What to Open, What to Close: A Pragmatic Guide to Interface Design

The playbook for building software seams that bend with change, not break.

Maneesh Chaturvedi

— 1 min read

The playbook for building software seams that bend with change, not break.

Quick take: Every architectural regret starts as a small “harmless” interface. Four posts, twenty patterns, and dozens of code snippets show you how to choose the seam that stays harmless — no matter how your product mutates.

Why this series exists

Interfaces are the pressure valves of a codebase. Pick the wrong valve:

  • new features ricochet through unrelated files,
  • plug‑ins fight your core types,
  • or consumers rage when their integration breaks.

Pick the right one and change flows like water.

This series is a hands‑on field guide to that choice — rooted in Java, Go, TypeScript, Scala, and Kotlin, but focused on principles you can port anywhere.

The 4-Part Series

Part 1: The Expression Problem & Interface Shape

“Should extensibility favour behaviours or data variants?” → trade‑offs, guiding heuristics, code walkthroughs.

Read Part 1 →

Part 2: Designing for Real-World Volatility

How to quarantine fast‑changing behaviours (audits, reports, analytics) without polluting domain logic.

Read Part 2 →

Part 3: Preventing Fragile Base Class Bugs

Inheritance landmines, composition refactors, sealed abstractions, and hook patterns that keep OO trees from toppling.

Coming Soon

Part 4: Evolving Interfaces Without Breaking Consumers

Versioning, schema evolution, plugin contracts, and runtime type‑safety techniques that keep dependents unbroken.

Coming Soon

Who will benefit

  • Backend & API engineers crafting contracts that must survive quarterly rewrites
  • Architects & tech leads responsible for plug‑in ecosystems, microservices, or modular monoliths
  • Senior devs tired of “one‑line” changes spawning 15‑file PRs

If you’ve ever whispered “I hope this change doesn’t ripple…”, this series is for you.

Stay in the loop

  • Follow @maneesh‑chaturvedi here on Medium for future deep dives.
  • Have a colleague firefighting interface debt? Share this series — help them refactor less and ship more. 🚀

Ready? Start with Part 1 and learn why half of extensibility is knowing what not to extend.

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