pub type PFNGLGETVKPROCADDRNVPROC = Option<unsafe extern "C" fn(name: *const GLchar) -> GLVULKANPROCNV>;
enum PFNGLGETVKPROCADDRNVPROC { None, Some(unsafe extern "C" fn(_: *const i8) -> Option<unsafe extern "C" fn()>), }
No value.
Some value of type T.
T