> Tagged structs are not meaningfully less type safe than interfaces.

Of course they are. What if you read from or write to the wrong field?

> Use an enum for the tag

Your example has one contained type per variant. In Rust it is common to have an enum like

    enum Foo {
      Variant1(String, u8, Vec<u8>),
      Variant2(u8),
      Variant3(String),
      Variant4(f32),
      Variant6(f32)
      Variant5(bool, bool, String)
   }

Naming tags for something like this would be hard. Some of the fields would be shared between variants. Some would not.

> Of course they are. What if you read from or write to the wrong field?

This falls under the rubric of "not meaningfully less type safe". This data structure is central in a large project of mine, and I have maybe 3 places where I switch on the type flag. I'm not proposing this as a general purpose replacement for interfaces, only a useful way to abstract over a few known types when you can't afford all of the allocs.

> Your example has one contained type per variant. In Rust it is common to have an enum like enum Foo { Variant1(String, u8, Vec<u8>), Variant2(u8), Variant3(String), Variant4(f32), Variant6(f32) Variant5(bool, bool, String) }

I agree. I don't propose this as a general purpose replacement for Rust's enums.

> I agree. I don't propose this as a general purpose replacement for Rust's enums.

Yeah, that's the thing, Rust enums used this way are very powerful. I'm fine with making tagged structy things in cases like the one mentioned, I feel Go can handle that. I'm missing out on all the useful stuff I can do with proper algebraic datatypes.