Different behavior when declare property or method in a class about covariance

TypeScript Version: 4.1.2

Search Terms: In ts doc - type compatibility, it seems like not mentioned about this.

Code

class M1 {
  c: number = 1;
}

export class M2 extends M1 {
  a: number = 1;
}

type Func<M extends M1> = (m: M) => number;

interface IFunc<M extends M1> {
  func1?: Func<M>,
  func2: Func<M>,
}

class R1<M extends M1 = M1> implements IFunc<M> {
  // when delete this property, it will be no error.
  public func1 = (m: M) => {
    return m.c
  }

  public func2(m: M) {
    return m.c
  };
}

type IRConstructor<M extends M1, R extends R1<M>> = new () => R;

export class R2 extends R1<M2> {
}

type A = IRConstructor<M1, R1>;

let a1: A = R2; // error: Type 'typeof R2' is not assignable to type 'IRConstructor<M1, R1<M1>>'.

console.log(a1);

Expected behavior:

Should declare a property or a method in class has same behavior? I'm not sure...

Actually I want to know how can I make these code without error when I have to use functional property.

Actual behavior:

When you just decalre a method which is compatible with IFunc<M1>, it will be fine. But when you declare a functional property which is compatible with IFunc<M1>, it will be an error.

Playground Link:

Or, you can see playground

Related Issues:

Beginne mit der im Issue verlinkten TypeScript Playground-Reproduktion und dem im Issue referenzierten Abschnitt „Type Compatibility“ des Handbuchs. Vergleiche das gemeldete Verhalten der generischen Klasse für die Formen mit funktionaler Eigenschaft und Methode und stelle anschließend fest, ob der Unterschied beabsichtigt ist; abgeschlossen ist die Aufgabe, wenn ein erwartetes Verhalten festgelegt und die entsprechende Abdeckung im Compiler oder in der Dokumentation vorhanden ist.