13 Templates [temp]

13.7 Template declarations [temp.decls]

13.7.2 Class templates [temp.class] Static data members of class templates [temp.static]

A definition for a static data member or static data member template may be provided in a namespace scope enclosing the definition of the static member's class template.
[Example 1: template<class T> class X { static T s; }; template<class T> T X<T>::s = 0; struct limits { template<class T> static const T min; // declaration }; template<class T> const T limits::min = { }; // definition — end example]
An explicit specialization of a static data member declared as an array of unknown bound can have a different bound from its definition, if any.
[Example 2: template <class T> struct A { static int i[]; }; template <class T> int A<T>::i[4]; // 4 elements template <> int A<int>::i[] = { 1 }; // OK, 1 element — end example]