Standard PHP Library (SPL)

🎯 Key Points

• ✓ArrayIterator - Iterator wrapper omkring arrays med tilføjet funktionalitet
• ✓FilterIterator - Filter items during iteration baseret på custom logic
• ✓DirectoryIterator - Iterate over filesystem directories og files
• ✓RecursiveIteratorIterator - Iterate recursively gennem nested structures
• ✓SplStack - Last-In-First-Out (LIFO) data structure implementation
• ✓SplQueue - First-In-First-Out (FIFO) data structure implementation
• ✓SplHeap - Heap data structure for priority queues
• ✓SplObjectStorage - Map objects to data eller create object sets
• ✓SPL Exceptions - Specialized exception types (InvalidArgumentException, LogicException, etc)
• ✓Iterator interfaces - SeekableIterator, RecursiveIterator, OuterIterator
• ✓Countable & ArrayAccess - Interfaces for array-like behavior på objects
• ✓spl_autoload_register - Register autoloader functions for class loading

💻 Kode Eksempel

<?php

// SplStack - LIFO data structure
$stack = new SplStack();
$stack->push('Bottom');
$stack->push('Middle');
$stack->push('Top');

echo "Stack (LIFO):\n";
while (!$stack->isEmpty()) {
    echo $stack->pop() . "\n"; // Top, Middle, Bottom
}

// SplQueue - FIFO data structure
$queue = new SplQueue();
$queue->enqueue('First in line');
$queue->enqueue('Second in line');
$queue->enqueue('Third in line');

echo "\nQueue (FIFO):\n";
while (!$queue->isEmpty()) {
    echo $queue->dequeue() . "\n"; // First, Second, Third
}

// Custom FilterIterator
class EvenNumberFilter extends FilterIterator {
    public function accept(): bool {
        return $this->current() % 2 === 0;
    }
}

$numbers = new ArrayIterator([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
$evenNumbers = new EvenNumberFilter($numbers);

echo "\nEven numbers only:\n";
foreach ($evenNumbers as $num) {
    echo $num . " ";
}
echo "\n";

// SplObjectStorage - Object-to-data mapping
$storage = new SplObjectStorage();

class Product {
    public function __construct(public string $name) {}
}

$laptop = new Product('Laptop');
$mouse = new Product('Mouse');

$storage[$laptop] = ['price' => 1000, 'stock' => 5];
$storage[$mouse] = ['price' => 25, 'stock' => 50];

echo "\nProduct inventory:\n";
foreach ($storage as $product) {
    $data = $storage[$product];
    echo "{$product->name}: \${$data['price']} ({$data['stock']} in stock)\n";
}

// SPL Exceptions
function divideNumbers(float $a, float $b): float {
    if ($b === 0.0) {
        throw new InvalidArgumentException('Division by zero is not allowed');
    }
    return $a / $b;
}

try {
    echo "\n10 / 2 = " . divideNumbers(10, 2) . "\n";
    echo "10 / 0 = " . divideNumbers(10, 0) . "\n";
} catch (InvalidArgumentException $e) {
    echo "Error: {$e->getMessage()}\n";
}

// ArrayIterator with advanced features
$data = ['apple', 'banana', 'cherry', 'date'];
$iterator = new ArrayIterator($data);

echo "\nArrayIterator with seek:\n";
$iterator->seek(2); // Jump to index 2
echo "Current: {$iterator->current()}\n";
echo "Count: {$iterator->count()}\n";

⭐ Best Practices

• ✓Prefer SPL data structures over arrays når du har specifike use cases (stack, queue, heap)
• ✓Extend FilterIterator for reusable filtering logic i stedet for array_filter
• ✓Brug SPL exceptions for mere præcis error handling - InvalidArgumentException vs generic Exception
• ✓Kombiner SPL iterators med generator functions for memory-efficient data processing
• ✓Implement Countable og ArrayAccess interfaces for at give objects array-like behavior
• ✓Brug SplObjectStorage når du skal mappe objects til data uden at modificere object selv
• ✓Type hint SPL interfaces (Iterator, Countable) for bedre flexibility og testability
• ✓Cache SPL iterator instances når samme iteration sker multiple gange for performance