accessing private variable from member function in

问题:

I have derived a class from Exception, basically like so:

class MyException extends Exception {

    private $_type;

    public function type() {
        return $this->_type; //line 74
    }

    public function __toString() {

        include "sometemplate.php";
        return "";

    }

}

Then, I derived from MyException like so:

class SpecialException extends MyException {

    private $_type = "superspecial";

}

If I throw new SpecialException("bla") from a function, catch it, and go echo $e, then the __toString function should load a template, display that, and then not actually return anything to echo.

This is basically what's in the template file

<div class="<?php echo $this->type(); ?>class">

    <p> <?php echo $this->message; ?> </p>

</div>

in my mind, this should definitely work. However, I get the following error when an exception is thrown and I try to display it:

Fatal error: Cannot access private property SpecialException::$_type in C:\path\to\exceptions.php on line 74

Can anyone explain why I am breaking the rules here? Am I doing something horribly witty with this code? Is there a much more idiomatic way to handle this situation? The point of the $_type variable is (as shown) that I want a different div class to be used depending on the type of exception caught.

回答1:

Name the variable protected:

* Public: anyone either inside the class or outside can access them
* Private: only the specified class can access them. Even subclasses will be denied access.
* Protected: only the specified class and subclasses can access them

回答2:

just an example how to access private property

<?php
class foo {
    private $bar = 'secret';
}
$obj = new foo;


if (version_compare(PHP_VERSION, '5.3.0') >= 0)
{

      $myClassReflection = new ReflectionClass(get_class($obj));
      $secret = $myClassReflection->getProperty('bar');
      $secret->setAccessible(true);
      echo $secret->getValue($obj);
}
else 
{
    $propname="\0foo\0bar";
    $a = (array) $obj;
    echo $a[$propname];
}

回答3:

See my answer here: https://stackoverflow.com/a/40441769/1889685

---

As of PHP 5.4, you can use the predefined Closure class to bind a method/property of a class to a delta functions that has access even to private members.

The Closure class

For example we have a class with a private variable and we want to access it outside the class:

class Foo {
    private $bar = "Foo::Bar";
}

PHP 5.4+

$foo = new Foo;
$getFooBarCallback = function() {
    return $this->bar;
};

$getFooBar = $getFooBarCallback->bindTo($foo, 'Foo');
echo $getFooBar(); // Prints Foo::Bar

As of PHP 7, you can use the new Closure::call method, to bind any method/property of an obect to a callback function, even for private members:

PHP 7+

$foo = new Foo;
$getFooBar = function() {
    return $this->bar;
}

echo $getFooBar->call($foo); // Prints Foo::Bar

回答4:

You need to set the access to protected. Private means that it can only be accessed from within it's own class and can't be inherited. Protected allows it to be inhherited but it still can't be accessed directly from outside the class.

回答5:

If you check the visibility documentation, buried in a comment is:

// We can redeclare the public and protected method, but not private

You should make it protected to do what you're trying to do.

Incidentally, it looks like you're just setting it to be the class name - you could just use get_class():

<div class="<?php echo get_class($this); ?>class">

回答6:

You should indeed change the accessmodifier to protected when you'e builing inheritance classes.

One extra point though; don't use return ""; but just use return;