What is executed before the function marked with the @main annotation?

In Swift, the @main annotation indicates the entry point of the application, replacing the traditional main() function. Before executing the function or structure marked with @main, the Swift runtime environment is initialized and necessary system resources are loaded. Specifically, the application environment is configured, static variables are loaded, global states are initialized, and preparations are made to run the main application code.

For example, in an iOS application, a @main struct is launched after the system has created the process and set up basic system services, then the code inside @main is called to start the application.