pub type PFNGLVERTEXATTRIBI3IEXTPROC = Option<unsafe extern "C" fn(index: GLuint, x: GLint, y: GLint, z: GLint)>;
enum PFNGLVERTEXATTRIBI3IEXTPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: i32, _: i32)), }
No value.
Some value of type T.
T