std::forward<T>(t); C++20) const_cast<const std::iter_reference_t<Out>&&>(*std::forward<Out>(o)) = std::forward<T>(t); }; /* none of the four expressions above are required to be equality-preserving */ The concept indirectly_writable<Out, T> specifies the requirements for writing a value whose type and value category are encoded by T into an itera- tor Out's referenced object. Semantic requirements Let e be an expression such that decltype((e)) is T, and o be a dereferenceable object of type Out, then indirectly_writable<Out, T> is modeled only if: * If std::indirectly_readable<Out> is modeled and std::iter_value_t<Out> is the same type as std::decay_t<T>, then *o after any above assignment is equal to the value of e before the assignment. o is not required to be dereferenceable after evaluating any of the assignment expressions above. If e is an xvalue, the resulting state of the ob- ject it denotes is valid but unspecified. Equality preservation Expressions declared in requires expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise). Notes The only valid use of operator* is on the left side of an assignment expression. Assignment through the same value of an indirectly writable type may happen only once. The required expressions with const_cast prevent indirectly_readable objects with prvalue reference types from satisfying the syntactic requirements of indirectly_writable by accident, while permitting proxy references to continue to work as long as their constness is shallow. See Ranges TS issue 381. http://cppreference.com 2024.06.10 std::indirectly_writable(3)
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