关于PHP名称空间的几个问题

Question

I'm porting an existing project to namespaces and i ended up hitting some walls and the official documentation could not help me. Maybe you guys can! :)

1) How do i extend a class from a level above in the namespace? For example:

namespace MyProject\Exceptions;

abstract class Handler {

}

namespace MyProject\Exceptions\Handlers;

class Test extends \MyProject\Exceptions\Handler {

}

2) How do i use namespaces with functions that expect callbacks?

namespace MyProject;

class Main {
    public function __construct() {
        set_error_handler(array('MyProject', 'handleErrors'));
    }

    public function handleErrors() {
        echo "hi";
    }
}

Answer 1

Question 1: There is no shorthand for addressing the namespace "above" your current namespace. You have to use the full path, as you already did above.

Question 2: It is true that you can use anonymous functions (which were introduced in 5.3), and that may often be a good choice:

namespace MyProject;

class Main {
     public function __construct() {
         set_error_handler( function() { 
              echo "hi"; 
         } );
     }
}

However, it is not always better to use anonymous functions. Functions are a useful abstraction for the very reason that you can call them from different places. Anonymous functions are a shorthand for creating functions that are only needed once.

If you want to use a regular non-anonymous function, please note first that in your above example, you are using an instance method, so you must provide an instance with $this:

namespace MyProject;

class Main {
     public function __construct() {
         set_error_handler(array($this, 'handleErrors'));
     }

     public function handleErrors() {
         echo "hi";
     }
}

Additionally, there is the case where you want to address a static function from a namespaced class. In this case, the array syntax must include the class name. If the class name has a namespace, you should use the full namespace path as you would in your source code:

namespace MyProject;

class Main {
    public function __construct() {
        set_error_handler(array('MyProject\Main', 'handleErrors'));
    }

    public static function handleErrors() {
        echo "hi";
    }
}

Answer 2

Just like other namespace things. However, make sure to escape the backslashes!

-edit-

Since we're talking about "modern PHP" here, I strongly recommend simply passing a function as a callback rather than using your way of building a callback. Nowadays you can simply accept a function and use that as the callback, as you can do in other programming languages such as C++.

namespace Foo;
function Bar($callback) { $callback(); }

// Other file
Foo\Bar(function() {
    // Do something
});