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std::ranges::view_interface<D>::operator[] - cppreference.com

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template<ranges::random_access_range R = D> constexpr decltype(auto) operator[]( ranges::range_difference_t<R> n );

 (1) (since C++20)

template<ranges::random_access_range R = const D> constexpr decltype(auto) operator[]( ranges::range_difference_t<R> n ) const;

 (2) (since C++20)

The default implementation of operator[] member function obtains the element at the specified offset relative to the beginning iterator, reusing the operator[] of the iterator type.

1) Let derived be static_cast<D&>(*this). Equivalent to return ranges::begin(derived)[n];.

2) Same as (1), except that derived is static_cast<const D&>(*this).

Parameters

n - position of the element to return

Return value

The element at offset n relative to the beginning iterator.

Notes

In C++20, no type derived from ranges::view_interface in the standard library provides their own operator[] member function.

However, following derived types cannot use the default implementations, as they never satisfy random_access_range:

  • ranges::basic_istream_view
  • std::ranges::filter_view
  • ranges::join_view
  • ranges::lazy_split_view
  • ranges::split_view

The inherited operator[] member function is available for std::ranges::empty_view, but a call to it always results in undefined behavior.

Example