[josephg]

If all things are a trade-off, what would the trade-off of adding sum types be?

> All these things are a trade-off;

In some cases the trade-off is so one sided that its hardly worth the conversation. If everything is a trade-off, do you feel the same way about indenting your code? Or structured programming - aka using if/while blocks instead of gotos?

I think I'd confidently say that indented code makes everything simpler. And if I were given the choice, I think I'd choose structured programming every single time. I also don't often find myself questioning my daily choice to use high level languages rather than writing assembly directly. What else? Mmm... functions? I like those.

I feel the same way about sum types. They feel like an obviously good idea. Try as I might I can't think of any reason not to have them in a language like Go - except, as I already said - that they are another thing to learn when getting started. Having sum types and generics also makes it much easier for the type system to support optional types. And that makes it easier for a language to do away with Hoare's "billion dollar mistake".

If you disagree, I'd love to hear what you think the downsides are.

[arp242]

> If all things are a trade-off, what would the trade-off of adding sum types be?

Harder to write tooling for the language, bit harder to reason about code, possibly slower compiles (hard to claim this one for sure without a working implementation that has wide-spread use), harder to add features or change the language in the future, harder to work on (or implement a new) compiler.

None of these are insurmountable problems of course, and "Harder" means "harder relative to" rather than "hard". It's not clear to me anyway that sum times are a "slam dunk" type of feature. For example I've written a bunch of Go tooling over the years, and I really like that Go makes this fairly easy, partly due to the simple syntax. This is perhaps not something the "average developer does" or even a niche concern, but on the other hand: good tooling makes all the difference.

I'm not necessarily adding sum types to Go; details matter and it would partly depend on those.

Almost every single feature that has ever been added to any programming language was useful to add. I find many of Ruby's features useful, even some of the more esoteric ones, but that doesn't mean it was a good trade-off to add them.

[josephg]

> It's not clear to me anyway that sum times are a "slam dunk" type of feature.

They certainly are for me. I use them constantly in my two main languages - typescript and rust. Expressing similar ideas in go using iota and go's interfaces is far more awkward, inefficient and error prone.