pub type PFNGLCLEARCOLORIUIEXTPROC = Option<unsafe extern "C" fn(red: GLuint, green: GLuint, blue: GLuint, alpha: GLuint)>;
enum PFNGLCLEARCOLORIUIEXTPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: u32, _: u32)), }
No value.
Some value of type T.
T