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std::ranges::subrange<I,S,K>::subrange

subrange() requires std::default_initializable<I> = default;
 (1) (since C++20) 
constexpr subrange( /*convertible-to-non-slicing*/<I> auto i, S s )
  requires (!/*store-size*/);
 (2) (since C++20) 
constexpr subrange( /*convertible-to-non-slicing*/<I> auto i, S s,
                    /*make-unsigned-like-t*/<std::iter_difference_t<I>> n )
  requires (K == ranges::subrange_kind::sized);
 (3) (since C++20) 
template< /*different-from*/<subrange> R >
  requires ranges::borrowed_range<R> &&
           /*convertible-to-non-slicing*/<ranges::iterator_t<R>, I> &&
           std::convertible_to<ranges::sentinel_t<R>, S>
constexpr subrange( R&& r ) requires (!/*store-size*/ || ranges::sized_range<R>);
 (4) (since C++20) 
template< ranges::borrowed_range R>
  requires /*convertible-to-non-slicing*/<ranges::iterator_t<R>, I> &&
           std::convertible_to<ranges::sentinel_t<R>, S>
  constexpr subrange( R&& r, /*make-unsigned-like-t*/<std::iter_difference_t<I>> n )
    requires (K == ranges::subrange_kind::sized)
      : subrange{ranges::begin(r), ranges::end(r), n}
  {}
 (5) (since C++20)

Constructs a subrange.

If K == ranges::subrange_kind::sized && !std::sized_sentinel_for<S, I>, the size of the range is stored into the subrange, as if stored by a member subobject of type /*make-unsigned-like-t*/<std::iter_difference_t<I>>, where make-unsigned-like-t is an exposition-only alias template that maps each integer-like type to its corresponding unsigned version. Otherwise, the size is not stored. The constant store-size is true if the size is stored, false otherwise.

1) Default constructor. Value-initializes the stored iterator and sentinel as if by default member initializers = I() and = S(), respectively. If the size is stored, it is initialized with ​0​ as if by the default member initializer = 0.
2) Constructs a subrange from an iterator-sentinel pair. Initializes the stored iterator and sentinel with std::move(i) and s respectively. The behavior is undefined if [i, s) is not a valid range.
3) Constructs a subrange from an iterator-sentinel pair and a size hint. Initializes the stored iterator and sentinel with std::move(i) and s respectively. If the size is stored, it is initialized with n. The behavior is undefined if [i, s) is not a valid range, or n is not equal to ranges::distance(i, s) explicitly converted to its type.
4) Constructs a subrange from a range. Equivalent to subrange(r, static_cast</*make-unsigned-like-t*/<std::iter_difference_t<I>>>(ranges::size(r))) if the size is stored. Otherwise, equivalent to subrange(ranges::begin(r), ranges::end(r)).
5) Constructs a subrange from a range and a size hint. The behavior is undefined if n is not equal to ranges::distance(ranges::begin(r), ranges::end(r)) explicitly converted to its type.

The exposition only concept different-from is modeled by types T and U if and only if std::decay_t<T> and std::decay_t<U> are different types.

The exposition only concept convertible-to-non-slicing is satisfied or modeled by From and To if and only if std::convertible_to<From, To> is satisfied or modeled respectively, and ​any of following conditions is satisfied:

Parameters

i - iterator that denotes the beginning of the range
s - sentinel that denotes the end of the range
r - range
n - size hint, must be equal to the size of the range

Notes

The exposition-only concept convertible-to-non-slicing forbids the conversion from the pointer to derived class to the pointer to base class.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3470 C++20 convertible-to-non-slicing rejected some valid qualification conversions made accepted
P2393R1 C++20 implicit conversion to an integer-class type might be invalid made explicit

Example

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