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：
<?php
namespace MyRightCapital\Container\Tests;
class Callback extends \PHPUnit_Framework_TestCase
{
public function testFunctionCallback()
{
// Arrange
$expected = 'container';
// Actual
$actual = call_user_func('MyRightCapital\Container\Tests\functionCallback', 'container'); // ($function_name, $dependency)
// Assert
$this->assertSame($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：Laravel学习笔记之Middleware源码解析。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：
<?php
namespace MyRightCapital\Container\Tests;
class Callback extends \PHPUnit_Framework_TestCase
{
public function testFunctionCallback()
{
// Arrange
$expected = 'container';
// Actual
$actual = call_user_func('MyRightCapital\Container\Tests\functionCallback', 'container'); // ($function_name, $dependency)
// Assert
$this->assertSame($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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