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); (since
   const_cast<const std::iter_reference_t<Out>&&>(*o) = 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 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 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 object it denotes
   is valid but unspecified.
  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
   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.