blocks|key|951247|text|他们使用“反射”|type|unstyled|depth|inlineStyleRanges|entityRanges|data|951248|Symfony如何防止PHP抗议没有向构造函数提供足够的参数|blockquote|951249|反射允许您检查PHP中其他“事物”的定义。其中包括类--它们的方法，以及这些方法的参数。|951250|<?php
class+bar
{
++++//just+a+placeholder+class
};

$bar+=+new+bar();+//instance+of+bar

//class+to+inspect
class+foo
{++++++++
++++public+function+__construct(+bar+$bar)
++++{
++++++++//do+something+fancy+with+$bar
++++}++++++++
}

//get+the+Reflection+of+the+constructor+from+foo
$Method+=+new+ReflectionMethod('foo',+'__construct');

//get+the+parameters+(+I+call+them+arguments)
$Args+=+$Method->getParameters();

//get+the+first+argument
$Arg+=+reset($Args);

//export+the+argument+definition
$export+=+ReflectionParameter::export(
+++array(
++++++$Arg->getDeclaringClass()->name,+
++++++$Arg->getDeclaringFunction()->name
+++),+
+++$Arg->name,+
+++true
);

//parse+it+for+the+typehint
$type+=+preg_replace('/.*?(\w%2B)\s%2B\$'.$Arg->name.'.*/',+'\\1',+$export);
echo+"\nType:+$type\n\n";

var_dump(is_a($bar,+$type));|code-block|syntax|javascript|951251|产出：|951252|Type:+bar

bool(true)|951253|你可以看到它，这里|offset|length|951254|然后，您只需使用is_a()或其他什么来查看“输入”对象是否将bar作为其祖先之一。正如您在这个简化的例子中看到的，如果我们有对象$bar，我们就会知道它作为构造函数的输入非常好，因为它返回true。|style|CODE|951255|我应该指出，这可能不是问这个问题的合适地方，但我可以在我的许多项目中使用它，所以我不介意找出它。而且我从没用过交响乐..。对于解析类型提示的最后一段，特别要感谢这一问题：|951256|PHP反射-获取方法参数类型作为字符串|951257|也就是说，我大概在10秒内就算出了Regx，出口方法就没那么多了。|951258|这是它的文档的范围。|951259|http://php.net/manual/en/reflectionparameter.export.php|951260|字面意思|951261|public+static+string+ReflectionParameter::export+(+string+$function+,+string+$parameter+[,+bool+$return+]+)|951262|entityMap|0|LINK|mutability|MUTABLE|url|http://sandbox.onlinephpfunctions.com/code/d67c5fa2aeca1923cb93a716e37bc8cbc288bc9b|1|https://stackoverflow.com/questions/4513867/php-reflection-get-method-parameter-type-as-string|2^0|0|0|0|0|0|0|7|2|0|0|8|6|V|3|0|0|0|J|1|0|0|0|0|1J|2|0|0|0^^$0|@$1|2|3|4|5|6|7|1M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|1N|8|@]|9|@]|A|$]]|$1|E|3|F|5|6|7|1O|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|1P|8|@]|9|@]|A|$J|K]]|$1|L|3|M|5|6|7|1Q|8|@]|9|@]|A|$]]|$1|N|3|O|5|I|7|1R|8|@]|9|@]|A|$J|K]]|$1|P|3|Q|5|6|7|1S|8|@]|9|@$R|1T|S|1U|1|1V]]|A|$]]|$1|T|3|U|5|6|7|1W|8|@$R|1X|S|1Y|V|W]|$R|1Z|S|20|V|W]]|9|@]|A|$]]|$1|X|3|Y|5|6|7|21|8|@]|9|@]|A|$]]|$1|Z|3|10|5|6|7|22|8|@]|9|@$R|23|S|24|1|25]]|A|$]]|$1|11|3|12|5|6|7|26|8|@]|9|@]|A|$]]|$1|13|3|14|5|6|7|27|8|@]|9|@]|A|$]]|$1|15|3|16|5|6|7|28|8|@]|9|@$R|29|S|2A|1|2B]]|A|$]]|$1|17|3|18|5|6|7|2C|8|@]|9|@]|A|$]]|$1|19|3|1A|5|I|7|2D|8|@]|9|@]|A|$J|K]]|$1|1B|3|-4|5|6|7|2E|8|@]|9|@]|A|$]]]|1C|$1D|$5|1E|1F|1G|A|$1H|1I]]|1J|$5|1E|1F|1G|A|$1H|1K]]|1L|$5|1E|1F|1G|A|$1H|16]]]]

They use Refection

<blockquote>
 How can Symfony prevent PHP from protesting that not enough arguments were fed to the constructor
</blockquote>

Reflection allows you to inspect the definition of other "things" in PHP. Among them are Classes their methods, and the arguments for those methods.

<pre><code>&lt;?php
class bar
{
 //just a placeholder class
};

$bar = new bar(); //instance of bar

//class to inspect
class foo
{ 
 public function __construct( bar $bar)
 {
 //do something fancy with $bar
 } 
}

//get the Reflection of the constructor from foo
$Method = new ReflectionMethod('foo', '__construct');

//get the parameters ( I call them arguments)
$Args = $Method-&gt;getParameters();

//get the first argument
$Arg = reset($Args);

//export the argument definition
$export = ReflectionParameter::export(
 array(
 $Arg-&gt;getDeclaringClass()-&gt;name, 
 $Arg-&gt;getDeclaringFunction()-&gt;name
 ), 
 $Arg-&gt;name, 
 true
);

//parse it for the typehint
$type = preg_replace('/.*?(\w+)\s+\$'.$Arg-&gt;name.'.*/', '\\1', $export);
echo "\nType: $type\n\n";

var_dump(is_a($bar, $type));
</code></pre>

Outputs:

<pre><code>Type: bar

bool(true)
</code></pre>

You can see it <a href="http://sandbox.onlinephpfunctions.com/code/d67c5fa2aeca1923cb93a716e37bc8cbc288bc9b" rel="nofollow noreferrer">here</a>

Then you just use <code>is_a()</code> or whatever to see if an "input" object has <code>bar</code> as one of it's ancestors. And as you can see in this simplified example if we had object $bar, we would know that it's perfectly good as an input to our constructor because it returns true.

I should note SO is probably not the right place to ask this, but i could use it in one of my many projects so I didn't mind figuring it out. Also I never used Symphony...
Special thanks to this SO question for the last bit on parsing the type hint:

<a href="https://stackoverflow.com/questions/4513867/php-reflection-get-method-parameter-type-as-string">PHP Reflection - Get Method Parameter Type As String</a>

That said I would have figured the Regx out in about 10 seconds, the export method no so much. 

This is the extent of the documentation on it

<a href="http://php.net/manual/en/reflectionparameter.export.php" rel="nofollow noreferrer">http://php.net/manual/en/reflectionparameter.export.php</a>

Literally

<pre><code>public static string ReflectionParameter::export ( string $function , string $parameter [, bool $return ] )
</code></pre>

blocks|key|951294|text|正如其他人提到的，他们使用反射。如果您想了解Symfony到底是如何做到这一点的，请从autowire()方法这里开始|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|951295|entityMap|0|LINK|mutability|MUTABLE|url|http://php.net/manual/en/intro.reflection.php|1|https://github.com/symfony/symfony/blob/44fcbd34899755c4b7c8744df62021e51ab258ff/src/Symfony/Component/DependencyInjection/ContainerBuilder.php^0|17|A|D|2|0|1J|2|1|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@$9|S|A|T|1|U]|$9|V|A|W|1|X]]|E|$]]|$1|F|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]|N|$5|I|J|K|E|$L|O]]]]

As others mentioned, they use <a href="http://php.net/manual/en/intro.reflection.php" rel="nofollow noreferrer">Reflection</a>. If you want to see how exactly Symfony is doing this, start with <code>autowire()</code> method <a href="https://github.com/symfony/symfony/blob/44fcbd34899755c4b7c8744df62021e51ab258ff/src/Symfony/Component/DependencyInjection/ContainerBuilder.php" rel="nofollow noreferrer">here</a>

This is not about instructions (the docs are sufficient), but a question of how things work.

<a href="https://symfony.com/doc/current/service_container/autowiring.html#autowiring-logic-explained" rel="nofollow noreferrer">Symfony 4's autowiring system</a> allows us to auto-inject services by simply typehinting 

<pre><code>use App\Util\Rot13Transformer;

class TwitterClient
{
 public function __construct(Rot13Transformer $transformer)
 {
 $this-&gt;transformer = $transformer;
 }
}
</code></pre>

To gain a deeper understanding of PHP, I have looked around in the symfony-bundle source code but can't find the spot where the "magic" happens. 

How can Symfony prevent PHP from protesting that not enough arguments were fed to the constructor (or any function that uses autowiring)?

How does Symfony's autowiring work behind the scenes?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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这不是关于指令(文档是足够的)，而是一个事情是如何工作的问题。允许我们通过简单的键入提示来自动注入服务。use App\Util\Rot13Transformer;class TwitterClient{  public function __construct(Rot13Transformer $transforme...

问辛弗尼在幕后的自动工作是怎样的？
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