PHP RFC: Bound-Erased Generic Types

• Version: 0.1
• Date: 2026-05-06
• Author: Seifeddine Gmati, azjezz@carthage.software
• Status: Draft

This RFC proposes adding generic type syntax to PHP. Type parameters declared on classes, interfaces, traits, functions, methods, closures, and arrow functions are erased to their declared bounds at compile time: the runtime enforces the bound, while parametricity is verified by static analysis tools. Type information that today lives in @template and @param Container<int> docblocks becomes first-class language syntax, exposed through a new Reflection API.

<?php
 
final readonly class Box<+T: mixed> {
    public function __construct(
      public T $value,
    ) {}
 
    public function zip<O>(O $value): self<Pair<T, O>> {
        return new self(new Pair($this->value, $value));
    }
}
 
function first<T>(array<T> $items): ?T {
    return $items[0] ?? null;
}
 
$box = new Box::<string>("hello, world");

TBD.

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Next PHP 8.x.

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None at this time.

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TBD.

None at this time.

• 2026-05-06: Initial draft.