Are static variables inlined by default inside templates in C++17?

Question

Are static variables inlined by default inside templates in C++17? Here's an example:

template<typename T> struct SomeClass {     static T test; };  struct SomeClass2 {     static constexpr int test = 9; }; 

Are those variables inlined or still need an out of line definition to be ODR used?

Answer 1

A static constexpr will implicitly also be inline, otherwise you will need to mark it as inline

template<typename T> struct SomeClass {     inline static T test; // Now inline };  struct SomeClass2 {     static constexpr int test = 9; // inline }; 

Cfr. from n4606 [depr.static_constexpr]

For compatibility with prior C++ International Standards, a constexpr static data member may be redundantly redeclared outside the class with no initializer. This usage is deprecated.

Example:

struct A {   static constexpr int n = 5; // definition (declaration in C++ 2014) }; const int A::n; // redundant declaration (definition in C++ 2014) 

and [dcl.constexpr] (Barry beat me to it)

A function or static data member declared with the constexpr specifier is implicitly an inline function or variable (7.1.6).