typescript - typescript function argument inherits from

Question

I have a super class, such as

class SuperClassy {
}

Which has many other classes extending it:

class SubClassy extends SuperClassy {
}

class OtherSubClass extends SuperClassy {
}

etc.

I have functions for which I want to specify the argument must be in this group of derived classes.

I don't want to have to create a union type manually, I'd rather just declare that the argument in question must inherit from SuperClassy.

Something like:

function doStuff(c: InheritsFrom<SuperClassy>) {
}

such that this will compile:

doStuff(new SubClassy()) {
}

and this will not:

doStuff(4);

-- EDIT --

Here is an example where simply requiring parameter to be SuperClassy does not work:

class SuperClassy {
  id: string;
}

class SubClassy extends SuperClassy {
  x: number;
}

class OtherSubClass extends SuperClassy {
  y: number;
}

function doStuff(c: (c: SuperClassy) => (d: SuperClassy) => boolean) {
  return 'j';
}

doStuff((c: SubClassy) => {
  return (k: OtherSubClass) => {
    return c.id === k.id;
  }
});

Compiler throws this error:

Argument of type '(c: SubClassy) => (k: OtherSubClass) => boolean' is not assignable to parameter of type '(c: SuperClassy) => (d: SuperClassy) => boolean'.
  Types of parameters 'c' and 'c' are incompatible.
    Property 'x' is missing in type 'SuperClassy' but required in type 'SubClassy'.

标签： typescriptgenerics

Answer 1

How about using generics? (I added default values to the class definitions to suppress compiler errors.

class SuperClassy {
  id: string = "id";
}

class SubClassy extends SuperClassy {
  x: number = 0;
}

class OtherSubClass extends SuperClassy {
  y: number = 0;
}

function doStuff<T extends SuperClassy, U extends SuperClassy>(
  c: (c: T) => (d: U) => boolean
) {
  return "j";
}

doStuff((c: SubClassy) => {
  return (k: OtherSubClass) => {
    return c.id === k.id;
  };
});