I'm saying Go has a weak type system. This was apparently an intentional choice by the authors. Go doesn't even have sum types, which are an extremely basic, foundational feature of type systems. Even C had an equivalent in its union types.
"Weak type system" means that there are many restrictions on what constitutes a valid program that can't be expressed in Go, that can be expressed in languages with stronger type systems, like Rust, Haskell, or even Java and C#.