pub type PFNGLPROGRAMUNIFORM2DPROC = Option<unsafe extern "C" fn(program: GLuint, location: GLint, v0: GLdouble, v1: GLdouble)>;
pub enum PFNGLPROGRAMUNIFORM2DPROC { None, Some(unsafe extern "C" fn(u32, i32, f64, f64)), }
No value.
Some value of type T.
T