0002: Error Handling Builds on Interfaces

Date: 2026-06-14 Status: Accepted

Context #

The learner has completed Lesson 0001 (Go interfaces: implicit satisfaction). The next step is error handling, which is a direct application of interfaces: Go's error type is just a single-method interface.

Insight #

Teaching error handling immediately after interfaces creates a powerful "aha" moment: everything from 0001 applies directly. errors.Is walks the error chain using interface satisfaction checks. Custom error types implement the error interface just like any other interface. Wrapping with %w creates an interface-compatible chain. This sequencing makes error handling feel natural rather than arbitrary.

The learner will immediately recognize error as the same pattern they just learned ("oh, it's just another interface"), which dramatically reduces cognitive load.

Consequences #

• Lesson 0002 will teach error handling through the interface lens
• Should emphasize errors.Is/errors.As: these are the most common in cloud-native code reviews
• Should include Kubernetes-style error patterns (structured errors, StatusError)
• Reference doc: error-handling-cheat-sheet.html
• The nil interface trap from 0001 reappears here (checking err != nil vs nil interface)