# Go interfaces are implicit: a type satisfies an interface by having the right…

By Saurabh Kumar · TIL note, Jul 19, 2026 · Tags: golang, architecture

Source: https://saurabh-kumar.com/til/1784462400/

Go interfaces are implicit: a type satisfies an interface by having the right methods, no `implements` keyword.
- Closest Python equivalent is `typing.Protocol` (structural subtyping, checked by mypy), but Go enforces it at compile time, not via a separate type checker.
- Sharp edge: a nil concrete pointer wrapped in an interface value is not `nil`. `var dog *Dog = nil; var s Speaker = dog` gives `s != nil` because the interface holds `(*Dog, nil)`, a typed pair. Bites hardest when returning `error` interfaces.
- Go proverb: "the bigger the interface, the weaker the abstraction." Keep them to 1-3 methods, define where consumed not where implemented.