Question: Handling Optional Parameters & Named Arguments with Subclasses

[EotT123]

When using optional parameters and named arguments in a class hierarchy, is there a way to avoid duplicating default values in subclasses?

class A {
    A(int foo = 2, String bar = "bar"){ ... }
}

class B extends A {
    B(int foo = 2, String bar ="bar", long fooBar = 5L){
        super(foo, bar);
        ...
    }
}

In this example, the default values for foo and bar must be repeated in both class A and B.

[rsmckinney]

Looks like a regression from last round of changes. Thanks for reporting this.

[EotT123]

I'm not sure this is a regression, I'm wondering if this is even possible.
If you don't make the parameters of B optional (i.e. not duplicating the default values), the user is required to pass those values when constructing a B object.

So I would like to create B objects like this:

- new B(); // foo=2, bar=bar, fooBar=5L
- new B(bar:"test"); // foo=2, bar=test, fooBar=5L
- new B(bar:null); // foo=2, bar=null, fooBar=5L

But with a B constructor that looks like this:

B(int foo, String bar, long fooBar=5L){
    super(foo, bar);
    ...
}

But I don't think this is possible?

[rsmckinney]

Ah you're right about this not being a regression, my mistake.

This works with methods and not constructors because constructors are semi-static and can't override super class constructors. As a consequence they can't inherit default parameter values, at least not in the same way manifold implements the feature for virtual methods.

That said, it may be possible to establish a convention following the behavior of method overrides, albeit with more complicated code gen. But unless there is a pressing need for this feature, it'll probably have a low priority.

[EotT123]

I would be nice to have something like this, but there are probably more interesting things to work on. Since there is a workaround with some code duplication, you can consider this low priority.