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