function minusTwo({ set, get }) {
  return {
    set(v) {
      set.call(this, v - 2)
    },
    init(v) {
      return v - 2;
    }
  }	
}

function timesFour({ set, get }) {
  return {
    set(v) {
      set.call(this, v * 4)
    },
    init(v) {
      return v * 4;
    }
  }	
}

class Foo {
  @minusTwo @timesFour accessor bar = 5;
}

const foo = new Foo();
console.log({ init: foo.bar });

foo.bar = 5;	
console.log({ set: foo.bar });