code: func (v *SelectionData) GetData() (data []byte) {
  	var length C.gint
  	c := C.gtk_selection_data_get_data_with_length(v.native(), &length)
  	sliceHeader := (*reflect.SliceHeader)(unsafe.Pointer(&data))
  	sliceHeader.Data = uintptr(unsafe.Pointer(c))
  	sliceHeader.Len = int(length)
  	sliceHeader.Cap = int(length)
  	return
  }
docs: // GetData is a wrapper around gtk_selection_data_get_data_with_length.
  // It returns a slice of the correct size with the selection's data.