namespace CombiningInterfaces { interface ISpeaker { playSound ( ) : void ; } interface IVolumeControl { volumeUp ( ) : void ; volumeDown ( ) : void ; } interface ISpeakerWithVolumeControl extends ISpeaker , IVolumeControl { } class MySpeaker implements ISpeakerWithVolumeControl { playSound ( ) { } volumeUp ( ) { } volumeDown ( ) { } } class MusicPlayer { speaker : ISpeakerWithVolumeControl ; constructor ( speaker ) { this . speaker = speaker ; } } }