Error: invalid use of incomplete type 'class Move' / undefined reference to Move::NONE-CodePudding

Home > Software design > Error: invalid use of incomplete type 'class Move' / undefined reference to Move::NONE

Error: invalid use of incomplete type 'class Move' / undefined reference to Move::NONE

Time：07-09

Please, I don't know why this simple code is rejected.

It give me 2 compilation errors. Help me please.