pub type PFNGLVERTEXATTRIBS4UBVNVPROC = Option<unsafe extern "C" fn(index: GLuint, n: GLsizei, v: *const GLubyte)>;
enum PFNGLVERTEXATTRIBS4UBVNVPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: *const u8)), }
No value.
Some value of type T.
T