c++ - Is in-class enum forward declaration possible? -

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• c++ forward declaring class scoped enumeration 1 answer

i know in c++11 it's possible forward declare enum type (if storage type provided) e.g.

enum e : short; void foo(e e);  ....  enum e : short {     value_1,     value_2,     .... } 

but forward declare enum defined within class e.g.

enum foo::e : short; void foo(e e);  ....  class foo {     enum e : short     {         value_1,         value_2,     ....     } } 

is possible in c++11 ?

no, such forward declaration isn't possible. [decl.enum]/5 (bold emphasis mine):

if enum-key followed nested-name-specifier, the enum-specifier shall refer enumeration declared directly in class or namespace nested-name-specifier refers (i.e., neither inherited nor introduced using-declaration), , enum-specifier shall appear in namespace enclosing previous declaration.

(in case nested-name-specifier name of class followed ::.)
could, though, put enumeration outside , use opaque-enum-declaration.