如何在继承树中处理静态工厂方法

Question

I have an inheritance hierarchy where objects can either be constructed normally with some values and some defaults supplied by the various constructors, or can be constructed from a serialized form with all values provided. I'd like to handle construction from the serialized form with static factory methods that I define on each class. Like so:

class A {
  constructor(x: number) {
     this.x = x;
  }

  static fromValues(v: {x: number}) {
    return new A(v.x);
  }
}

class B extends A {
  constructor(y: number) {
    super(0);
    this.y = y;
  }

  static fromValues(v: {x: number, y: number}) {
    // what goes here
  }
}

class C extends B {
  constructor(z: number) {
    super(0, 1);
    this.z = z;
  }

  static fromValues(v: {x: number, y: number, z: number}) {
    // what goes here
  }
}

The question is: how do I implement those methods? Also, preferably, they would offload some work to super class static factory methods.

Answer 1

This is a very opinionated topic (factories in JavaScript). The solution below is provided "in-kind" (written as your question) in order to provide a direct answer without opinion about other methods.

Note the typings are removed because of the limitation of the snippet tool.

Changes include adding default values in the constructor parameter list. That allows one to remove the hard coded values and optionally provide values for the sub-class constructors. Additionally, defaults are required in your static methods for the same reason.

This allows one to create individual objects or the entire hierarchy either via static factory method OR using the new keyword.

 class A { constructor(x = 0) { this.x = x; } static fromValues(v = {x:0}) { return new A(vx); } } class B extends A { constructor(y = 0, x) { super(x); this.y = y; } static fromValues(v = {y:0, x:0}) { return new B(vy, vx) } } class C extends B { constructor(z = 0, y, x) { super(y, x); this.z = z; } static fromValues(v = {z:0, y:0, x:0}) { return new C(vz, vy, vx); } } const a = A.fromValues({x: 3}); const b = B.fromValues({y: 2,x: 3}); const c = C.fromValues({z: 1,y: 2,x: 3}); const nv = C.fromValues(); console.log("A", a); console.log("B", b); console.log("C", c); console.log("No Values", nv);