Clang C++20 Feature: P0732R2 - Class Types in Non-Type Template Parameters

[JVApen]

id: P0732R2
paper: https://wg21.link/p0732r2
partially implemented: status unknown

[llvmbot]

@llvm/issue-subscribers-c-20

[trueqbit]

I'd like to know the status of this feature.
cppreference's compiler support matrix lists "Class types in non-type template parameters" as partially implemented in clang 12. What does this mean exactly?

__cpp_nontype_template_args is still at version 201411L, however the 'string literal operator template' and constant evaluation of string literals works perfectly, see example on godbolt.

The reason I ask is that I am implementing a feature in the sqlite_orm library that relies heavily on "compile time" strings as template parameters.

[bolshakov-a]

I think it is fully implemented (in Clang 12) except some issues with MSVC compatibility (see https://reviews.llvm.org/D146386). Clang C++ status table has just a common cell for it and P1907R1. Even P1907R1 was almost fully implemented back in 2021 but reverted.

[nitnelave]

It doesn't seem quite fully implemented, for instance it's missing floats: https://godbolt.org/z/aa8n5qPYs

[bolshakov-a]

No, it's another feature: P1907R1.

[cs96and]

Seems that member functions of a class-type variadic class template must currently be declared inline. Moving them out of the function definition throws an error

nested name specifier 'Two<m...>::' for declaration does not refer into a class, class template or class template partial specialization

https://godbolt.org/z/o6aG4TT1P

[JVApen]

Status page indicates this is available from LLVM 12