If you're following the distribution code, you're likely to have a variable named paddle that stores an instance of your paddle. If the ball collides with the paddle, detectCollision returns an instance of the same paddle (the one stored in paddle). You may think of the value that detect collision returns as an alias to the value stored in paddle. At this ...
You should use the second approach like other people suggested. In your code:
GObject object = detectCollision(window, ball)
if (strcmp(getType(object), "GRect") == 0)
You didn't state that the object is the bricks. Find a way to state that and you'll be fine. Good luck.