Discriminated Unions pattern support

[doblak]

I'd find it useful to be able to provide 'kind' string literal (see discriminated unions: https://www.typescriptlang.org/docs/handbook/advanced-types.html)

Example:

interface SquareDto {
    kind: "SQUARE";
    size: number;
}
interface CircleDto {
    kind: "CIRCLE";
    radius: number;
}

It would be possible to define public final String kind = "CIRCLE"; or maybe even public final ShapeKind kind = ShapeKind.CIRCLE; on dto.

Currently that gets emitted as kind: string; or kind: ShapeKind in typescript.

What do you think?

Thanks

[doblak]

Just noticed #26, I'll look into it, it might suffice.

[vojtechhabarta]

@doblak if you are using Jackson 2 have a look also at support for tagged unions (discriminated unions) #81.

[doblak]

That works great. I'd prefer if kind property was emitted to the actual class having @JsonTypeName annotation (not the first non-interface/abstract class), but ... it's probably good enough.

In case you wonder what's the use case ... with immutables the immutable implementation gets appended the kind field.

Relevant code:
Jackson2Parser.java:90

/.../ else if (!sourceClass.type.isInterface() && !Modifier.isAbstract /.../

e.g. if we only add immutable implementation for circle:

interface SquareDto {
    kind: "SQUARE";
    size: number;
}
interface CircleDto {
    radius: number;
}
interface ImmutableCircleDto extends CircleDto {
    kind: "CIRCLE";
}

[vojtechhabarta]

Great to hear that it works for you.

Actually I don't remember all details why I implemented it this way. It was relatively complicated to describe Jackson's kind of dynamic behavior with TypeScript static typing and I am happy that it works for most cases 😉