libc++ tests fail specifically due to this:

This implies that the destination range may fit the same element number as the source range contains. I thought only fitting the actually returned number of elements is enough.

They have:

      std::array<S, 4> in = {{{4, 2}, {1, 3}, {3, 4}, {3, 5}}};
      std::array<S, 2> out;
      auto ret = std::ranges::copy_if(in.begin(), in.end(), out.begin(), [](int i) { return i == 3; }, &S::val);

https://github.com/llvm/llvm-project/blob/79210feb2993ff9a79ef11f8a7016a527d4fcf22/libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/ranges.copy_if.pass.cpp#L160-L162

LLVM-139464 created.

Now that copycats are not enforced to have non-overlap, this looks even less useful.

I was very surprised to learn that copy_if / remove_copy / remove_copy_if / unique_copy require non-overlap as follows:

I think that standard shoould have a weaker precondition here. Just dest not in [first, last)

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

⛰️ ❌ 🏔️

I was very surprised to learn that copy_if / remove_copy / remove_copy_if / unique_copy require non-overlap as follows:

I think that standard shoould have a weaker precondition here. Just dest not in [first, last)

For the record, this is now LWG-4262