如何在类变量和函数参数中使用变量变量

Question

This is what I want to do:

class Contacts {

    private $_plural = 'contacts';
    private $_single = 'contact';
    private $_factory = 'contactfactory';
    private $_model = 'contact_model';

    private $_idname = $_plural . "Id";

    function a($$_idname = 0) {

    }
}

These two lines:

private $_idname = $_plural . "Id";

and

function a ($$_idname = 0) {

aren't working. Why? And how can I fix this?

EDIT

About the function argument:

If $_idname = "contactId" I want the argument to be $contactId. That's why I have two dollar signs there. This might be not the correct way to handle this, but this is what I want to accomplish.

Answer 1

You could change

private $_idname = $_plural . "Id";

to

private $_idname;
public function __construct(){
  $this->_idname = $this->_plural.'Id';
}

first.

Not seeing enough in function a. Probably more like:

public function a($really = 'What is the point of those underscores?'){
  ${$this->_idname} = $really; // local $contacts var holds $really
}

I'm really guessing that you want to have a method that will automatically change your instantiated Object property. You don't need a variable variable for that. If you want to affect a variable which you are passing as an argument it's &$yourVar. There is no need to pass a property of an instantiated Object to its own method, since you already have access to it within the method with $this->yourVar.