Reflection API

Also Known As

TL;DR

Explanation

The PHP Reflection API (ReflectionClass, ReflectionMethod, ReflectionProperty, ReflectionFunction, ReflectionParameter) enables runtime inspection of code structure — reading type declarations, attributes, docblocks, visibility, and default values without invoking the code. It underpins dependency injection containers (resolving constructor parameters), ORM hydration, serialisation libraries, and testing frameworks. Reflection is powerful but has a performance cost — production DI containers cache reflection results. PHP 8.0 Attributes provide a structured, performant alternative to docblock-parsed metadata.

Common Misconception

Why It Matters

Common Mistakes

• Using Reflection in hot code paths without caching results — ReflectionClass instantiation is expensive.
• Not caching reflected class metadata in a DI container — reflecting the same class on every request adds measurable overhead.
• Using Reflection to access private members of other classes in production code — breaks encapsulation.
• Not using PHP 8 Attributes instead of docblock parsing when possible — native attributes are faster and type-safe.

Code Examples

// Uncached reflection in a hot path:
function resolve(string $class): object {
    $ref = new ReflectionClass($class); // Expensive — not cached
    $params = $ref->getConstructor()->getParameters();
    // ... inject dependencies
}

// Inspect class structure at runtime
$ref = new ReflectionClass(OrderService::class);
echo $ref->getName();       // 'App\Domain\OrderService'
echo $ref->getShortName();  // 'OrderService'

$methods    = $ref->getMethods(ReflectionMethod::IS_PUBLIC);
$constructor = $ref->getConstructor();

// Read PHP 8.0+ attributes:
foreach ($ref->getMethods() as $method) {
    foreach ($method->getAttributes(Route::class) as $attr) {
        $route = $attr->newInstance();
        echo $route->path;
    }
}

// Instantiate without constructor (DI containers, test fixtures):
$instance = $ref->newInstanceWithoutConstructor();

Tags

Related Terms

References

• https://www.php.net/manual/en/book.reflection.php