constexpr auto size() requires ranges::forward_range<D> &&
std::sized_sentinel_for<ranges::sentinel_t<D>,
ranges::iterator_t<D>>;
| (1) | (since C++20) |
constexpr auto size() const requires ranges::forward_range<const D> &&
std::sized_sentinel_for<ranges::sentinel_t<const D>,
ranges::iterator_t<const D>>;
| (2) | (since C++20) |
The default implementation of size() member function obtains the size of the range by calculating the difference between the sentinel and the beginning iterator.
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.derived is static_cast<const D&>(*this).(none).
The difference between the sentinel and the beginning iterator of the value of the derived type, converted to its corresponding unsigned type.
Following derived types may use the default implementation of size():
Following types are derived from std::ranges::view_interface and do not declare their own size() member function, but they cannot use the default implementation, because their iterator and sentinel types never satisfy sized_sentinel_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 The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3646 | C++20 | the default implementations of size functions returned a signed type | they return unsigned type |
|
(C++17)(C++20) | returns the size of a container or array (function template) |
|
(C++20) | returns an integer equal to the size of a range (customization point object) |
|
(C++20) | returns a signed integer equal to the size of a range (customization point object) |
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