Task.propagateValue

Gets the result of task as a #GValue, and transfers ownership of that value to the caller. As with [gio.task.Task.returnValue], this is a generic low-level method; [gio.task.Task.propagatePointer] and the like will usually be more useful for C code.

If the task resulted in an error, or was cancelled, then this will instead set error and return false.

Since this method transfers ownership of the return value (or error) to the caller, you may only call it once.