But you don't always have to return an error if something failed (say Hashmap lookup, strings.Index, or even just `if res1.IsValid()` without `err1` all togethe

But you don't always have to return an error if something failed (say Hashmap lookup, strings.Index, or even just `if res1.IsValid()` without `err1` all together), right? No, a real error type is strictly better than a success/failure bool, I think. For something like a hashmap lookup, “false” becomes “NotFound” (say) which is a lot clearer. And you don’t need the “true” at all -- in that case you just have the result of the lookup. In your “res1.IsValid” example, would you still be returning a separate error result, just not using it? If so, that seems a little dangerous -- how can the compiler verify that you’re correctly handling errors? If instead there’s no explicit error return, it seems like you’re not really using the language’s built-in error handling, and it could work equally well in either Go or Rust.