std-ranges – Tarik Billa

C++20 ranges too many | operators?

August 9, 2023 by Tarik

TL;DR: In this case, the iterator type of the result of std::views::take is std::counted_iterator, which sometimes fails to model an iterator concept when it’s not expected to fail. This is LWG 3408 and is resolved by P2259. This involves some really complicated mechanism. Let T be the iterator type of values | std::views::filter(even) | std::views::transform(square), … Read more

Why must a std::ranges::filter_view object be non-const for querying its elements?

June 3, 2023 by Tarik

In order to provide the amortized constant time complexity required by range, filter_view::begin caches the result in *this. This modifies the internal state of *this and thus cannot be done in a const member function.