Should unions in JS be untagged? about jco

[esoterra]

I think what @Liamolucko might be suggesting is that variants be tagged, but unions be untagged in their JS representation, which is what I would personally vote for.

[alexcrichton]

I don't think that the current JS representation of variants is really all that great, and I think it'd be great to improve! I would ideally like to implement a representation trick where for:

variant url-like {
    literal(string),
    parsed(url),
}

struct url {
    // ... 
}

for that to be represented in JS as type UrlLike = string | URL. I believe we can do this because the url-like type has variants, each with a payload, each with a distinct JS class representing them, so cases can be determined by the class rather than using a discriminant. I think we'll still have to fall back to a discriminant for some cases, but I would hope that lots of cases could use a discriminant-less representation and delegate to type-checks for "checking the discriminant"

[guybedford]

Closing since unions have been removed.