Laravel 核心——服務容器的細節特性

leoyang發表於2017-05-28

Laravel

前言

本文 GitBook 地址： https://www.gitbook.com/book/leoyang90/laravel-source-analysis
首先歡迎關注我的部落格： www.leoyang90.cn

在前面幾個部落格中，我詳細講了 Ioc 容器各個功能的使用、繫結的原始碼、解析的原始碼，今天這篇部落格會詳細介紹 Ioc 容器的一些細節，一些特性，以便更好地掌握容器的功能。

注：本文使用的測試類與測試物件都取自 laravel 的單元測試檔案src/illuminate/tests/Container/ContainerTest.php

rebind繫結特性

rebind 在繫結之前

instance 和普通 bind 繫結一樣，當重新繫結的時候都會呼叫 rebind 回撥函式，但是有趣的是，對於普通 bind 繫結來說，rebind 回撥函式被呼叫的條件是當前介面被解析過：

public function testReboundListeners()
{
    unset($_SERVER['__test.rebind']);

    $container = new Container;
    $container->rebinding('foo', function () {
        $_SERVER['__test.rebind'] = true;
    });
    $container->bind('foo', function () {
    });
    $container->make('foo');
    $container->bind('foo', function () {
    });

    $this->assertTrue($_SERVER['__test.rebind']);
}

所以遇到下面這樣的情況,rebinding 的回撥函式是不會呼叫的：

public function testReboundListeners()
{
    unset($_SERVER['__test.rebind']);

    $container = new Container;
    $container->rebinding('foo', function () {
        $_SERVER['__test.rebind'] = true;
    });
    $container->bind('foo', function () {
    });
    $container->bind('foo', function () {
    });

    $this->assertFalse(isset($_SERVER['__test.rebind']));
}

有趣的是對於 instance 繫結：

public function testReboundListeners()
{
    unset($_SERVER['__test.rebind']);

    $container = new Container;
    $container->rebinding('foo', function () {
        $_SERVER['__test.rebind'] = true;
    });
    $container->bind('foo', function () {
    });
    $container->instance('foo', function () {
    });

    $this->assertTrue(isset($_SERVER['__test.rebind']));
}

rebinding 回撥函式卻是可以被呼叫的。其實原因就是 instance 原始碼中 rebinding 回撥函式呼叫的條件是 rebound 為真，而普通 bind 函式呼叫 rebinding 回撥函式的條件是 resolved 為真. 目前筆者不是很清楚為什麼要對 instance 和 bind 區別對待，希望有大牛指導。

rebind 在繫結之後

為了使得 rebind 回撥函式在下一次的繫結中被啟用，在 rebind 函式的原始碼中，如果判斷當前物件已經繫結過，那麼將會立即解析：

public function rebinding($abstract, Closure $callback)
{
    $this->reboundCallbacks[$abstract = $this->getAlias($abstract)][] = $callback;

    if ($this->bound($abstract)) {
        return $this->make($abstract);
    }
}

單元測試程式碼：

public function testReboundListeners1()
{
    unset($_SERVER['__test.rebind']);

    $container = new Container;
    $container->bind('foo', function () {
        return 'foo';
    });

    $container->resolving('foo', function () {
        $_SERVER['__test.rebind'] = true;
    });

    $container->rebinding('foo', function ($container,$object) {//會立即解析
        $container['foobar'] = $object.'bar';
    });

    $this->assertTrue($_SERVER['__test.rebind']);

    $container->bind('foo', function () {
    });

    $this->assertEquals('bar', $container['foobar']);
}

resolving 特性

resolving 回撥的型別

resolving 不僅可以針對介面執行回撥函式，還可以針對介面實現的型別進行回撥函式。

public function testResolvingCallbacksAreCalledForType()
{
    $container = new Container;
    $container->resolving('StdClass', function ($object) {
        return $object->name = 'taylor';
    });
    $container->bind('foo', function () {
          return new StdClass;
    });
    $instance = $container->make('foo');

    $this->assertEquals('taylor', $instance->name);
}
public function testResolvingCallbacksShouldBeFiredWhenCalledWithAliases()
{
    $container = new Container;
    $container->alias('StdClass', 'std');
    $container->resolving('std', function ($object) {
        return $object->name = 'taylor';
    });
    $container->bind('foo', function () {
        return new StdClass;
    });
    $instance = $container->make('foo');

    $this->assertEquals('taylor', $instance->name);
}

resolving 回撥與 instance

前面講過，對於 singleton 繫結來說，resolving 回撥函式僅僅執行一次，只在 singleton 第一次解析的時候才會呼叫。如果我們利用 instance 直接繫結類的物件，不需要解析，那麼 resolving 回撥函式將不會被呼叫：

public function testResolvingCallbacksAreCalledForSpecificAbstracts()
{
    $container = new Container;
    $container->resolving('foo', function ($object) {
        return $object->name = 'taylor';
    });
    $obj = new StdClass;
    $container->instance('foo', $obj);
    $instance = $container->make('foo');

    $this->assertFalse(isset($instance->name));
}

extend 擴充套件特性

extend 用於擴充套件繫結物件的功能，對於普通繫結來說，這個函式的位置很靈活：

在繫結前擴充套件

public function testExtendIsLazyInitialized()
{
    ContainerLazyExtendStub::$initialized = false;

    $container = new Container;      
    $container->extend('Illuminate\Tests\Container\ContainerLazyExtendStub', function ($obj, $container) {
        $obj->init();
        return $obj;   
    });    
    $container->bind('Illuminate\Tests\Container\ContainerLazyExtendStub'); 

    $this->assertFalse(ContainerLazyExtendStub::$initialized);   
    $container->make('Illuminate\Tests\Container\ContainerLazyExtendStub');   
    $this->assertTrue(ContainerLazyExtendStub::$initialized);
}

在繫結後解析前擴充套件

public function testExtendIsLazyInitialized()
{
    ContainerLazyExtendStub::$initialized = false;

    $container = new Container;   
    $container->bind('Illuminate\Tests\Container\ContainerLazyExtendStub');    
    $container->extend('Illuminate\Tests\Container\ContainerLazyExtendStub', function ($obj, $container) {
        $obj->init();
        return $obj;   
    });    

    $this->assertFalse(ContainerLazyExtendStub::$initialized);   
    $container->make('Illuminate\Tests\Container\ContainerLazyExtendStub');   
    $this->assertTrue(ContainerLazyExtendStub::$initialized);
}

在解析後擴充套件

public function testExtendIsLazyInitialized()
{
    ContainerLazyExtendStub::$initialized = false;

    $container = new Container;   
    $container->bind('Illuminate\Tests\Container\ContainerLazyExtendStub');         

    $container->make('Illuminate\Tests\Container\ContainerLazyExtendStub'); 
    $this->assertFalse(ContainerLazyExtendStub::$initialized);

    $container->extend('Illuminate\Tests\Container\ContainerLazyExtendStub', function ($obj, $container) {
        $obj->init();
        return $obj;   
    });
    $this->assertFalse(ContainerLazyExtendStub::$initialized);  

    $container->make('Illuminate\Tests\Container\ContainerLazyExtendStub'); 
    $this->assertTrue(ContainerLazyExtendStub::$initialized);
}

可以看出，無論在哪個位置，extend 擴充套件都有 lazy 初始化的特點，也就是使用 extend 函式並不會立即起作用，而是要等到 make 解析才會啟用。

extend 與 instance 繫結

對於 instance 繫結來說，暫時 extend 的位置需要位於 instance 之後才會起作用，並且會立即起作用，沒有 lazy 的特點：

public function testExtendInstancesArePreserved()
{
    $container = new Container;

    $obj = new StdClass;
    $obj->foo = 'foo';
    $container->instance('foo', $obj);
    $container->extend('foo', function ($obj, $container) {
        $obj->bar = 'baz';

        return $obj;
    });

    $this->assertEquals('foo', $container->make('foo')->foo);
    $this->assertEquals('baz', $container->make('foo')->bar);
}

extend 繫結與 rebind 回撥

無論擴充套件物件是 instance 繫結還是 bind 繫結，extend 都會啟動 rebind 回撥函式：

public function testExtendReBindingInstance()
{
    $_SERVER['_test_rebind'] = false;

    $container = new Container;
    $container->rebinding('foo',function (){
        $_SERVER['_test_rebind'] = true;
    });

    $obj = new StdClass;
    $container->instance('foo',$obj);

    $container->make('foo');

    $container->extend('foo', function ($obj, $container) {
        return $obj;
    });

    this->assertTrue($_SERVER['_test_rebind']);
}

public function testExtendReBinding()
{
    $_SERVER['_test_rebind'] = false;

    $container = new Container;
    $container->rebinding('foo',function (){
        $_SERVER['_test_rebind'] = true;
    });
    $container->bind('foo',function (){
        $obj = new StdClass;

        return $obj;
    });

    $container->make('foo');

    $container->extend('foo', function ($obj, $container) {
        return $obj;
    });

    this->assertFalse($_SERVER['_test_rebind']);
}

contextual 繫結特性

contextual 在繫結前

contextual 繫結不僅可以與 bind 繫結合作，相互不干擾，還可以與 instance 繫結相互合作。而且 instance 的位置也很靈活，可以在 contextual 繫結前，也可以在contextual 繫結後：

public function testContextualBindingWorksForExistingInstancedBindings()
{
    $container = new Container;

    $container->instance('Illuminate\Tests\Container\IContainerContractStub', new ContainerImplementationStub);

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectOne')->needs('Illuminate\Tests\Container\IContainerContractStub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $this->assertInstanceOf(
             'Illuminate\Tests\Container\ContainerImplementationStubTwo',
             $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
     );
}

contextual 在繫結後

public function testContextualBindingWorksForNewlyInstancedBindings()
{
    $container = new Container;

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectOne')->needs('Illuminate\Tests\Container\IContainerContractStub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $container->instance('Illuminate\Tests\Container\IContainerContractStub', new ContainerImplementationStub);

    $this->assertInstanceOf(
            'Illuminate\Tests\Container\ContainerImplementationStubTwo',
        $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
    );
}

contextual 繫結與別名

contextual 繫結也可以在別名上進行，無論賦予別名的位置是 contextual 的前面還是後面：

public function testContextualBindingDoesntOverrideNonContextualResolution()
{
    $container = new Container;

    $container->instance('stub', new ContainerImplementationStub);
    $container->alias('stub', 'Illuminate\Tests\Container\IContainerContractStub');

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectTwo')->needs('Illuminate\Tests\Container\IContainerContractStub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $this->assertInstanceOf(
            'Illuminate\Tests\Container\ContainerImplementationStubTwo',
            $container->make('Illuminate\Tests\Container\ContainerTestContextInjectTwo')->impl
        );

    $this->assertInstanceOf(
            'Illuminate\Tests\Container\ContainerImplementationStub',
            $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
    );
}

public function testContextualBindingWorksOnNewAliasedBindings()
{
    $container = new Container;

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectOne')->needs('Illuminate\Tests\Container\IContainerContractStub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $container->bind('stub', ContainerImplementationStub::class);
    $container->alias('stub', 'Illuminate\Tests\Container\IContainerContractStub');

    $this->assertInstanceOf(
          'Illuminate\Tests\Container\ContainerImplementationStubTwo',
          $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
    );
}

爭議

目前比較有爭議的是下面的情況：

public function testContextualBindingWorksOnExistingAliasedInstances()
{
    $container = new Container;

    $container->alias('Illuminate\Tests\Container\IContainerContractStub', 'stub');
    $container->instance('stub', new ContainerImplementationStub);

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectOne')->needs('stub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $this->assertInstanceOf(
        'Illuminate\Tests\Container\ContainerImplementationStubTwo',
        $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
    ); 
}

由於instance的特性，當別名被繫結到其他物件上時，別名 stub 已經失去了與 Illuminate\Tests\Container\IContainerContractStub 之間的關係，因此不能使用 stub 代替作上下文繫結。
但是另一方面：

public function testContextualBindingWorksOnBoundAlias()
{
    $container = new Container;

    $container->alias('Illuminate\Tests\Container\IContainerContractStub', 'stub');
    $container->bind('stub', ContainerImplementationStub::class);

    $container->when('Illuminate\Tests\Container\ContainerTestContextInjectOne')->needs('stub')->give('Illuminate\Tests\Container\ContainerImplementationStubTwo');

    $this->assertInstanceOf(
        'Illuminate\Tests\Container\ContainerImplementationStubTwo',
        $container->make('Illuminate\Tests\Container\ContainerTestContextInjectOne')->impl
    ); 
}

程式碼只是從 instance 繫結改為 bind 繫結，由於 bind 繫結只切斷了別名中的 alias 陣列的聯絡，並沒有斷絕abstractAlias陣列的聯絡，因此這段程式碼卻可以通過，很讓人難以理解。本人在給 Taylor Otwell 提出 PR 時，作者原話為“I'm not making any of these changes to the container on a patch release.”。也許，在以後(5.5或以後)版本作者會更新這裡的邏輯，我們就可以看看服務容器對別名繫結的態度了，大家也最好不要這樣用。

服務容器中的閉包函式引數

服務容器中很多函式都有閉包函式，這些閉包函式可以放入特定的引數，在繫結或者解析過程中，這些引數會被服務容器自動帶入各種類物件或者服務容器例項。

bind 閉包引數

public function testAliasesWithArrayOfParameters()
{
    $container = new Container;    
    $container->bind('foo', function ($app, $config) {
        return $config;    
    });    

    $container->alias('foo', 'baz');    
    $this->assertEquals([1, 2, 3], $container->makeWith('baz', [1, 2, 3]));
}

extend 閉包引數

public function testExtendedBindings()
{
    $container = new Container;    
    $container['foo'] = 'foo’;    
    $container->extend('foo', function ($old, $container) {
        return $old.'bar’;    
    });

    $this->assertEquals('foobar', $container->make('foo'));

    $container = new Container;

    $container->singleton('foo', function () {
        return (object) ['name' => 'taylor'];    
    });    
    $container->extend('foo', function ($old, $container) {
        $old->age = 26;
        return $old;    
    });

    $result = $container->make('foo');
    $this->assertEquals('taylor', $result->name);    
    $this->assertEquals(26, $result->age);   
    $this->assertSame($result, $container->make('foo'));
}

bindmethod 閉包引數

public function testCallWithBoundMethod()
{
    $container = new Container;
    $container->bindMethod('Illuminate\Tests\Container\ContainerTestCallStub@unresolvable', function ($stub,$container) {
        $container['foo'] = 'foo';
        return $stub->unresolvable('foo', 'bar');
    });
    $result = $container->call('Illuminate\Tests\Container\ContainerTestCallStub@unresolvable');
    $this->assertEquals(['foo', 'bar'], $result);
    $this->assertEquals('foo',$container['foo']);
}

resolve 閉包引數

public function testResolvingCallbacksAreCalledForSpecificAbstracts()
{
     $container = new Container;
     $container->resolving('foo', function ($object，$container) {
         return $object->name = 'taylor';
     });

     $container->bind('foo', function () {
        return new StdClass;
     });
     $instance = $container->make('foo');

     $this->assertEquals('taylor', $instance->name);
}

rebinding 閉包引數

public function testReboundListeners()
{
    $container = new Container;
    $container->bind('foo', function () {
        return 'foo';
    });

    $container->rebinding('foo', function ($container,$object) {
         $container['bar'] = $object.'bar';
    });

    $container->bind('foo', function () {
    });

    $this->assertEquals('bar',$container['foobar']);
}

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