Laravel学习笔记之PHP反射(Reflection) (上)

说明：Laravel中经常使用PHP的反射特性来设计代码，本文主要学习PHP的反射特性，来提高写代码时的设计质量。PHP提供一套检测class, interface, trait, property, method的两个工具包：Introspection Functions和Reflection API，类似于探针一样的东西来探测这些一等公民。本文先看下Introspection Functions的使用。

开发环境: Laravel5.3 + PHP7

Introspection Functions

Introspection Functions是用来操作object class的一些函数，PHP提供了大量的Introspection Functions来操作class, interface, trait, method, property:

1. class_exists()

2. interface_exists()

3. method_exists()

4. property_exists()

5. trait_exists()

6. class_alias()

7. get_class()

8. get_parent_class()

9. get_called_class()

10. get_class_methods()

11. get_class_vars()

12. get_object_vars()

13. is_subclass_of()

14. is_a()

class_exists()

Laravel源码中好多个地方使用到class_exists()方法来判断指定类是否存在，如\Illuminate\Database\Connection::isDoctrineAvailable()的源码：

    public function isDoctrineAvailable()
    {
        return class_exists('Doctrine\DBAL\Connection'); // Doctrine\DBAL\Connection::class类是否存在，大小写不敏感
    }

写个PHPUnit测试下(爆绿灯，说明是正确的，这里不截图了。后面所有Introspection的测试都放在IntrospectionTest这个单元测试里)：

namespace MyRightCapital\Container\Tests;

class IntrospectionTest extends \PHPUnit_Framework_TestCase
{
    public function testClassExists()
    {
        // Arrange
        
        // Actual
        $class_exists = class_exists(TestClassExists::class);
        // Assert
        $this->assertTrue($class_exists);
    }
}

class TestClassExists
{
    
}

interface_exists()

interface_exists()是用来检查接口是否存在，写个PHPUnit测试下，爆绿灯：

namespace MyRightCapital\Container\Tests;

class IntrospectionTest extends \PHPUnit_Framework_TestCase
{
    public function testInterfaceExists()
    {
        // Arrange
        
        // Actual
        $interface_exists = interface_exists(TestInterfaceExists::class);
        // Assert
        $this->assertTrue($interface_exists);
    }
}

interface TestInterfaceExists
{
    
}

method_exists()

检查类的方法(private,protected,public)是否存在于指定的类对象或类名中，Laravel中很多处用到了这个函数，如Application中的register()检查service provider中register是否存在，和bootProvider()中检查service provider中boot()方法是否存在：

public function register($provider, $options = [], $force = false)
{
    ...
    
    if (method_exists($provider, 'register')) {
            $provider->register();
    }
    
    ...
}
protected function bootProvider(ServiceProvider $provider)
{
    if (method_exists($provider, 'boot')) {
        return $this->call([$provider, 'boot']);
    }
}

这里写个PHPUnit测试下，爆绿灯：

    public function testMethodExists()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $object_method_exists1    = method_exists($test_class_exists, 'testPrivateMethodExists');
        $object_method_exists2    = method_exists($test_class_exists, 'testProtectedMethodExists');
        $object_method_exists3    = method_exists($test_class_exists, 'testPublicMethodExists');
        $classname_method_exists1 = method_exists(TestClassExists::class, 'testPrivateMethodExists');
        $classname_method_exists2 = method_exists(TestClassExists::class, 'testProtectedMethodExists');
        $classname_method_exists3 = method_exists(TestClassExists::class, 'testPublicMethodExists');
        
        // Assert
        $this->assertTrue($object_method_exists1);
        $this->assertTrue($object_method_exists2);
        $this->assertTrue($object_method_exists3);
        $this->assertTrue($classname_method_exists1);
        $this->assertTrue($classname_method_exists2);
        $this->assertTrue($classname_method_exists3);
    }
    
    
    class TestClassExists
    {
        private function testPrivateMethodExists()
        {
        }
        
        protected function testProtectedMethodExists()
        {
        }
        
        public function testPublicMethodExists()
        {
        }
    }

property_exists()

检查该属性(private, protected, public)是否存在于类对象或类名中，Laravel很多地方用到了该函数，如\Illuminate\Foundation\Auth\RedirectsUsers::redirectPath()源码：

    public function redirectPath()
    {
        return property_exists($this, 'redirectTo') ? $this->redirectTo : '/home';
    }

写个PHPUnit测试下该函数，爆绿灯：

    // class IntrospectionTest
    public function testPropertyExists()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $private_property1   = property_exists($test_class_exists, 'testPrivatePropertyExists');
        $private_property2   = property_exists(TestClassExists::class, 'testPrivatePropertyExists');
        $protected_property1 = property_exists($test_class_exists, 'testProtectedPropertyExists');
        $protected_property2 = property_exists(TestClassExists::class, 'testProtectedPropertyExists');
        $public_property1    = property_exists($test_class_exists, 'testPublicPropertyExists');
        $public_property2    = property_exists(TestClassExists::class, 'testPublicPropertyExists');
        
        // Assert
        $this->assertTrue($private_property1);
        $this->assertTrue($private_property2);
        $this->assertTrue($protected_property1);
        $this->assertTrue($protected_property2);
        $this->assertTrue($public_property1);
        $this->assertTrue($public_property2);
    }
    
    
    class TestClassExists
    {
        private   $testPrivatePropertyExists;
        protected $testProtectedPropertyExists;
        public    $testPublicPropertyExists;
    }

trait_exists()

检查trait是否存在，写下PHPUnit测试，爆绿灯：

    // class IntrospectionTest
    public function testTraitExists()
    {
        // Arrange
        
        // Actual
        $test_trait_exists = trait_exists(TestTraitExists::class);
        
        // Assert
        $this->assertTrue($test_trait_exists);
    }
    
    trait TestTraitExists
    {
    
    }

class_alias()

给指定类取别名，Laravel中只有一处使用了class_alias()，用来给config/app.php中$aliases[ ]注册别名，可看下Laravel学习笔记之bootstrap源码解析，看下Laravel中如何使用的：

    public function load($alias)
    {
        if (isset($this->aliases[$alias])) {
            return class_alias($this->aliases[$alias], $alias);
        }
    }

写个PHPUnit测试，爆绿灯：

    public function testClassAlias()
    {
        // Arrange
        class_alias(TestClassExists::class, 'MyRightCapital\Container\Tests\AliasTestClassExists');
        $test_class_exists = new TestClassExists();
        
        // Actual
        $actual = new AliasTestClassExists();
        
        //Assert
        $this->assertInstanceOf(TestClassExists::class, $actual);
        $this->assertInstanceOf(AliasTestClassExists::class, $test_class_exists);
    }

get_class()

get_class()获取对象的类名，这个函数在Laravel中大量地方在用了，如Application::getProvider($provider)方法，是个很好用的方法：

    public function getProvider($provider)
    {
        $name = is_string($provider) ? $provider : get_class($provider);

        return Arr::first($this->serviceProviders, function ($value) use ($name) {
            return $value instanceof $name;
        });
    }

写个PHPUnit测试，爆绿灯：

    public function testGetClass()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $class_name = get_class($test_class_exists);
        
        // Assert
        $this->assertSame(TestClassExists::class, $class_name);
    }

get_parent_class()

get_parent_class()是用来获取类的父类名，目前Laravel中还没用到这个函数，传入的可以是子类对象或者子类名，写个PHPUnit测试下：

    // namespace MyRightCapital\Container\Tests;
    // class IntrospectionTest extends \PHPUnit_Framework_TestCase
    public function testGetParentClass()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $parent_class1 = get_parent_class($child_class);
        $parent_class2 = get_parent_class(ChildClass::class);
        
        // Assert
        $this->assertSame(ParentClass::class, $parent_class1);
        $this->assertSame(ParentClass::class, $parent_class2);
    }
    
    class ChildClass extends ParentClass 
    {
        
    }
    
    class ParentClass
    {
        
    }

get_called_class()

get_called_class()获取后期静态绑定类即实际调用类的名称，Laravel中还没使用到该函数，不妨写个测试看下如何使用：

    // namespace MyRightCapital\Container\Tests;
    // class IntrospectionTest extends \PHPUnit_Framework_TestCase
    public function testGetCalledClass()
    {
        // Arrange
        $child_class  = new ChildClass();
        $parent_class = new ParentClass();
        
        // Actual
        $child_called_class = $child_class->testGetCalledClass();
        $parent_called_class = $parent_class->testGetCalledClass();
        
        // Assert
        $this->assertSame(ChildClass::class, $child_called_class);
        $this->assertSame(ParentClass::class, $parent_called_class);
    }
    
    class ChildClass extends ParentClass
    {
        
    }
    
    class ParentClass
    {
        public function testGetCalledClass()
        {
            return get_called_class();
        }
    }

get_class_methods()

get_class_methods()用来获取类的方法名组成一个数组(测试只能是public)，Laravel只有一处用到了该方法\Illuminate\Database\Eloquent\Model::cacheMutatedAttributes() :line 3397,这里写个PHPUnit测试，爆绿灯：

    public function testGetClassMethod()
    {
        // Arrange
        $get_class_methods1 = get_class_methods(ChildClass::class);
        $get_class_methods2 = get_class_methods(new ChildClass());
        
        // Actual
        
        // Assert
        $this->assertFalse(in_array('testPrivateGetClassMethod', $get_class_methods1, true));
        $this->assertFalse(in_array('testPrivateGetClassMethod', $get_class_methods2, true));
        $this->assertFalse(in_array('testProtectedGetClassMethod', $get_class_methods1, true));
        $this->assertFalse(in_array('testProtectedGetClassMethod', $get_class_methods2, true));
        $this->assertTrue(in_array('testPublicGetClassMethod', $get_class_methods1, true));
        $this->assertTrue(in_array('testPublicGetClassMethod', $get_class_methods2, true));
        $this->assertTrue(in_array('testGetCalledClass', $get_class_methods1, true));
        $this->assertTrue(in_array('testGetCalledClass', $get_class_methods2, true));
    }
    
    class ChildClass extends ParentClass
    {
        private function testPrivateGetClassMethod()
        {
        }
        
        protected function testProtectedGetClassMethod()
        {
        }
        
        public function testPublicGetClassMethod()
        {
        }
    }

get_class_vars()

get_class_vars()只会读取类的public属性组成一个数组，类似于get_class_methods()，若属性没有默认值就为null，目前Laravel中还未使用，看下PHPUnit测试：

    public function testGetClassVars()
    {
        // Arrange
        
        // Actual
        $class_vars = get_class_vars(ChildClass::class);
        
        // Assert
        $this->assertArrayNotHasKey('privateNoDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('privateDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('protectedNoDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('protectedDefaultVar', $class_vars);
        $this->assertEmpty($class_vars['publicNoDefaultVar']);
        $this->assertEquals('public_laravel', $class_vars['publicDefaultVar']);
    }
    
    class ChildClass extends ParentClass
    {
        private   $privateNoDefaultVar;
        private   $privateDefaultVar   = 'private_laravel';
        protected $protectedNoDefaultVar;
        protected $protectedDefaultVar = 'protected_laravel';
        public    $publicNoDefaultVar;
        public    $publicDefaultVar    = 'public_laravel';
   }     

get_object_vars()

get_object_vars()只会读取对象的public属性组成一个数组，类似于get_class_vars(), get_class_methods()，且属性没有默认值就是null，Laravel中只有一处使用到\Illuminate\Mail\Jobs\HandleQueuedMessage::__sleep() :line 78，写个PHPUnit测试下，爆绿灯：

    public function testGetObjectVars()
    {
        // Arrange
        $get_object_vars = new TestGetObjectVars(1, 2, 3);
        
        // Actual
        $object_vars = get_object_vars($get_object_vars);
        
        // Assert
        $this->assertArrayNotHasKey('x', $object_vars);
        $this->assertArrayNotHasKey('y', $object_vars);
        $this->assertEquals(3, $object_vars['z']);
        $this->assertArrayNotHasKey('dot1', $object_vars);
        $this->assertArrayNotHasKey('dot2', $object_vars);
        $this->assertArrayNotHasKey('circle1', $object_vars);
        $this->assertArrayNotHasKey('circle2', $object_vars);
        $this->assertEquals(10, $object_vars['line1']);
        $this->assertEmpty($object_vars['line2']);
    }
    
    class TestGetObjectVars
    {
        private   $x;
        protected $y;
        public    $z;
        private   $dot1    = 10;
        private   $dot2;
        protected $circle1 = 20;
        protected $circle2;
        public    $line1   = 10;
        public    $line2;
        
        public function __construct($x, $y, $z)
        {
            
            $this->x = $x;
            $this->y = $y;
            $this->z = $z;
        }
    }

is_subclass_of()

is_subclass_of()用来判断给定类对象是否是另一给定类名的子类，Laravel中有用到，这里写下PHPUnit测试，爆绿灯：

    public function testIsSubclassOf()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $is_subclass = is_subclass_of($child_class, ParentClass::class);
        
        // Assert
        $this->assertTrue($is_subclass);
    }

is_a()

is_a()用来判定给定类对象是否是另一给定类名的对象或是子类，和is_subclass_of()有点类似，只是is_a()还可以判定是不是该类的对象，is_a()类似于instanceof操作符，Laravel中还没用到这个方法，这里写个PHPUnit测试，爆绿灯：

    public function testIsA()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $is_object   = is_a($child_class, ChildClass::class);
        $is_subclass = is_a($child_class, ParentClass::class);
        
        // Assert
        $this->assertTrue($is_object);
        $this->assertTrue($is_subclass);
    }

最后，给下整个PHPUnit的测试代码：

<?php

namespace MyRightCapital\Container\Tests;

class IntrospectionTest extends \PHPUnit_Framework_TestCase
{
    public function testClassExists()
    {
        // Arrange
        
        // Actual
        $class_exists = class_exists(TestClassExists::class);
        // Assert
        $this->assertTrue($class_exists);
    }
    
    public function testInterfaceExists()
    {
        // Arrange
        
        // Actual
        $interface_exists = interface_exists(TestInterfaceExists::class);
        // Assert
        $this->assertTrue($interface_exists);
    }
    
    public function testMethodExists()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $object_method_exists1    = method_exists($test_class_exists, 'testPrivateMethodExists');
        $object_method_exists2    = method_exists($test_class_exists, 'testProtectedMethodExists');
        $object_method_exists3    = method_exists($test_class_exists, 'testPublicMethodExists');
        $classname_method_exists1 = method_exists(TestClassExists::class, 'testPrivateMethodExists');
        $classname_method_exists2 = method_exists(TestClassExists::class, 'testProtectedMethodExists');
        $classname_method_exists3 = method_exists(TestClassExists::class, 'testPublicMethodExists');
        
        // Assert
        $this->assertTrue($object_method_exists1);
        $this->assertTrue($object_method_exists2);
        $this->assertTrue($object_method_exists3);
        $this->assertTrue($classname_method_exists1);
        $this->assertTrue($classname_method_exists2);
        $this->assertTrue($classname_method_exists3);
    }
    
    public function testPropertyExists()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $private_property1   = property_exists($test_class_exists, 'testPrivatePropertyExists');
        $private_property2   = property_exists(TestClassExists::class, 'testPrivatePropertyExists');
        $protected_property1 = property_exists($test_class_exists, 'testProtectedPropertyExists');
        $protected_property2 = property_exists(TestClassExists::class, 'testProtectedPropertyExists');
        $public_property1    = property_exists($test_class_exists, 'testPublicPropertyExists');
        $public_property2    = property_exists(TestClassExists::class, 'testPublicPropertyExists');
        
        // Assert
        $this->assertTrue($private_property1);
        $this->assertTrue($private_property2);
        $this->assertTrue($protected_property1);
        $this->assertTrue($protected_property2);
        $this->assertTrue($public_property1);
        $this->assertTrue($public_property2);
    }
    
    public function testTraitExists()
    {
        // Arrange
        
        // Actual
        $test_trait_exists = trait_exists(TestTraitExists::class);
        
        // Assert
        $this->assertTrue($test_trait_exists);
    }
    
    public function testClassAlias()
    {
        // Arrange
        class_alias(TestClassExists::class, 'MyRightCapital\Container\Tests\AliasTestClassExists');
        $test_class_exists = new TestClassExists();
        
        // Actual
        $actual = new AliasTestClassExists();
        
        //Assert
        $this->assertInstanceOf(TestClassExists::class, $actual);
        $this->assertInstanceOf(AliasTestClassExists::class, $test_class_exists);
    }
    
    public function testGetClass()
    {
        // Arrange
        $test_class_exists = new TestClassExists();
        
        // Actual
        $class_name = get_class($test_class_exists);
        
        // Assert
        $this->assertSame(TestClassExists::class, $class_name);
    }
    
    public function testGetParentClass()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $parent_class1 = get_parent_class($child_class);
        $parent_class2 = get_parent_class(ChildClass::class);
        
        // Assert
        $this->assertSame(ParentClass::class, $parent_class1);
        $this->assertSame(ParentClass::class, $parent_class2);
    }
    
    public function testGetCalledClass()
    {
        // Arrange
        $child_class  = new ChildClass();
        $parent_class = new ParentClass();
        
        // Actual
        $child_called_class  = $child_class->testGetCalledClass();
        $parent_called_class = $parent_class->testGetCalledClass();
        
        // Assert
        $this->assertSame(ChildClass::class, $child_called_class);
        $this->assertSame(ParentClass::class, $parent_called_class);
    }
    
    public function testInArray()
    {
        $this->assertTrue(in_array('a', ['a', 'b', 1], true));
    }
    
    public function testGetClassMethod()
    {
        // Arrange
        $get_class_methods1 = get_class_methods(ChildClass::class);
        $get_class_methods2 = get_class_methods(new ChildClass());
        
        // Actual
        
        // Assert
        $this->assertFalse(in_array('testPrivateGetClassMethod', $get_class_methods1, true));
        $this->assertFalse(in_array('testPrivateGetClassMethod', $get_class_methods2, true));
        $this->assertFalse(in_array('testProtectedGetClassMethod', $get_class_methods1, true));
        $this->assertFalse(in_array('testProtectedGetClassMethod', $get_class_methods2, true));
        $this->assertTrue(in_array('testPublicGetClassMethod', $get_class_methods1, true));
        $this->assertTrue(in_array('testPublicGetClassMethod', $get_class_methods2, true));
        $this->assertTrue(in_array('testGetCalledClass', $get_class_methods1, true));
        $this->assertTrue(in_array('testGetCalledClass', $get_class_methods2, true));
    }
    
    public function testGetClassVars()
    {
        // Arrange
        
        // Actual
        $class_vars = get_class_vars(ChildClass::class);
        
        // Assert
        $this->assertArrayNotHasKey('privateNoDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('privateDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('protectedNoDefaultVar', $class_vars);
        $this->assertArrayNotHasKey('protectedDefaultVar', $class_vars);
        $this->assertEmpty($class_vars['publicNoDefaultVar']);
        $this->assertEquals('public_laravel', $class_vars['publicDefaultVar']);
    }
    
    public function testGetObjectVars()
    {
        // Arrange
        $get_object_vars = new TestGetObjectVars(1, 2, 3);
        
        // Actual
        $object_vars = get_object_vars($get_object_vars);
        
        // Assert
        $this->assertArrayNotHasKey('x', $object_vars);
        $this->assertArrayNotHasKey('y', $object_vars);
        $this->assertEquals(3, $object_vars['z']);
        $this->assertArrayNotHasKey('dot1', $object_vars);
        $this->assertArrayNotHasKey('dot2', $object_vars);
        $this->assertArrayNotHasKey('circle1', $object_vars);
        $this->assertArrayNotHasKey('circle2', $object_vars);
        $this->assertEquals(10, $object_vars['line1']);
        $this->assertEmpty($object_vars['line2']);
    }
    
    public function testIsSubclassOf()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $is_subclass = is_subclass_of($child_class, ParentClass::class);
        
        // Assert
        $this->assertTrue($is_subclass);
    }
    
    public function testIsA()
    {
        // Arrange
        $child_class = new ChildClass();
        
        // Actual
        $is_object = is_a($child_class, ChildClass::class);
        $is_subclass = is_a($child_class, ParentClass::class);
        
        // Assert
        $this->assertTrue($is_object);
        $this->assertTrue($is_subclass);
    }
}

class TestGetObjectVars
{
    private   $x;
    protected $y;
    public    $z;
    private   $dot1    = 10;
    private   $dot2;
    protected $circle1 = 20;
    protected $circle2;
    public    $line1   = 10;
    public    $line2;
    
    public function __construct($x, $y, $z)
    {
        
        $this->x = $x;
        $this->y = $y;
        $this->z = $z;
    }
}

class ChildClass extends ParentClass
{
    private   $privateNoDefaultVar;
    private   $privateDefaultVar   = 'private_laravel';
    protected $protectedNoDefaultVar;
    protected $protectedDefaultVar = 'protected_laravel';
    public    $publicNoDefaultVar;
    public    $publicDefaultVar    = 'public_laravel';
    
    private function testPrivateGetClassMethod()
    {
    }
    
    protected function testProtectedGetClassMethod()
    {
    }
    
    public function testPublicGetClassMethod()
    {
    }
}

class ParentClass
{
    public function testGetCalledClass()
    {
        return get_called_class();
    }
}

class TestClassExists
{
    private   $testPrivatePropertyExists;
    protected $testProtectedPropertyExists;
    public    $testPublicPropertyExists;
    
    private function testPrivateMethodExists()
    {
    }
    
    protected function testProtectedMethodExists()
    {
    }
    
    public function testPublicMethodExists()
    {
    }
}

interface TestInterfaceExists
{
    
}

trait TestTraitExists
{
    
}

PHP不仅提供了检测class, interface, trait, property, method这些函数Introspection Functions，还提供了一整套的API即反射来检测class, interface, trait, property, method，这些API是好几个类组成的，提供了很多好用的方法。限于篇幅，下篇再聊下反射API。

总结：本文主要聊了下PHP提供的一套检测class, interface, trait, property, method的两个工具包：Introspection Functions和Reflection API，这里先聊到Introspection Functions。下篇再聊下Reflection API的使用，到时见。

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