[meta.type.synop] (and other) Repetitive 'inline constexpr'?

[jhunterkohler]

As can be seen in [meta.type.synop], there is constant use of inline constexpr. This is likely not limited just to this area of the text.

Example:

draft/source/utilities.tex

Lines 16155 to 16160 in 51c8df6

	template<class T>
	inline constexpr bool @\libglobal{is_void_v}@ = is_void<T>::value;
	template<class T>
	inline constexpr bool @\libglobal{is_null_pointer_v}@ = is_null_pointer<T>::value;
	template<class T>
	inline constexpr bool @\libglobal{is_integral_v}@ = is_integral<T>::value;

I had previously believed constexpr is implicitly inline for static data members, as specified in [dcl.constexpr]:

draft/source/declarations.tex

Lines 709 to 711 in 87ac40a

	A function or static data member
	declared with the \tcode{constexpr} or \tcode{consteval} specifier
	is implicitly an inline function or variable\iref{dcl.inline}.

Is inline constexpr used for clarity of the text?

I'll assume that this is not a mistake, so please let me know the reasoning. Alternatively, if it's not useful to have inline constexpr here, I can remove it and submit a pull request.

Thanks for your time!

[jwakely]

The [dcl.constexpr] text you've quoted only refers to functions and static data members. It doesn't apply to variable templates at namespace scope. Without the inline a variable such as is_void_v<int> would have internal linkage by default, so is_void_v<int> would be a different variable in every translation unit (and potentially cause ODR violations). Making it inline means there is a single variable that is the same in every translation unit.

[timsong-cpp]

Without the inline a variable such as is_void_v<int> would have internal linkage by default, so is_void_v<int> would be a different variable in every translation unit (and potentially cause ODR violations). Making it inline means there is a single variable that is the same in every translation unit.

We fixed that in CWG2387, but it came too late for most of the _v variable templates.

[jwakely]

Oh good, I didn't think that had actually got fixed yet. So the inline is redundant in C++20 (but not in C++17) and could be removed now.

[frederick-vs-ja]

Seems fixed by commit 9ac5555 (#4625 was not properly merged for some reason).