pub type PFNGLCLEARBUFFERFVPROC = Option<unsafe extern "C" fn(buffer: GLenum, drawBuffer: GLint, value: *const GLfloat)>;
enum PFNGLCLEARBUFFERFVPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: *const f32)), }
No value.
Some value of type T.
T