std::indirectly_writable
| Defined in header <iterator>
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| template< class Out, class T > concept indirectly_writable = |
(since C++20) | |
The concept indirectly_writable<Out, T> specifies the requirements for writing a value whose type and value category are encoded by T into an iterator 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
ebefore 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 object 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.