[LLVMbugs] [Bug 13517] Static constexpr definitions used inside template

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Jan 8 14:55:33 PST 2013


Richard Smith <richard-llvm at metafoo.co.uk> changed:

           What    |Removed                     |Added
             Status|NEW                         |RESOLVED
         Resolution|                            |INVALID

--- Comment #5 from Richard Smith <richard-llvm at metafoo.co.uk> 2013-01-08 16:55:33 CST ---
(In reply to comment #0)
> [...] when I make the class A, a template like this:
> Clang crashes

I cannot reproduce this with Clang trunk; I assume it has been fixed.

> if I change the definition line for F to this:
> Then clang produces this error:
> error: redefinition of 'F' with a different type
> constexpr typename std::remove_const<decltype(A<X>::F)>::type A<X>::F;
>                                                                     ^
> note: previous definition is here
>     static constexpr auto F = L();
>                           ^

This error is correct. 'constexpr' and 'auto' are red herrings here. Reduced

template<class X> struct A { static int F; };
template<class X> decltype(A<X>::F) A<X>::F;

Per C++11 [temp.type]p2, "If an expression e involves a template parameter,
decltype(e) denotes a unique dependent type." Therefore the type of A<X>::F
does not match the type in the template.

> Also, does C++ require the definition outside of the class? It would be nicer
> when using constexpr and auto, just to have the the static member defined at
> the point of declaration.(like it is for integers), but perhaps that is not
> conformant with C++11.

static const integral members work just like static constexpr members in this
regard. In either case, you must provide a definition outside the class if the
data member is odr-used (more-or-less, if its address is used, not just its

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