25 Iterators library [iterators]

25.3 Iterator requirements [iterator.requirements]

25.3.4 Iterator concepts [iterator.concepts]

25.3.4.2 Concept indirectly_readable [iterator.concept.readable]

1
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Types that are indirectly readable by applying operator* model the indirectly_readable concept, including pointers, smart pointers, and iterators.
template<class In> concept indirectly-readable-impl = // exposition only requires(const In in) { typename iter_value_t<In>; typename iter_reference_t<In>; typename iter_rvalue_reference_t<In>; { *in } -> same_as<iter_reference_t<In>>; { ranges::iter_move(in) } -> same_as<iter_rvalue_reference_t<In>>; } && common_reference_with<iter_reference_t<In>&&, iter_value_t<In>&> && common_reference_with<iter_reference_t<In>&&, iter_rvalue_reference_t<In>&&> && common_reference_with<iter_rvalue_reference_t<In>&&, const iter_value_t<In>&>;
template<class In> concept indirectly_readable = indirectly-readable-impl<remove_cvref_t<In>>;
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Given a value i of type I, I models indirectly_readable only if the expression *i is equality-preserving.