25 Iterators library [iterators]

25.3 Iterator requirements [iterator.requirements]

25.3.7 Common algorithm requirements [alg.req]

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

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The indirectly_copyable concept specifies the relationship between an indirectly_readable type and an 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>>;
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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, iter_value_t<In>&> && indirectly_writable<Out, const iter_value_t<In>&> && indirectly_writable<Out, iter_value_t<In>&&> && 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>>;
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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]).