PHP属性访问和美元符号

Question

I have been stepping up my PHP game lately. Coming from JavaScript, I've found the object model to be a little simpler to understand.

I've run into a few quirks that I wanted some clarifying on that I can't seem to find in the documentation.

When defining classes in PHP, you can define properties like so:

class myClass {

    public $myProp = "myProp";
    static $anotherProp = "anotherProp";

}

With the public variable of $myProp we can access it using (assuming myClass is referenced in a variable called $myClass) $myClass->myProp without the use of the dollar sign.

We can only access static variables using ::. So, we can access the static variable like $myClass::$anotherProp with a dollar sign.

Question is, why do we have to use dollar sign with :: and not ->??

EDIT

This is code I would assume would work (and does):

class SethensClass {

    static public $SethensProp = "This is my prop!";

}

$myClass = new SethensClass;
echo $myClass::$SethensProp;

Answer 1

A class constant is accessed with the :: scope operator, and no dollar sign, so the $ is needed there to differentiate between static class properties and class constants.

class myClass {
  public static $staticProp = "static property";

  const CLASS_CONSTANT = 'a constant';
}

echo myClass::CLASS_CONSTANT;
echo myClass::$staticProp;

So to access a variable, the $ is necessary. But the $ cannot be placed at the beginning of the class name like $myClass::staticProp because then the class name could not be identified by the parser, since it is also possible to use a variable as the class name. It must therefore be attached to the property.

$myClass = "SomeClassName";
// This attempts to access a constant called staticProp
// in a class called "SomeClassName"
echo $myClass::staticProp;

// Really, we need
echo myClass::$staticProp;