pub type PFNGLVERTEXATTRIBL1UI64VARBPROC = Option<unsafe extern "C" fn(index: GLuint, v: *const GLuint64EXT)>;
enum PFNGLVERTEXATTRIBL1UI64VARBPROC { None, Some(unsafe extern "C" fn(_: u32, _: *const u64)), }
No value.
Some value of type T.
T