19/10/26 08:16:08.08 kGqH5EJJ.net
>>604
g++だと、現状のままでok
vs2019は、friend宣言の対象が::AになっていてC2248
::Aをコメントアウトするとok
正しいのはg++
N4713 6.4.1. Unqualified name lookup (7.4)
Note: When looking for a prior declaration of a class or function
introduced by a friend declaration, scopes outside of the innermost
enclosing namespace scope are not considered; see 10.3.1.2.