[a1o]

The implementation that exists for clang is fast but we will see how it goes with MSVC and GCC.

[gpderetta]

At least is a proof existence that it can be done.

[flohofwoe]

That doesn't mean much unfortunately, Clang had a fully working C99 designated initialization in C++ for many years, but the designated initialization that ended up in C++20 is only a butchered version of the full feature set despite Clang clearly demonstrating that it's possible to integrate the full C99 designated init feature set into C++.