Switch Statement Smell

Also Known As

TL;DR

Explanation

Switch statements on a type or status field scattered across a codebase indicate that object-oriented polymorphism is the appropriate design. Each time a new type is added, every switch must be updated — a violation of the Open/Closed Principle. The refactoring is Replace Conditional with Polymorphism: create a class hierarchy where each subclass provides its own implementation of the varying behaviour. PHP 8.0's match expression is not a remedy for this smell — it's a better syntax for the same structural problem.

Common Misconception

Why It Matters

Common Mistakes

• Type-switching on a string, integer, or enum that represents a known set of types — use polymorphism instead.
• The same switch appearing in multiple places across the codebase — shotgun surgery.
• Not using match expressions in PHP 8 which at least provide exhaustiveness checking.
• Switch on type in service code when the decision should be in the domain object itself.

Code Examples

// Switch on type — must update for every new animal
function makeSound(string \$type): string {
    switch (\$type) {
        case 'dog': return 'Woof';
        case 'cat': return 'Meow';
        default:    return '???';
    }
}

// Polymorphism — each class knows its own behaviour
interface Animal { public function makeSound(): string; }
class Dog implements Animal { public function makeSound(): string { return 'Woof'; } }
class Cat implements Animal { public function makeSound(): string { return 'Meow'; } }

function play(Animal \$a): void { echo \$a->makeSound(); }
// Caller never changes when a new animal is added

References

• ↗ https://refactoring.guru/smells/switch-statements

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