Module 2 · Exercise 1 · ~25 min · Real Go code

Refactor a Non-Idiomatic File

A working but ugly Go file. Nine specific issues — each maps to a Module 2 lesson concept. Make it idiomatic; the tests must keep passing.

cd module-02-idiomatic-go/exercises/exercise-01-refactor
go test -v ./...

The nine smells

1. Package name uses underscore + util suffix.
2. Type name SubmitterClass stutters and uses Java-isms.
3. Method DoSubmit has a redundant prefix.
4. Receiver name this.
5. String-concatenated errors instead of fmt.Errorf with %w.
6. Returning a typed nil pointer as an interface (the trap from M1).
7. ErrorTimeout sentinel naming.
8. Missing doc comments on exported identifiers.
9. Exported mutable config field that should be hidden.

What "idiomatic" means here

This is not aesthetic. Each smell maps to a real failure mode:

• The nil-interface trap is a runtime bug waiting to happen.
• Bad receiver names confuse readers — s is universal in Go for any struct method receiver.
• Strings instead of %w means callers can't errors.Is anything.
• Public mutable fields create undocumented coupling between caller and library.

When green

Skim the diff. Imagine you're reviewing it. Would you approve? If yes, mark complete and move to Exercise 2 (writing your own table-driven test suite).