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    <h3>Editing: CallableType.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php declare(strict_types=1);
/*
 * This file is part of sebastian/type.
 *
 * (c) Sebastian Bergmann &lt;sebastian@phpunit.de&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace SebastianBergmann\Type;

use function assert;
use function class_exists;
use function count;
use function explode;
use function function_exists;
use function is_array;
use function is_object;
use function is_string;
use Closure;
use ReflectionClass;
use ReflectionException;
use ReflectionObject;

final class CallableType extends Type
{
    /**
     * @var bool
     */
    private $allowsNull;

    public function __construct(bool $nullable)
    {
        $this-&gt;allowsNull = $nullable;
    }

    /**
     * @throws RuntimeException
     */
    public function isAssignable(Type $other): bool
    {
        if ($this-&gt;allowsNull &amp;&amp; $other instanceof NullType) {
            return true;
        }

        if ($other instanceof self) {
            return true;
        }

        if ($other instanceof ObjectType) {
            if ($this-&gt;isClosure($other)) {
                return true;
            }

            if ($this-&gt;hasInvokeMethod($other)) {
                return true;
            }
        }

        if ($other instanceof SimpleType) {
            if ($this-&gt;isFunction($other)) {
                return true;
            }

            if ($this-&gt;isClassCallback($other)) {
                return true;
            }

            if ($this-&gt;isObjectCallback($other)) {
                return true;
            }
        }

        return false;
    }

    public function name(): string
    {
        return 'callable';
    }

    public function allowsNull(): bool
    {
        return $this-&gt;allowsNull;
    }

    /**
     * @psalm-assert-if-true CallableType $this
     */
    public function isCallable(): bool
    {
        return true;
    }

    private function isClosure(ObjectType $type): bool
    {
        return !$type-&gt;className()-&gt;isNamespaced() &amp;&amp; $type-&gt;className()-&gt;simpleName() === Closure::class;
    }

    /**
     * @throws RuntimeException
     */
    private function hasInvokeMethod(ObjectType $type): bool
    {
        $className = $type-&gt;className()-&gt;qualifiedName();
        assert(class_exists($className));

        try {
            $class = new ReflectionClass($className);
            // @codeCoverageIgnoreStart
        } catch (ReflectionException $e) {
            throw new RuntimeException(
                $e-&gt;getMessage(),
                (int) $e-&gt;getCode(),
                $e
            );
            // @codeCoverageIgnoreEnd
        }

        if ($class-&gt;hasMethod('__invoke')) {
            return true;
        }

        return false;
    }

    private function isFunction(SimpleType $type): bool
    {
        if (!is_string($type-&gt;value())) {
            return false;
        }

        return function_exists($type-&gt;value());
    }

    private function isObjectCallback(SimpleType $type): bool
    {
        if (!is_array($type-&gt;value())) {
            return false;
        }

        if (count($type-&gt;value()) !== 2) {
            return false;
        }

        if (!isset($type-&gt;value()[0], $type-&gt;value()[1])) {
            return false;
        }

        if (!is_object($type-&gt;value()[0]) || !is_string($type-&gt;value()[1])) {
            return false;
        }

        [$object, $methodName] = $type-&gt;value();

        return (new ReflectionObject($object))-&gt;hasMethod($methodName);
    }

    private function isClassCallback(SimpleType $type): bool
    {
        if (!is_string($type-&gt;value()) &amp;&amp; !is_array($type-&gt;value())) {
            return false;
        }

        if (is_string($type-&gt;value())) {
            if (strpos($type-&gt;value(), '::') === false) {
                return false;
            }

            [$className, $methodName] = explode('::', $type-&gt;value());
        }

        if (is_array($type-&gt;value())) {
            if (count($type-&gt;value()) !== 2) {
                return false;
            }

            if (!isset($type-&gt;value()[0], $type-&gt;value()[1])) {
                return false;
            }

            if (!is_string($type-&gt;value()[0]) || !is_string($type-&gt;value()[1])) {
                return false;
            }

            [$className, $methodName] = $type-&gt;value();
        }

        assert(isset($className) &amp;&amp; is_string($className) &amp;&amp; class_exists($className));
        assert(isset($methodName) &amp;&amp; is_string($methodName));

        try {
            $class = new ReflectionClass($className);

            if ($class-&gt;hasMethod($methodName)) {
                $method = $class-&gt;getMethod($methodName);

                return $method-&gt;isPublic() &amp;&amp; $method-&gt;isStatic();
            }
            // @codeCoverageIgnoreStart
        } catch (ReflectionException $e) {
            throw new RuntimeException(
                $e-&gt;getMessage(),
                (int) $e-&gt;getCode(),
                $e
            );
            // @codeCoverageIgnoreEnd
        }

        return false;
    }
}
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