create new object in php

Question

I understand that PHP doesn't allow me to create a new instance of ClassB inside my ClassA, if the creation is not inside the scope of a function. Or I just don't understand...

class ClassA {

const ASD = 0;
protected $_asd = array();
//and so on

protected $_myVar = new ClassB(); // here I get *syntax error, unexpected 'new'* underlining 'new'

// functions and so on
}

Do I need some kind of constructor, or is there a way to actually create the object instance in a free way as I desire, as I am used to do in Java or C#. Or is using Singleton the only closest solution to my approach?

P.S. ClassB is located in the same package and folder as ClassA.

@sal00m - good question. I updated my post. Look at the P.S.. :) — Syspect
– Syspect, Commented Nov 5, 2013 at 16:19
RTFM: php.net/manual/en/language.oop5.properties.php class attributes can be intialized with constant values only. Expression results are expressly forbidden. You need to do what you want in the classA constructor. — Marc B
– Marc B, Commented Nov 5, 2013 at 16:20

Jason McCreary · Accepted Answer · 2013-11-05 16:17:44Z

4

According to the PHP docs:

declaration may include an initialization, but this initialization must be a constant value--that is, it must be able to be evaluated at compile time and must not depend on run-time information in order to be evaluated.

As such, you will need to instantiate $_myVar in your constructor:

protected $_myVar;    

public function __contruct() {
   $this->_myVar = new ClassB();
}

answered Nov 5, 2013 at 16:17

Jason McCreary

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4 Comments

Syspect Over a year ago

So I guess this object is created at compile time and I can use it in the rest of the class simply as $_myVar->someFunctionFromClassB(), is that correct?

Jason McCreary Over a year ago

Yes, don't forget the this prefix, of course: $this->_myVar->someFunctionFromClassB()

Syspect Over a year ago

@JasonMcCreary - good tip! Old habits from Java die hard... I have to get used to the PHP syntax.

Jason McCreary Over a year ago

You should read the docs as an introduction. Then reread them after you write some code :)

Marius · Accepted Answer · 2013-11-05 16:18:38Z

2

Yes, there is a constructor (see below)

class ClassA {

    const ASD = 0;
    protected $_asd = array();
    //and so on

    protected $_myVar; // initialization not allowed directly here

        public function __contruct() {
            $this->_myVar = new ClassB();
        }
    }

edited Nov 5, 2013 at 16:18

Marius

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answered Nov 5, 2013 at 16:17

JNDPNT

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