说明：本文主要学习PHP的回调类型callback type,通常在使用函数进行回调时，如使用call_user_func($callback, $parameters)进行回调时，需要传入回调callback，实际上有几种callback type的，在Laravel中也大量使用回调，并根据场景不同传入不同的回调类型。
开发环境：Laravel5.3 + PHP7
(Function/Static Class Method) Callback Type
Function Callback Type是把函数名作为callable类型传进去作为回调类型，形式如：($function_name, $dependency)。Static Class Method Callable Type与其类似，是把类名+静态方法名传进去作为回调类型，形式如：("$class_name::$static_method_name", $dependency)。看下PHPUnit测试，看看如何使用callback type，爆绿灯：
assertSame($expected, $actual); } public function testStaticClassMethodCallback() { // Arrange $expected = 'container'; // Actual $actual = call_user_func('MyRightCapital\Container\Tests\StaticClassMethodCallback::staticClassMethod', 'container'); // ("$class_name::$static_method_name", $dependency) // Assert $this->assertSame($expected, $actual); }}function functionCallback($app){ return $app;}class StaticClassMethodCallback{ public static function staticClassMethod($app) { return $app; }} (Class Method/Relation Class Method) Callback Type
Class Method Callback Type也是类名+静态方法名，只不过形式稍不一样，形式如：([$class_name, $method_name], $dependency)。Relation Class Method Callback Type是可以使用父类的方法传进去作为回调，形式如：([$class_name, "parent::$method_name"], $dependency)。写个PHPUnit测试看下使用：
public function testClassMethodCallback() { // Arrange $expected = 'container'; // Actual $actual = call_user_func([ClassMethodCallback::class, 'classMethod'], 'container'); // ([$class_name, $method_name], $dependency) // Assert $this->assertSame($expected, $actual); } public function testRelationClassMethodCallback() { // Arrange $expected = 'container/container'; // Actual $actual = call_user_func([ClassMethodCallback::class, 'parent::classMethod'], 'container'); // ([$class_name, "parent::$method_name"], $dependency) // Assert $this->assertSame($expected, $actual); } class ClassMethodCallback extends ParentClassMethodCallback { public static function classMethod($app) { return $app; } } class ParentClassMethodCallback { public static function classMethod($app) { return $app . '/' . $app; } } Object Method Callback Type
Object Method Callback Type是把对象方法作为参数传进去作为回调，形式如：([$object, $method_name], $dependency)，写个PHPUnit测试：
public function testObjectMethodCallback() { // Arrange $class_method_callback = new ClassMethodCallback(); $expected = 'container'; // Actual $actual = call_user_func([$class_method_callback, 'objectMethod'], 'container'); // ([$object, $method_name], $dependency) // Assert $this->assertSame($expected, $actual); } class ClassMethodCallback extends ParentClassMethodCallback { public static function classMethod($app) { return $app; } public function objectMethod($app) { return $app; } } Closure
把Closure作为参数传进去作为回调参数这种方式在Laravel中大量使用，比如Laravel的Pipeline源码就大量使用这种方式，Pipeline的源码可看：。写下PHPUnit测试看下：
public function testClosureCallback() { // Arrange // Actual $actual = call_user_func(getClosure(), 'stack', 'pipe'); $actual_value = call_user_func($actual, 'request'); // Assert $this->assertInstanceOf(\Closure::class, $actual); $this->assertSame('request/stack/pipe', $actual_value); } function getClosure() { return function ($stack, $pipe) { return function ($passable) use ($stack, $pipe) { return $passable . '/' . $stack . '/' . $pipe; }; }; } 最后，给出整个源码和测试结果：
assertSame($expected, $actual); } public function testStaticClassMethodCallback() { // Arrange $expected = 'container'; // Actual $actual = call_user_func('MyRightCapital\Container\Tests\StaticClassMethodCallback::staticClassMethod', 'container'); // ("$class_name::$static_method_name", $dependency) // Assert $this->assertSame($expected, $actual); } public function testClassMethodCallback() { // Arrange $expected = 'container'; // Actual $actual = call_user_func([ClassMethodCallback::class, 'classMethod'], 'container'); // ([$class_name, $method_name], $dependency) // Assert $this->assertSame($expected, $actual); } public function testRelationClassMethodCallback() { // Arrange $expected = 'container/container'; // Actual $actual = call_user_func([ClassMethodCallback::class, 'parent::classMethod'], 'container'); // ([$class_name, "parent::$method_name"], $dependency) // Assert $this->assertSame($expected, $actual); } public function testObjectMethodCallback() { // Arrange $class_method_callback = new ClassMethodCallback(); $expected = 'container'; // Actual $actual = call_user_func([$class_method_callback, 'objectMethod'], 'container'); // ([$object, $method_name], $dependency) // Assert $this->assertSame($expected, $actual); } public function testClosureCallback() { // Arrange // Actual $actual = call_user_func(getClosure(), 'stack', 'pipe'); $actual_value = call_user_func($actual, 'request'); // Assert $this->assertInstanceOf(\Closure::class, $actual); $this->assertSame('request/stack/pipe', $actual_value); }}function getClosure(){ return function ($stack, $pipe) { return function ($passable) use ($stack, $pipe) { return $passable . '/' . $stack . '/' . $pipe; }; };}function functionCallback($app){ return $app;}class StaticClassMethodCallback{ public static function staticClassMethod($app) { return $app; }}class ClassMethodCallback extends ParentClassMethodCallback{ public static function classMethod($app) { return $app; } public function objectMethod($app) { return $app; }}class ParentClassMethodCallback{ public static function classMethod($app) { return $app . '/' . $app; }} 
总结：本文主要总结下PHP的Callback Type，便于提高自己的代码设计能力。遇到好的技术再聊，到时见。
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