incremental-implementation

Incremental Implementation

Overview

The most dangerous coding session is the one where you write 500 lines, hit "save," and pray. By the time you test, you've introduced so many variables that debugging becomes whack-a-mole. Incremental implementation is the discipline of keeping the system working at every step — not just at the end.

The incremental contract: Every commit must leave the system in a working, testable state. Implement one vertical slice (end-to-end functionality for a subset of the feature), verify it, commit it, then expand. If you can't demo the current state to a user, the increment is too large.

Real-world impact: Engineers who work in small increments catch bugs immediately (when they're trivial to fix) rather than at the end (when they're entangled with 20 other changes). This is the practice that separates engineers who ship reliably from engineers who miss deadlines.

When to Use

• Implementing any multi-file change
• Building a new feature from a task breakdown
• Refactoring existing code
• Any time you're tempted to write more than ~100 lines before testing

When NOT to use: Single-file, single-function changes where the scope is already minimal.

The Increment Cycle

┌──────────────────────────────────────┐
│                                      │
│   Implement ──→ Test ──→ Verify ──┐  │
│       ▲                           │  │
│       └───── Commit ◄─────────────┘  │
│              │                       │
│              ▼                       │
│          Next slice                  │
│                                      │
└──────────────────────────────────────┘

For each slice:

1. Implement the smallest complete piece of functionality
2. Test — run the test suite (or write a test if none exists)
3. Verify — confirm the slice works as expected (tests pass, build succeeds, manual check)
4. Commit -- save your progress with a descriptive message (see git-workflow-and-versioning for atomic commit guidance)
5. Move to the next slice — carry forward, don't restart