pub type PFNGLVERTEXATTRIBI3UIPROC = Option<unsafe extern "C" fn(index: GLuint, v0: GLuint, v1: GLuint, v2: GLuint)>;
enum PFNGLVERTEXATTRIBI3UIPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: u32, _: u32)), }
No value.
Some value of type T.
T