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up vote 3 down vote favorite

I am trying to use a variable in an array within my class

class MyClass {

public static $a = "World";

public static $b = array("Hello" => self::$a);

}

This code doesn't work. Should I be using MyClass::$a or something else. Any ideas?

share|improve this question
4  
Class properties can't contain expressions that have to be evaluated at runtime, and self::$a requires a runtime evaluation. If your $a isn't going to change, make it a constant –  Mark Baker Dec 29 '13 at 12:14
    
Initialize $b in the class constructor. –  Barmar Dec 29 '13 at 12:16
    
@Barmar, slightly awkward to initialize in the constructor as it's static –  Mark Baker Dec 29 '13 at 12:17
1  
Only slightly. if (!$b) { self::$b = array(...) }. –  Barmar Dec 29 '13 at 12:20
    
@Barmar - but that means instantiating the class, which shouldn't be a prerequisite for anything defined as static –  Mark Baker Dec 29 '13 at 12:22

3 Answers 3

up vote 3 down vote accepted

You probably can instatiate them at runtime:

class MyClass {
    public static $a;
    public static $b;
}

MyClass::$a = "World";
MyClass::$b = [ "Hello" => MyClass::$a ];

Or you can create a static initialization method:

class MyClass {
    public static $a;
    public static $b;

    public static function init(){
        static::$a = "World";
        static::$b = [ "Hello" => static::$a ];
    }
}

MyClass::init();
share|improve this answer
    
This is very good. It works on what @awlad-liton said, but this approach is more useful - thanks a lot! –  Jason Lipo Dec 29 '13 at 13:10
    
@JasonLipo glad to help. Good luck. –  HAL9000 Dec 29 '13 at 13:10
up vote 3 down vote

If your $a won't change, make it a constant

class MyClass {

    const a = "World";

    public static $b = array("Hello" => self::a);

}

var_dump(MyClass::$b);
share|improve this answer
    
Yes, this does work. However in the context I want to use it, I don't want $a to be a constant. –  Jason Lipo Dec 29 '13 at 12:36
    
In that case, if your properties still need to be static, @HAL9000 has provided your options. –  Mark Baker Dec 29 '13 at 12:37
up vote 1 down vote 
class MyClass {

    public static $a = "World";
    public static $b;
    public function __construct(){
      self::$b = array("Hello" => self::$a);
    }

}
$obj = new MyClass();
share|improve this answer
    
Yes I think that's the answer. I have to use a __construct function. Thanks a lot! –  Jason Lipo Dec 29 '13 at 12:37
    
Note that if you want $b to automatically reflect any changes made to $a, you'll need to set self::$a by reference –  Mark Baker Dec 29 '13 at 13:06
    
@Jason Lipo: You accepted my answer and after that someone edited his answer after acceptance you did change your acceptance also!! –  Awlad Liton Dec 29 '13 at 13:19
    
I changed the acceptance not because of the edit. I tried the static function approach from @HAL9000 and that proved to work the most simply. –  Jason Lipo Dec 29 '13 at 21:15

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