pub type PFNGLGETNPIXELMAPUSVARBPROC = Option<unsafe extern "C" fn(map: GLenum, bufSize: GLsizei, values: *mut GLushort)>;
enum PFNGLGETNPIXELMAPUSVARBPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: *mut u16)), }
No value.
Some value of type T.
T