CODEWITHSUNDEEP
phpoopinheritance
confused
confused

Reputation: 23

Extending classes in PHP - strange behaviour

First, quote from PHP manual (http://php.net/manual/en/keyword.extends.php):

The extended or derived class has all variables and functions of the
base class (this is called 'inheritance' despite the fact that nobody
died) and what you add in the extended definition.

So why is that this simple example doesn't work:

<?php

class A
{
    private function a() 
    { 
        echo 'a'; 
    }

    public function b() 
    { 
        echo 'b'; 
    }

}


class B extends A 
{
    //no extended definition, only what's inherited 
}

$object_B = new B();

echo $object_B->b(); // fatal error: Call to private A::a() from invalid context 
?>

After some experimenting, it turns out that removing method a from class A makes it work. And I'm not even calling it anywhere.

Upvotes: 2

Views: 114

Answers (4)

jonju
jonju

Reputation: 2736

Here's the clarification:

You are defining method a() in Class A. They have the same name so method a() is treated as constructor of Class A. Therefore, the moment you initialize Class B in $object_B = new B();, you initialize Class A too since A is extending B and the constructor method is called. Because Classes which have a constructor method call this method on each newly-created object PHP Constructor. and hence the error.

I believe this clarifies your doubt.

Upvotes: 0

Haresh Vidja
Haresh Vidja

Reputation: 8496

In class A you have define a() method it with same name of class. so it is constructor method of A class. but in PHP you can not make private constructor method. your code should be like this.

<?php
class A
{
    public function a() 
    { 
        echo 'a'; 
    }

    public function b() 
    { 
        echo 'b'; 
    }

}


class B extends A 
{
    //no extended definition, only what's inherited 
}

$object_B = new B();

echo $object_B->b();

Upvotes: 0

Davide Perozzi
Davide Perozzi

Reputation: 386

"Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP" - Reports PHP 7 after executing the sample code.

I think you can't name the method with the same name as the class. In older PHP-Versions you could define the constructor of the class by naming the method like the class. PHP assumes the functions a to be a constructor. So it won't work that way.

Like Zac Brown said, you have to use the __construct() method.

Upvotes: 0

Zac Brown
Zac Brown

Reputation: 436

You can use a method of the same name as a constructor with a PHP class. So, your method a is acting as a constructor for class A.

Rename your method, and it should work:

class First
{
    private function another() 
    { 
        echo 'a'; 
    }

    public function b() 
    { 
        echo 'b'; 
    }
}

See __construct() vs SameAsClassName() for constructor in PHP

Upvotes: 3

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