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Date: Thu, 02 Jul 2009 10:05:28 -0500
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To: troels knak-nielsen <troelskn@gmail.com>
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Subject: Re: [PHP-DEV] constructors are callable as regular functions.
From: greg@chiaraquartet.net (Greg Beaver)

troels knak-nielsen wrote:
> On Thu, Jul 2, 2009 at 4:47 PM, Edward Z. Yang<ezyang@mit.edu> wrote:
>> Excerpts from troels knak-nielsen's message of Thu Jul 02 10:14:18 -0400 2009:
>>> I would have expected the second call to __construct() to yield an error.
>> Why should it? Especially since this is idiomatic code:
>>
>> class A {
>>  public function __construct($a) {
>>    $this->a = $a;
>>  }
>> }
>>
>> class B extends A {
>>  public function __construct($a, $b) {
>>    $this->b = $b;
>>    parent::__construct($a);
>>  }
>> }
> 
> In that example, the object instance is not initialised when
> parent::__construct() is called.
> 
>> __construct doesn't do anything like allocate memory. It just happens
>> to get called when we do "new B(1, 2)"
> 
> I understand that. It's not a technical issue - It's more a matter of
> language semantics. Constructors are used for initializing state on an
> object. Basically, this behaviour makes it impossible to implement
> immutable objects in php. It's not a huge deal - I don't remember ever
> seen __construct() called directly.
> 
> --
> troels

Hi,

__construct can be private or protected, it just requires implementing a
factory() or singleton() method to retrieve the immutable object.

Greg