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Interfaces Everywhere vs Interfaces Where Needed: A Go Architecture Experiment

A hands-on Go experiment comparing interfaces-everywhere against interfaces-where-needed — the results might change how you code.

6 min readJul 30, 2026

Somewhere along the way, a lot of us learned a rule that sounded wise: “program to an interface, not an implementation.” Fair enough advice — until it turns into a habit of slapping an interface on every single struct in your codebase, whether it needs one or not. Suddenly every service, every repository, every tiny helper has a matching interface definition sitting right above it, most of which are implemented by exactly one type, forever.

I wanted to know: does that actually help, or is it just ceremony we’ve all agreed to perform? So I ran a small experiment — building the same service two ways. One version wrapped everything in interfaces from day one. The other added interfaces only when a real need showed up. Let’s walk through what happened, and why the answer surprised me a little.

The Setup: Same Service, Two Philosophies

Both versions of the experiment implement a small order-processing service: fetch an order, validate it, apply a discount, and save it. Simple enough to reason about…

Ade Mawan

Interfaces Everywhere vs Interfaces Where Needed: A Go Architecture Experiment

A hands-on Go experiment comparing interfaces-everywhere against interfaces-where-needed — the results might change how you code.

The Setup: Same Service, Two Philosophies

Written by Ade Mawan

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