[saghm]

Slight nit: Rust does have an `Any` type[0] (and has since at least 1.0). Unlike Go's `interface{}`/`Any` type though, it's actually type-safe; the only way to get a value from it is to try to downcast into a concrete type, which returns an Option and will always be `None` if it doesn't match the type.

[0]: https://doc.rust-lang.org/std/any/trait.Any.html

[jerf]

That's generally how interface{} works in Go too. In local idioms, but the same effect. Only valid operations are permitted.

If you continue to disagree with me, please be specific about what operation Go permits on interface{} values that you consider type-unsafe.

[saghm]

The trailing suffix cast (not sure the actual name, but `x.(string)` and the like) are not type safe. Yes, it's not required to be able to try to deal with an empty interface type, but it's there, and it will always compile fine and allow code afterwards to freely assume the cast succeeded without any errors.

I imagine the rebuttal to this is that you could always just manually `unwrap` the `Option` that is returned by the downcast methods in Rust, but I pretty strongly feel that adding explicit syntax for this type of unsafe cast normalizes it to an extent that having an `unwrap` method on a generic Option type doesn't remotely approach. It would be quite a stretch to argue that having the `unwrap` method on Option is explicitly a endorsement on unwrapping on the downcast methods given that Option is used for far more than just that (and especially given the huge amount of stigma that using `unwrap` gets in the community, which is mostly fair but sometimes goes a little overboard). On the other hand, having specific syntax that is used for unsafe casts and nothing else is a pretty explicit argument that it should be done sometimes, or else it wouldn't be in the language at all. Go could pretty easily have gone the route they did with map lookups and had the unsafe casts return two values, the latter of which is a boolean indicating success or failure (and in the cast of `false` being returned, the former value would just be the zero value for the output type), and the fact that this wasn't done means that ergonomics was prioritized over safety.

[jerf]

"Yes, it's not required to be able to try to deal with an empty interface type, but it's there, and it will always compile fine and allow code afterwards to freely assume the cast succeeded without any errors."

That is incorrect. It issues a runtime panic, which is the same as the syntax for Rust that will do the same thing. Or you can use the "x, isX = y.(SomeType)" syntax and it will tell you whether it matches or not.

It's the exact same functionality just spelled differently, but there is no scenario where you have an int but you call it a string and the code simply proceeds along and does whatever.

"unsafe casts return two values"

It does do that! It's done it since the beginning. It's not a cast, though. It's a "type assertion". It can't convert. Go only has casting for safe conversions... well, things most programmers consider safe. I don't consider int -> byte "safe" but I am in the minority on that.

You need to stop talking about Go. You don't know it. There's nothing wrong with not knowing it, but you shouldn't combine that with trying to explain it to people. It isn't as crazy as you think. It is definitely type-safe. The "type safe" that it is is less rich and complex than Rust or Haskell, but it is type safe within its type system, subject to the usual "unsafe" caveat. If it weren't, it would never had needed generics... it would be a dynamic language and they build generics in so deep they aren't even "generics", they're just how the language works at all. The whole reason Go needs generics is precisely that it isn't type-unsafe.

[saghm]

> That is incorrect. It issues a runtime panic, which is the same as the syntax for Rust that will do the same thing.

As I said before, having explicit syntax for it is a very different thing than having a method for it on a generic type that isn't specific to it

> It does do that! It's done it since the beginning

That's good! Still isn't required though, and having a safe way to do something doesn't mean that the unsafe way doesn't exist

> It's not a cast, though. It's a "type assertion". It can't convert.

Okay? It still lets you get errors due to the type system not preventing them

> It is definitely type-safe. The "type safe" that it is is less rich and complex than Rust or Haskell, but it is type safe within its type system

I agree that type safety is a spectrum, and very few languiages are fully type safe. I probably should have been more clear that I wasn't saying that Go wasn't 100% unsafe, but I thought it would be obvious I wasn't saying that. Clearly that's not the case.

> If it weren't, it would never had needed generics... it would be a dynamic language and they build generics in so deep they aren't even "generics", they're just how the language works at all. The whole reason Go needs generics is precisely that it isn't type-unsafe.

I'm not sure what this means; pretty much every statically typed language gets benefits from generics, and they're clearly not all equally type safe, so I don't know what this is supposed to convince me of.

> You need to stop talking about Go. You don't know it.

I don't know everything about Go, that's true. Go doesn't have a special definition of type safety though, and recognizing places where it isn't type safe doesn't require complete knowledge of the entire language.

[feffe]

They are called type assertions, I believe they are type safe, albeit at runtime. It will panic if the assertion is incorrect.