wxWidgets源代码中程序对象实例化有如下宏：
#define wxIMPLEMENT_APP_NO_MAIN(appname)                                    \
appname& wxGetApp() { return *static_cast<appname*>(wxApp::GetInstance()); }    \
wxAppConsole *wxCreateApp()                                             \
{                                                                       \
wxAppConsole::CheckBuildOptions(WX_BUILD_OPTIONS_SIGNATURE,         \
“your program”);                    \
return new appname;                                                 \
}
其中appname为自定义类，wxAppConsole为基类
指针函数不应该返回一个类指针么？ 为什么此处返回一个子类实例？