type Constructor<T> = new (...args: any[]) => T;

export class Singleton {
    private static instances = new Map<Constructor<Singleton>, Singleton>();
    public static getInstance<T extends Singleton>(
        this: Constructor<T>
    ): T {
        let instance = Singleton.instances.get(this);
        if (!instance) {
            instance = new this();
            Singleton.instances.set(this, instance);
        }
        return instance as T;
    }
}