pub type PFNGLBEGINQUERYINDEXEDPROC = Option<unsafe extern "C" fn(target: GLenum, index: GLuint, id: GLuint)>;
enum PFNGLBEGINQUERYINDEXEDPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: u32)), }
No value.
Some value of type T.
T