pub type PFNGLDRAWTRANSFORMFEEDBACKSTREAMPROC = Option<unsafe extern "C" fn(mode: GLenum, id: GLuint, stream: GLuint)>;
enum PFNGLDRAWTRANSFORMFEEDBACKSTREAMPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: u32)), }
No value.
Some value of type T.
T