array-sugar.md

T[] array sugar

xphp accepts the documentation-friendly T[] notation as shorthand for "array of T". It lowers to plain array at compile time. This is an xphp-specific convenience — the PHP RFC for generics explicitly bans the array<K, V> syntax, so xphp doesn't accept that.

Example

<?php
declare(strict_types=1);

namespace App;

class Collection<T> {
    private T[] $items = [];

    public function set(T[] $items): void {
        $this->items = $items;
    }

    public function all(): T[] {
        return $this->items;
    }

    // Two-dimensional sugar also works
    public function grid(): T[][] {
        return [$this->items, $this->items];
    }
}

What gets emitted

T[] lowers to plain array in every position. The element-type enforcement still happens wherever T appears in a position PHP can enforce — usually a variadic param (T ...$items) or single-element setter (T $x):

namespace XPHP\Generated\App\Collection;

class T_<hash-of-int> implements \App\Collection {
    private array $items = [];
    public function set(array $items): void { $this->items = $items; }
    public function all(): array { return $this->items; }
    public function grid(): array { return [$this->items, $this->items]; }
}

Rules

• T[], Name[], and chained T[][], T[][][], ... all lower to plain array.
• Mixing concrete and generic: User[] lowers to array (with the same enforcement caveat).
• array<K, V> (RFC-banned form) is not accepted.
• The sugar is a parser convenience; it doesn't affect monomorphization (no extra specializations from it).

Caveats

• Element-type enforcement only happens where T appears outside the [] sugar. If your generic API exposes T[] everywhere and never takes a single T, runtime type checks won't catch a mistyped element. Add a variadic __construct(T ...$items) or a set(T $x) setter to anchor enforcement.

See also

• Test fixture: test/fixture/compile/array_sugar/
• Related: classes and interfaces