Covariant builders - copy builder methods from superclass, with narrow return type

[blizznets]

In case I have, for example, super class for all my responses with such schema (Response.json):

{
  "$schema": "http://json-schema.org/draft-04/schema",
  "type": "object",
  "additionalProperties": false,
  "properties": {
    "error": {
      "type": "integer"
    }
  }
}

and some response that extends it (SomeResponse.json):

{
  "$schema": "http://json-schema.org/draft-04/schema",
  "type": "object",
  "additionalProperties": false,
  "extens": {
    "$ref": "Response.json"
  }
  "properties": {
    "whatEver": {
      "type": "string"
    }
  }
}

builder method "withError" will be generated for Response only.
So I've got compilation error when tried to do something like this:

new SomeResponse().withError(0).withWhatEver("somethnig");

But if withError override in each subclass - it will work.

public class SomeResponse extends Response{
    ...

    public SomeResponse withError(Integer error) {
        super.setError(error);
        return this;
    }

}

Is it possible to fix it?
Thanks a lot so helpfull tool!

[joelittlejohn]

This sounds possible. I'm interested to know if this is something people regularly run in to, as no-one has mentioned this in the past.

Rather than trying to find the setters, the simplest implementation would probably be:

• For each withXxx method in the superclass, introduce a withXxx method on the subclass
• The implementation in the subclass would:
  • call super.withXxx, passing the arg straight through
  • cast the returned value to narrow the type

[blizznets]

@joelittlejohn Thanks for reply.
Just one question: m.b. better just return "this", and ignore result of calling super.withXxx(), with out type casting?

[joelittlejohn]

Even better, I like it!

On 1 December 2015 at 09:48, blizznets notifications@github.com wrote:

@joelittlejohn https://github.com/joelittlejohn Thanks for reply.
Just one question: m.b. better just return "this", and ignore result of
calling super.withXxx(), with out type casting?

—
Reply to this email directly or view it on GitHub
#455 (comment)
.

[blizznets]

@joelittlejohn great! )
I'll waiting for new version with fix!

[joelittlejohn]

@blizznets I'm happy to accept a pull request if you want to fix this.

[blizznets]

@joelittlejohn ok )
Could you please assist me and help to find entry point to fixing it?

[joelittlejohn]

Which part are you having trouble with?

[joelittlejohn]

Closed by #458.