pub type PFNGLVERTEXATTRIBI2UIEXTPROC = Option<unsafe extern "C" fn(index: GLuint, x: GLuint, y: GLuint)>;
enum PFNGLVERTEXATTRIBI2UIEXTPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: u32)), }
No value.
Some value of type T.
T