cppdraft_translate/cppdraft/temp/mem/class.md

[temp.mem.class]

13 Templates [temp]

13.7 Template declarations [temp.decls]

13.7.2 Class templates [temp.class]

13.7.2.4 Member classes of class templates [temp.mem.class]

1

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A member class of a class template may be defined outside the class template definition in which it is declared.

[Note 1:

The member class must be defined before its first use that requires an instantiation ([temp.inst]).

For example,template struct A {class B;}; A::B* b1; // OK, requires A to be defined but not A​::​Btemplate class A::B { }; A::B b2; // OK, requires A​::​B to be defined

— end note]