pub type PFNGLGETVERTEXARRAYIVPROC = Option<unsafe extern "C" fn(vaobj: GLuint, pname: GLenum, param: *mut GLint)>;
enum PFNGLGETVERTEXARRAYIVPROC { None, Some(unsafe extern "C" fn(_: u32, _: u32, _: *mut i32)), }
No value.
Some value of type T.
T