Replace Subclass with Delegate

Symptom

A subclass that overrides several methods to implement variant behavior; the agent reasoning about polymorphic dispatch must enumerate variants across the hierarchy.

Goal

Variants live in delegate objects the host holds and forwards to; the agent reads one host class plus the held delegate's interface instead of climbing an inheritance chain to predict behavior.

Before the refactoring

class Booking { /* ... */ }
class PremiumBooking extends Booking {
/* overrides several methods */
}

After the refactoring

class Booking {
type; // 'standard' | premium delegate
charge() { return this.type.charge(this); }
}
Example source: Illustrative example written for this site, not a quotation from any source.
Pressure

Behavior can't change at runtime; combining variants requires multiple inheritance the agent must work around; Liskov violations hide in override behavior.

Tradeoff

Composition is more verbose at construction sites; the agent loses syntactic polymorphism and must verify behavior through explicit delegation calls.

Relief

Behavior changes at runtime by swapping the delegate; the agent reasons against one host signature plus the delegate's interface, without loading the inheritance graph to verify which override applies to a given instance.

Trap

Replacing inheritance with delegation on hierarchies where every subclass honors the parent's contract adds construction-site setup and a forwarding method per parent method without changing what the agent's generated calls do.