From cppreference.com
template<ranges::random_access_rangeR=D>constexprdecltype(auto)operator[](ranges::range_difference_t<R>n); (1) (since C++20)template<ranges::random_access_rangeR=constD>constexprdecltype(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 returnranges::begin(derived)[n];.
2) Same as (1), except that derived is static_cast<constD&>(*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
in the standard library provides their own operator[] member function.
However, following derived types cannot use the default implementations, as they never satisfy
:
std::ranges::basic_istream_view
std::ranges::lazy_split_view
The inherited operator[] member function is available for
, but a call to it always results in undefined behavior.
Example