gistfile1.txt

class AAA{
    constructor(){
        console.log("aaa")
    }
}

class XXX{
}

class BBB extends XXX{
    constructor(){
        super()
        console.log("bbb")
    }
}

class CCC extends XXX{
    constructor(){
        super()
        console.log("ccc")
    }
}


class Hoge<A , B extends BBB|CCC>{
    constructor(public a : A , public b : B){
        console.log("XXXXX")
    }
}

class Fuga<B> extends Hoge<AAA , B>{}
class Fuga1<B> extends Fuga<B>{}
class Fuga2<B> extends Fuga<B>{}
class Fuga3<B> extends Fuga<B>{}
class Fuga4 extends Fuga<BBB>{}

interface Piyo{
    a : {new<B extends XXX>(p : AAA , q : B) :Fuga<B>}
}

class Bar implements Piyo{
    a = Fuga1
    constructor(){
        new this.a(new AAA() , new AAA()) // error? 
        new this.a(new AAA() , new BBB()) 
        new this.a(new AAA() , new CCC())
    }
}

new Bar()