Question

i wanna store some configuration data in some objects, and i’ve a problem…

class B {
  const attr1 = 'something1';
  const attr2 = 'something2';
  const attr3 = 'something3';
}

class A {
  const attr1 = 'somethingA1';
  const attr2 = 'somethingA2';
  const attr3 = 'somethingA3';
  const b = <---- i wanna put here a reference of B, but B as a class (not an object...), i'm crazy?
}

I’m not sure if my example is clear… from A, i want to access to attr1 of B, like A::B::attr1, or something like this, there’s another way to do this? Or i’m wrong?

Answer 1

There is no way to assign reference to a Class, nor is there a way to assign class constants at runtime. So your entire approach is pretty much impossible. What you can do is

const b = 'B' 

and as of PHP 5.3.0 you could then do

$b = A::b;
echo $b::attr1;

but you cannot do A::b::attr1. This will raise a T_PAAMAYIM_NEKUDOTAYIM error. It’s a parser limitation. PHP cannot do this as of this writing.

---

Because the class B contains a group of data of A, i want to store in b (of A) a complex data, i want to do like this because i wanna keep the code clean

You can solve this easily by making B a composite of A, e.g. you either inject B into A when you create A

class A
{
    private $b;

    public function __construct(B $b)
    {
        $this->b = $b;
    }
}
$a = new A(new B);

or create B inside A, e.g.

class A
{
    private $b;

    public function __construct()
    {
        $this->b = new B;
    }
}

Because B is just the data parts of A, you tunnel all public access through A instead of getting hold of B and then using B’s methods. So any code using A does not need to know there is some B inside A. This will allow you to change B easily without needing to worry about code that consumes A, e.g. to get attr1 you add a getter to A:

public function getAttr1()
{
    $b = $this->b;
    return $b::attr1;
}

You can mitigate the clumsy need for assignment when using properties instead of constants in B (constants are stupid in PHP anyway as you have to treat them as public API), e.g.

class B
{ 
    private $attr1;

    public function getAttr1()
    {
        return $this->attr1;
    }
}

And then you can do in A:

public function getAttr1()
{
    return $this->b->getAttr1();
}

Even better would be not to expose the internals of B through A altogether though and only add public methods that do something with A. This will make your API much smaller and your code more OO.