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