pub type PFNGLGETVARIANTFLOATVEXTPROC = Option<unsafe extern "C" fn(id: GLuint, value: GLenum, data: *mut GLfloat)>;
enum PFNGLGETVARIANTFLOATVEXTPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: *mut f32)), }
No value.
Some value of type T.
T