class Singleton { 
    static func get() {
        if( type._instance == null ) { 
            type._instance = new type(); 
        }
        return type._instance;
    } 
} 

/* 
Usage:

class SoundManager is Singleton { 
    func init() {
    
    } 
} 

var mgr = SoundManager.get();

//type is upvalue\preset value, like self
*/