Lib.rs

AppInstance

在应用程序中任意时刻一次性实例化，应用程序退出时将销毁

pub struct Application { main_window: Window }

impl Application
{
	// Instantiated an Application once
	AppInstance!(pub static instance: Application = Application::new());
	fn new() -> Self { ... }
}
// Application::main_window::drop is going to be called at exit

lib.rs:

懒加载静态，当应用程序正常退出时释放值