pub type PFNGLPATHPARAMETERFNVPROC = Option<unsafe extern "C" fn(path: GLuint, pname: GLenum, value: GLfloat)>;
enum PFNGLPATHPARAMETERFNVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: f32)), }
No value.
Some value of type T.
T