pub type PFNGLWINDOWRECTANGLESEXTPROC = Option<unsafe extern "C" fn(mode: GLenum, count: GLsizei, box_: *const GLint)>;
enum PFNGLWINDOWRECTANGLESEXTPROC { None, Some(unsafe extern "C" fn(_: u32, _: i32, _: *const i32)), }
No value.
Some value of type T.
T