DNF Types (PHP 8.2)

TL;DR

Explanation

DNF type: (A&B)|C where intersections appear in parentheses within a union. PHP 8.1 added intersection types (A&B — object must implement both). PHP 8.2 adds DNF — combining intersections with unions: (Countable&Traversable)|null means either null OR an object implementing both Countable and Traversable. Rules: intersections must be in parentheses within unions. Cannot have redundant types. Cannot duplicate types within a union. Use cases: nullable intersection types (the most common: (A&B)|null), optional complex type parameters, return types that are either an intersection or a primitive.

Common Misconception

Why It Matters

Common Mistakes

• Forgetting parentheses around intersection in union — syntax error.
• Redundant types in union — (A&A)|B is invalid.
• Using DNF where simple union suffices — only needed for intersections in unions.

Code Examples

// PHP 8.1 — no way to express nullable intersection:
function process(Countable&Iterator $items): void {} // Non-nullable only

// PHP 8.2 DNF — nullable intersection:
function process((Countable&Iterator)|null $items): void {
    if ($items === null) return;
    // $items is guaranteed to be both Countable AND Iterator
}

// Other uses:
function transform((Stringable&JsonSerializable)|array $data): string {}

References

• ↗ https://www.php.net/manual/en/migration82.new-features.php

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