Laravel学习笔记之Callback Type

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;
    }
}

图片描述

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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