php 如何调用作为类变量的闭包？

How to call a closure that is a class variable?

提问by rsk82

class MyClass {
  var $lambda;
  function __construct() {
    $this->lambda = function() {echo 'hello world';};
    // no errors here, so I assume that this is legal
  }
}

$myInstance = new MyClass();
$myInstance->lambda();
//Fatal error: Call to undefined method MyClass::lambda()

So what is the correct syntax for reaching class variables ?

那么达到类变量的正确语法是什么？

回答by Arnaud Le Blanc

In PHP, methods and properties are in a separate namespace (you can have a method and a property with the same name), and whether you are accessing a property or a method depends of the syntax you are using to do so.

在 PHP 中，方法和属性位于单独的命名空间中（您可以拥有同名的方法和属性），并且您是访问属性还是方法取决于您使用的语法。

$expr->something()is a method call, so PHP will search somethingin the class' list of methods.

$expr->something()是一个方法调用，所以 PHP 将something在类的方法列表中搜索。

$expr->somethingis a property fetch, so PHP will search somethingin the class' list of properties.

$expr->something是一个属性获取，所以 PHP 将something在类的属性列表中搜索。

$myInstance->lambda();is parsed as a method call, so PHP searches for a method named lambdain your class, but there is no such method (hence the Call to undefined methoderror).

$myInstance->lambda();被解析为方法调用，因此 PHP 搜索lambda在您的类中命名的方法，但没有这样的方法（因此调用未定义的方法错误）。

So you have to use the fetch propertysyntax to fetch the lambda, and then call it.

所以你必须使用fetch 属性语法来获取 lambda，然后调用它。

• Since PHP 7.0, you can do this with ($obj->lambda)():

  ($obj->lambda)();
  

  The parentheses make sure that PHP parses ($obj->lambda)as fetch the property named lambda. Then, ()calls the result of fetching the property.

• or you can do this with ->lambda->__invoke():

  $myInstance = new MyClass();
  $myInstance->lambda->__invoke();
  

  __invokeis one of PHP's magic methods. When an object implements this method, it becomes invokable: it can be called using the $var()syntax. Anonymous functions are instances of Closure, which implements __invoke.

• Or assign it to a local variable:

  $lambda = $myInstance->lambda;
  $lambda();
  

• Or call it using call_user_func:

  call_user_func($myInstance->lambda);
  

  call_user_funccan call any callable, including anonymous functions.

• Alternatively, if this is a common pattern in your code, you can setup a __callmethod to forward calls to your lambda:

  class MyClass
  {
      private $lambda;
  
      public function __construct()
      {
          $this->lambda = function() {
              echo "Hello world!\n";
          };
      }
  
      public function __call($name, $args)
      {
          return call_user_func_array($this->$name, $args);
      }
  }
  

  Now this works:

  $myInstance = new MyClass();
  $myInstance->lambda();
  

  Since PHP 5.4 you can even do that in a trait:

  trait LambdasAsMethods
  {
      public function __call($name, $args)
      {
          return call_user_func_array($this->$name, $args);
      }
  }
  
  class MyClass
  {
      use LambdasAsMethods;
  
      private $lambda;
  
      public function __construct()
      {
          $this->lambda = function() {
              echo "Hello World!\n";
          };
      }
  }
  
  $myInstance = new MyClass();
  $myInstance->lambda();
  

• 从 PHP 7.0 开始，您可以使用以下命令执行此操作($obj->lambda)()：

  ($obj->lambda)();
  

  括号确保 PHP 解析($obj->lambda)为获取名为 lambda 的属性。然后，()调用获取属性的结果。

• 或者你可以这样做->lambda->__invoke()：

  $myInstance = new MyClass();
  $myInstance->lambda->__invoke();
  

  __invoke是PHP 的神奇方法之一。当一个对象实现这个方法时，它变得可调用：它可以使用$var()语法调用。匿名函数是 的实例Closure，它实现__invoke.

• 或者将其分配给局部变量：

  $lambda = $myInstance->lambda;
  $lambda();
  

• 或者使用 call_user_func 调用它：

  call_user_func($myInstance->lambda);
  

  call_user_func可以调用 any callable，包括匿名函数。

• 或者，如果这是您代码中的常见模式，您可以设置一个__call方法来将调用转发到您的 lambda：

  class MyClass
  {
      private $lambda;
  
      public function __construct()
      {
          $this->lambda = function() {
              echo "Hello world!\n";
          };
      }
  
      public function __call($name, $args)
      {
          return call_user_func_array($this->$name, $args);
      }
  }
  

  现在这有效：

  $myInstance = new MyClass();
  $myInstance->lambda();
  

  从 PHP 5.4 开始，您甚至可以在 trait 中做到这一点：

  trait LambdasAsMethods
  {
      public function __call($name, $args)
      {
          return call_user_func_array($this->$name, $args);
      }
  }
  
  class MyClass
  {
      use LambdasAsMethods;
  
      private $lambda;
  
      public function __construct()
      {
          $this->lambda = function() {
              echo "Hello World!\n";
          };
      }
  }
  
  $myInstance = new MyClass();
  $myInstance->lambda();
  

回答by akDeveloper

You can also call your lambda function without change something in your class, using ReflectionFunction.

您还可以使用 ReflectionFunction 调用 lambda 函数，而无需更改类中的某些内容。

$myInstance = new MyClass();
$lambda = new ReflectionFunction($myInstance->lambda);
$lambda->invoke();

or if you have to pass arguments then

或者如果你必须传递参数，那么

$args = array('arg'=>'value');
$lambda->invokeArgs($args);