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std::ranges...erface::size(3)  C++ Standard Libary std::ranges...erface::size(3)

NAME
     std::ranges::view_interface::size - std::ranges::view_interface::size

Synopsis
	constexpr auto size() requires ranges::forward_range<D> &&

	    std::sized_sentinel_for<ranges::sentinel_t<D>,		     (1)
     (since C++20)

				    ranges::iterator_t<D>>;
	constexpr auto size() const requires ranges::forward_range<const
	D> &&
									   (2)
     (since C++20)
	    std::sized_sentinel_for<ranges::sentinel_t<const D>,

				    ranges::iterator_t<const D>>;

	The default implementation of size() member function obtains the size of
     the range
	by calculating the difference between the sentinel and the beginning it-
     erator.

	1) Let derived be static_cast<D&>(*this). Equivalent to return
	/*to-unsigned-like*/(ranges::end(derived)  -   ranges::begin(derived));,
     where the
	exposition-only function template to-unsigned-like performs the explicit
     cast from
	the argument type to its corresponding unsigned type.
	2) Same as (1), except that derived is static_cast<const D&>(*this).

Parameters
	(none)

Return value
	The  difference  between  the sentinel and the beginning iterator of the
     value of the
	derived type, converted to its corresponding unsigned type.

Notes
	Following derived types may use the default implementation of size():

	  * std::ranges::drop_while_view

	Following types are derived from std::ranges::view_interface and do  not
     declare
	their own size() member function, but they cannot use the default imple-
     mentation,
	because  their	iterator  and  sentinel  types	never satisfy sized_sen-
     tinel_for:

	  * std::ranges::basic_istream_view
	  * std::ranges::filter_view
	  * std::ranges::join_view
	  * std::ranges::lazy_split_view
	  * std::ranges::split_view
	  * std::ranges::take_while_view

	Defect reports

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

	   DR	  Applied  to		 Behavior as published		    Cor-
     rect behavior
	LWG 3646 C++20	    the default implementations of size 	they re-
     turn unsigned
			    functions returned a signed type		type

See also
	size
	ssize	      returns the size of a container or array
	(C++17)       (function template)
	(C++20)
	ranges::size  returns an integer equal to the size of a range
	(C++20)       (customization point object)
	ranges::ssize returns a signed integer equal to the size of a range
	(C++20)       (customization point object)

http://cppreference.com 	   2024.06.10	   std::ranges...erface::size(3)
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