Refused Bequest

Also Known As

TL;DR

Explanation

Refused Bequest is a code smell where a subclass inherits behaviour from a parent but overrides it to do nothing, throws an exception, or simply ignores it. This is a strong signal that the inheritance hierarchy doesn't reflect a genuine is-a relationship. The fix depends on severity: if the subclass reuses some parent behaviour, extract a sibling class from the parent; if it shares no meaningful behaviour with the parent, replace inheritance with composition. The Liskov Substitution Principle is violated whenever a subclass refuses part of its parent's contract.

Common Misconception

Why It Matters

Common Mistakes

• Subclasses that throw UnsupportedOperationException for inherited methods — the interface contract is broken.
• Empty method overrides that silence inherited behaviour — the inheritance is wrong, not the method.
• Using inheritance for code reuse when composition would not impose the unwanted interface.
• Not using interfaces to define capability subsets — implement only what applies rather than inheriting everything.

Code Examples

// Child refuses to use methods inherited from parent
class ReadOnlyList extends ArrayList {
    public function add(\$item): void {
        throw new \RuntimeException('Read-only list cannot be modified');
    }
    public function remove(\$item): void {
        throw new \RuntimeException('Read-only list cannot be modified');
    }
}

// Fix: don't inherit what you can't use — use composition or a separate interface
interface ReadableList {
    public function get(int \$index): mixed;
    public function count(): int;
}

class ReadOnlyList implements ReadableList {
    public function __construct(private array \$items) {}
    public function get(int \$index): mixed { return \$this->items[\$index]; }
    public function count(): int { return count(\$this->items); }
    // No add/remove — they simply don't exist here
}

References

• ↗ https://refactoring.guru/smells/refused-bequest

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