pub type PFNGLBLENDCOLORPROC = Option<unsafe extern "C" fn(red: GLclampf, green: GLclampf, blue: GLclampf, alpha: GLclampf)>;
enum PFNGLBLENDCOLORPROC { None, Some(unsafe extern "C" fn(_: f32, _: f32, _: f32, _: f32)), }
No value.
Some value of type T.
T