我正在阅读SFML游戏开发书籍，在完成第4章后，我有this code和这个编译器输出：
20:17:49: Starting: "/usr/bin/make"
g++ -o minimum aircraft.o command_queue.o entity.o game.o main.o player.o scene_node.o sprite_node.o world.o -L/usr/lib/i386-linux-gnu -lsfml-audio -lsfml-graphics -lsfml-network -lsfml-window -lsfml-system
player.o: In function `std::pair<APlayer::Action const, ACommand>::pair<APlayer::Action const&, 0u>(std::tuple<APlayer::Action const&>&, std::tuple<>&, std::_Index_tuple<0u>, std::_Index_tuple<>)':
/usr/include/c++/4.8/tuple:1088: undefined reference to `ACommand::ACommand()'
player.o: In function `std::pair<APlayer::Action const, ACommand>::pair<APlayer::Action&&, 0u>(std::tuple<APlayer::Action&&>&, std::tuple<>&, std::_Index_tuple<0u>, std::_Index_tuple<>)':
/usr/include/c++/4.8/tuple:1088: undefined reference to `ACommand::ACommand()'
collect2: error: ld returned 1 exit status
make: *** [minimum] Error 1
20:17:50: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project minimum (kit: Desktop)
When executing step 'Make'
20:17:50: Elapsed time: 00:01.
我的编译器是
g++ (Ubuntu 4.8.2-19ubuntu1) 4.8.2
对于一个混乱的问题抱歉，但我不知道发生了什么。如果有人帮忙，我会更清楚。