create new object in php

问题

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.

回答1:

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();
}

回答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();
        }
    }

来源：https://stackoverflow.com/questions/19793586/create-new-object-in-php