pub type PFNGLCREATETEXTURESPROC = Option<unsafe extern "C" fn(target: GLenum, n: GLsizei, textures: *mut GLuint)>;
enum PFNGLCREATETEXTURESPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: *mut u32)), }
No value.
Some value of type T.
T