pub type PFNGLVERTEXATTRIB2FARBPROC = Option<unsafe extern "C" fn(index: GLuint, x: GLfloat, y: GLfloat)>;
enum PFNGLVERTEXATTRIB2FARBPROC { None, Some(unsafe extern "C" fn(_: u32, _: f32, _: f32)), }
No value.
Some value of type T.
T