Cannot Optionalize Class Getters

[bradenhs]

TypeScript Version: 2.2.1

Code

class Person {
  firstName: string;
  lastName: string;

  get fullName?() {
    return this.firstName + ' ' + this.lastName;
  }
}

Expected behavior:

Since fullName is optional the following should work:

const Me: Person = {
  firstName: 'Foo',
  lastName: 'Bar'
}

Actual behavior:

A syntax error occurs on this line get fullName?() {

I'm not sure if omitting the ability to optionalize getters was by design or not. If it was by design, I'd love to know the reasoning behind it.

[mhegazy]

A class is an implementation of a type. if you want to declare an optional property i suggest adding an interface Person:

interface Person {
   firstName: string;
   lastName: string;

  readonly fullName?;
}

[bradenhs]

Thanks! I'm aware that that's a possibility.

I suppose I just don't understand why the language would disallow marking getters as optional when everything else on a class can be marked as optional. It seems inconsistent. Is there a good reason for this inconsistency? Forgive me if I misunderstand, but the "A class is an implementation of a type" reasoning seems more like a how-the-compiler-is-implemented reason as opposed to a how-the-language-should-work reason. I'm interested in the later.

[mhegazy]

Accessors (getters/setters) are just properties. you can declare methods and properties as option. but you can not have an implementation to an optional property or a method.

[bradenhs]

Maybe I misunderstand. You can specify an implementation to an optional class method:

class Person {
  getName?() {
    return 'This is the name';
  }
}

There are no errors with that.

[Venryx]

@mhegazy Like bradenhs said, class methods can be made optional, as shown in this merged PR: #8625

class Bar {
    h?() {
        return 2;
    }
}

As can be seen, it's an optional method that also has a body/implementation specified.

That's the same thing we'd like for class getters/setters, like so:

class Bar {
    get h?() {
        return 2;
    }
}

However, this doesn't compile currently, which seems inconsistent when class methods work with it fine.

[RyanCavanaugh]

@mhegazy seems inconsistent to allow (bodied) optional methods but not getters. Thoughts?

[bradenhs]

If this suggestion is accepted would you guys take a PR for it? (I don't know much about the TypeScript code base but this doesn't seem like it would be a complicated task).

[bradenhs]

@ahejlsberg I saw that you implemented the ability to optionalize class properties in #8625. Is there a specific reason the ability to optionalize getters was omitted from that PR?