Google Maps fill full screen. How to fill it to half screen?

I use the next code:

var camera = GMSCameraPosition.cameraWithLatitude(40.378259,
        longitude: 49.875059, zoom: 16)
    var mapView = GMSMapView.mapWithFrame(CGRectZero, camera: camera)
    mapView.myLocationEnabled = true
    self.view = mapView

    var marker = GMSMarker()
    marker.position = CLLocationCoordinate2DMake(40.378259, 49.875059)
    marker.map = mapView

and I use constraints, but it doesn't helps me. My map fills full screen, even if I do the next:

var mapView = GMSMapView.mapWithFrame(CGRectMake(0, 0, 100, 100), camera: camera)

Why it doesn't work? How can I fix it? I connect it by Podfile