haphpiness

Closures and Variable Binding with use()

PHP closures explicitly capture variables from the enclosing scope with use(). This isn't a limitation — it's a feature. You always know exactly what a closure depends on, making the code easier to reason about and debug.

// Explicit capture — no hidden dependencies
$multiplier = 1.21;  // VAT rate
$applyVat = function (float $price) use ($multiplier): float {
    return $price * $multiplier;
};

// Capture by reference for stateful closures
function createCounter(int $start = 0): Closure {
    $count = $start;
    return function () use (&$count): int {
        return $count++;
    };
}
$counter = createCounter();
echo $counter(); // 0
echo $counter(); // 1

// Closures can bind to objects — powerful for DSLs
$closure = Closure::bind(function () {
    return $this->secret; // Access private property
}, $object, get_class($object));

// Middleware pattern with closures
$middleware = function (Request $request, Closure $next): Response {
    // Before
    $response = $next($request);
    // After
    return $response;
};

The explicit use() clause means you can look at any closure and immediately see its external dependencies. Combined with Closure::bind() and Closure::fromCallable(), PHP closures are flexible enough for any functional or object-oriented pattern.