Dependency Injection in Go Without a Framework

How to do DI in Go without Wire or Dig. Interfaces, constructors, wiring in main.go — and why a DI framework is often the wrong answer to a real design problem.

martedì 2 giugno 2026 New tab

982 words~4 min read

The unit test took 4 seconds. Not because the logic was complex — because the service sent a real email on every call. The constructor instantiated the SMTP client internally. There was no way to replace it in tests without modifying production code.

That's the hidden dependency. It's invisible in the function signature, it doesn't crash at runtime — but it makes code impossible to test cleanly and impossible to evolve without side effects.

The hidden dependency

Here's what it looks like:

type OrderService struct {