<?php
declare(strict_types=1);

function add(int $a, int $b): int
{
    return $a + $b;
}

add(1, 2);     // OK
add(1, "2");   // TypeError! (without strict_types, "2" would be coerced to 2)
add(1, 2.0);   // TypeError! (float is not int in strict mode)

<?php
function process(int|string $id): void { /* ... */ }

function find(int $id): User|null  // equivalent to ?User
{
    return $this->repo->find($id);
}

// Common union: accepting array or single value
function normalize(string|array $input): array
{
    return is_array($input) ? $input : [$input];
}

<?php
// Must implement BOTH Countable AND Iterator
function processCollection(Countable&Iterator $items): void
{
    echo "Processing {$items->count()} items...";
    foreach ($items as $item) {
        handle($item);
    }
}

<?php
// Must be (A & B) OR null
function getCollection(): (Countable&Iterator)|null
{
    // ...
}

<?php
function process(string|int|null $value): string
{
    if ($value === null) {
        return 'nothing';  // narrowed: $value is null here
    }
    
    if (is_int($value)) {
        return (string) ($value * 2);  // narrowed: $value is int here
    }
    
    return strtoupper($value);  // narrowed: $value is string here
}

<?php
if ($shape instanceof Circle) {
    // PHP knows $shape is Circle — can access Circle-specific methods
    echo $shape->getRadius();
}

<?php
/**
 * @template T
 * @param class-string<T> $class
 * @return T
 */
function create(string $class): object
{
    return new $class();
}

/**
 * @template T
 * @param T[] $items
 * @return T|null
 */
function first(array $items): mixed
{
    return $items[0] ?? null;
}

# Install
composer require --dev phpstan/phpstan

# Run
vendor/bin/phpstan analyse src/ --level=9

composer require --dev vimeo/psalm
vendor/bin/psalm --init
vendor/bin/psalm