pub type PFNGLPATHPARAMETERINVPROC = Option<unsafe extern "C" fn(path: GLuint, pname: GLenum, value: GLint)>;
enum PFNGLPATHPARAMETERINVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: i32)), }
No value.
Some value of type T.
T