Why can't we use the "new" keyword in a class property?

Question

Possible Duplicate:
Instance as a static class property

I got a problem about creating an Object in a class as an attribute.

include 'Bar.php';
class Foo()
{
    private $bar = new Bar();
}

It comes out a parse error. But when I put the $bar outsite class

include 'Bar.php';
class Foo()
{
    //private $bar = new Bar();
}
$bar = new Bar();

No syntax error. works perfectly. So what's the problem. I just ported my Java knowledge to PHP. Sometimes, its so confusing.

It's not possible; there is a long discussion on why, check it out:[Why don't PHP attributes allow functions?](http://stackoverflow.com/q/3960323) — Pekka, Feb 18 '12 at 10:55
more: http://stackoverflow.com/search?q=[php]+body%3A%22initialization+must+be+a+constant+value%22 — Gordon, Feb 18 '12 at 11:24
@Gordon the question linked above is the only thing close to a canonical explanation attempt. I know of no more; might just upvote your dupe-link so it becomes more visible in the close dialog... Do you think it's worth adding to the Tag Wiki? — Pekka, Feb 18 '12 at 11:28
@Pekka IMO the tag wiki is worthless because no one looks into it, but sure, go ahead and add it ;) Though I think it would make more sense to go through the search, hijack one question, rewrite it and have the good answers merged into it. — Gordon, Feb 18 '12 at 11:30
@Gordon will do. We should be able to close questions as a duplicate of the Tag Wiki. *That* would increase its visibility :) — Pekka, Feb 18 '12 at 11:31
@Pekka I'm still convinced it needs subpages (like Operator reference) — Gordon, Feb 18 '12 at 11:33

score 2 · Accepted Answer · edited Feb 18 '12 at 17:03

2

You have to put it into the constructor:

class Foo() {
    private $bar;
    function __construct() {
        $this->bar = new Bar();
    }
}

edited Feb 18 '12 at 17:03

Robert Harvey

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answered Feb 18 '12 at 10:55

Karoly Horvath

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Object property of an abstract/base class must be initialized in every constructor of every inherited class. Very annoying. – Dávid Horváth Nov 11 '14 at 19:16
1

Just call the parent constructor, and it will do the job... – Karoly Horvath Nov 11 '14 at 19:58
Nice, but it is easy to forget this. – Dávid Horváth Nov 12 '14 at 00:41

score 0 · Answer 2 · answered Feb 18 '12 at 10:58

class Foo {
    private $bar;

    public function __construct() {
      $this->bar = new Bar();
    }

    public function check() {
      return $this->bar->checkBack();
    }
}

class Bar {
  public function __construct() {
    print "good\n";
  }

  public function checkBack() {
    return "checked";
  }
}

$f = new Foo();
print $f->check();

Why can't we use the "new" keyword in a class property?

2 Answers2