no-throw-input-iterator, no-throw-forward-iterator, no-throw-sentinel-for, no-throw-input-range, no-throw-forward-range

template<class I>
concept no-throw-input-iterator = // exposition only
  std::input_iterator<I> &&
  std::is_lvalue_reference_v<std::iter_reference_t<I>> &&
  std::same_as<std::remove_cvref_t<std::iter_reference_t<I>>, std::iter_value_t<I>>;
(1) (since C++20)
template<class I>
concept no-throw-forward-iterator = // exposition only
  no-throw-input-iterator<I> &&
  std::forward_iterator<I> &&
  no-throw-sentinel-for<I, I>;
(2) (since C++20)
template<class S, class I>
concept no-throw-sentinel-for = std::sentinel_for<S, I>; // exposition only
(3) (since C++20)
template<class R>
concept no-throw-input-range = // exposition only
  ranges::range<R> &&
  no-throw-input-iterator<ranges::iterator_t<R>> &&
  no-throw-sentinel-for<ranges::sentinel_t<R>, ranges::iterator_t<R>>;
(4) (since C++20)
template<class R>
concept no-throw-forward-range = // exposition only
  no-throw-input-range<R> &&
(5) (since C++20)

These exposition-only concepts specify that no exceptions are thrown from operations required by algorithms on iterators, sentinels, and ranges.

1) The no-throw-input-iterator concept requires that dereferencing the iterator yields an lvalue, like contiguous_iterator and LegacyForwardIterator.

Semantic requirements

Like all standard concepts, every concept listed here is modeled only if all concepts it subsumes are modeled.

1) A type I models no-throw-input-iterator only if no exceptions are thrown from increment, copy construction, move construction, copy assignment, move assignment, or indirection through valid iterators.
3) Types S and I model no-throw-sentinel-for only if no exceptions are thrown from copy construction, move construction, copy assignment, move assignment, or comparisons between valid values of type I and S.
4) A type R models no-throw-input-range only if no exceptions are thrown from calls to ranges::begin and ranges::end on an object of type R.


These concepts allow some operations on iterators and sentinels to throw exceptions, e.g. operations on invalid values.

See also

specifies that a type is an input iterator, that is, its referenced values can be read and it can be both pre- and post-incremented
specifies that an input_iterator is a forward iterator, supporting equality comparison and multi-pass
specifies a type is a sentinel for an input_or_output_iterator type
specifies a range whose iterator type satisfies input_iterator
specifies a range whose iterator type satisfies forward_iterator

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