pub type PFNGLGETINTEGER64I_VPROC = Option<unsafe extern "C" fn(_: u32, _: u32, _: *mut i64)>;
enum PFNGLGETINTEGER64I_VPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: *mut i64)), }
No value.
Some value of type T.
T