Move Field

Removes smells

Symptom

The agent finds a field on class A whose value is determined by data on class B; reasoning about the field's value requires loading B to verify the derivation.

Goal

Each field lives in the class that determines its value; reading the field and reading the data that determines it happen in the same class file.

Before the refactoring

class Customer {
  plan;
  discountRate;
}
// every customer in a given plan gets the same rate:
customers.forEach(c => c.discountRate = c.plan.kind === 'gold' ? 0.15 : 0.05);

After the refactoring

class Plan {
  kind;
  discountRate;
}
class Customer { plan; }
customer.plan.discountRate;

Example source: Illustrative example written for this site, not a quotation from any source.

Pressure

Every consumer must maintain the cross-class invariant; the agent verifying any change must coordinate updates across both classes.

Tradeoff

Every previous reader of the field now loads the new owner class to read it; tokens that previously stayed in one file now span two, and the agent follows the new boundary at every read site.

Relief

Mutations to the field stay inside the class that determines its value; the agent reads one class file to predict both the field's value and the data that drives it.

Trap

Moving fields purely on derivation grounds — without checking whether the original class's identity depends on the field's presence — breaks consumer expectations the agent didn't model.