23 Iterators library [iterators]

23.3 Iterator requirements [iterator.requirements]

23.3.7 Common algorithm requirements [alg.req]

23.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]

The indirectly_­copyable concept specifies the relationship between a indirectly_­readable type and a indirectly_­writable type between which values may be copied.
template<class In, class Out>
  concept indirectly_copyable =
    indirectly_readable<In> &&
    indirectly_writable<Out, iter_reference_t<In>>;
The indirectly_­copyable_­storable concept augments indirectly_­copyable with additional requirements enabling the transfer to be performed through an intermediate object of the indirectly_­readable type's value type.
It also requires the capability to make copies of values.
template<class In, class Out>
  concept indirectly_copyable_storable =
    indirectly_copyable<In, Out> &&
    indirectly_writable<Out, const iter_value_t<In>&> &&
    copyable<iter_value_t<In>> &&
    constructible_from<iter_value_t<In>, iter_reference_t<In>> &&
    assignable_from<iter_value_t<In>&, iter_reference_t<In>>;
Let i be a dereferenceable value of type In.
In and Out model indirectly_­copyable_­storable<In, Out> only if after the initialization of the object obj in
iter_value_t<In> obj(*i);
obj is equal to the value previously denoted by *i.
If iter_­reference_­t<In> is an rvalue reference type, the resulting state of the value denoted by *i is valid but unspecified ([lib.types.movedfrom]).