pub type PFNGLUNIFORM2DVPROC = Option<unsafe extern "C" fn(location: GLint, count: GLsizei, value: *const GLdouble)>;
enum PFNGLUNIFORM2DVPROC { None, Some(unsafe extern "C" fn(_: i32, _: i32, _: *const f64)), }
No value.
Some value of type T.
T