Typescript3.1.3+泛型,类型赋值错误

class Farmer<A extends Animal<Farmer<A>>>
{
    public animal: A;
    constructor() {
        let a = new Animal(this);
        // ...
    }
}

class Animal<F extends Farmer<Animal<F>>>
{
    public farmer: F;
    constructor(f: F) {
        this.farmer = f;
    }
}

任何人都能解释为什么 Farmer 建造师(我经过的地方 this 论证 new Animal )上面的代码引发了这个错误?

TS2345: Argument of type 'this' is not assignable to parameter of type 'Farmer<Animal<this>>'.
 Type 'Farmer<A>' is not assignable to type 'Farmer<Animal<this>>'.
  Type 'A' is not assignable to type 'Animal<this>'.
   Type 'Animal<Farmer<A>>' is not assignable to type 'Animal<this>'.
    Type 'Farmer<A>' is not assignable to type 'this'.

class Farmer<A extends Animal<Farmer<A>>>
{
    public animal: A;
    constructor() {
        let a = new Animal(this as Farmer<A>); // works fine
    }
}

或者作为替代:

class Farmer<A extends Animal<Farmer<A>>>
{
    public animal: A;
    constructor() {
        let a = new Animal<Farmer<A>>(this); // works fine
    }
}

更奇怪的是:

class Farmer<A extends Animal<Farmer<A>>>
{
    // public animal: A; // removed this line
    constructor() {
        let a = new Animal(this); // now this one works fine too
    }
}

有人能解释一下发生了什么吗?

编辑

Animal 施工单位):

class Farmer<A extends Animal<Farmer<A>>>
{
    public animal: A;
    constructor() {
        let a = new Animal();
        a.farmer = this; // works fine
    }
}