pub type PFNGLISVERTEXATTRIBENABLEDAPPLEPROC = Option<unsafe extern "C" fn(index: GLuint, pname: GLenum) -> GLboolean>;
enum PFNGLISVERTEXATTRIBENABLEDAPPLEPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32) -> u8), }
No value.
Some value of type T.
T