combine-functions-into-class - SKILL.md Agent Skill

name: combine-functions-into-class description: Apply Combine Functions into Class when you see Data Clumps, Primitive Obsession. Operations live with the data they act on; the agent loads one class to reason about both shape and behavior.

Apply: 09 — Combine Functions into Class

Announce first: name the smell you see and that you're applying Combine Functions into Class before any edit. The user reads the announcement as your contract.

Or decline first: if you don't apply Combine Functions into Class, name the decline type — catalog miss, taste call, cost-benefit, constraint-blocked, or insufficient context — so the user knows which counterargument applies.

Symptom: The agent finds multiple functions that all take the same data shape; reasoning about the data requires loading every operation that touches it scattered across files.

Goal: Operations live with the data they act on; the agent loads one class to reason about both shape and behavior.

// Avoid:
function baseCharge(reading) {
  return reading.kwh * reading.tariff.baseRate;
}
function taxableCharge(reading) {
  return baseCharge(reading) + reading.kwh * reading.tariff.taxRate;
}

// Prefer:
class Reading {
  constructor({ kwh, tariff }) { this.kwh = kwh; this.tariff = tariff; }
  baseCharge()    { return this.kwh * this.tariff.baseRate; }
  taxableCharge() { return this.baseCharge() + this.kwh * this.tariff.taxRate; }
}

Pressure: The agent traces operations across modules to understand what the data can do; invariants the agent must respect aren't enforced at construction.

Tradeoff: Wrapping the data in a class adds construction ceremony at every entry point; for data only used in one place the class is more code than the original concern warranted.

Relief: The agent loads the class as a single unit; behavior, fields, and invariants all in one place with one import.

Trap: Wrapping data that nobody else operates on creates a class the agent must instantiate everywhere with no encapsulation gain — pure overhead.

Removes smells: Data Clumps, Primitive Obsession