Referencing class function variables in php - php

Question

I've been looking over the PHP variable scope reference page and I can't seem to find a clear answer. I'm working with this basic model where I want to call a class function and have all of its variables accessible outside the class. I want to avoid using the global declaration as well and do this in the most efficient way possible.
class my_class() {
function my_class_function() {
$my_class_function_variable = 'juice';
return $my_class_function_variable;
}
}
$class_instance = new my_class();
function display_juice() {
$class_instance::my_class_function();
$my_class_function_variable;
}
Is there a quick answer in what I'm missing? I'm not getting any output or errors.
EDIT
I'm getting a syntax error when I declare the following within the class but not within the function.
public $current_user = wp_get_current_user();
Parse error: syntax error, unexpected '(', expecting ',' or ';'

Answer 1

You can access all setted variables in class if they are public.
And you can access any of its function if its again public...
Here is example . I have default value 'mydefault'.
I use it, then I change it and again I use it..
class my_class {
public $variable = "mydefault";
public function change_variable($value) {
$this->variable = $value;
}
}
function display_juice() {
$class = new my_class;
echo $class->variable; // echo default value - 'mydefault'
$class->change_variable('newvalue');
echo $class->variable; // echo default value - 'newvalue'
}
display_juice();
Edit..
class my_class {
public $variable;
public function __construct() {
$this->variable = wp_get_current_user();
}
}

Answer 2

You need to make my_class_function() static, the you can call it with my_class::my_class_function()
http://php.net/manual/en/language.oop5.static.php
Also as suggested bellow, you need to return 'juice'.
return 'juice';

Answer 3

You currently don't return anything, you would have to do something like this:
class my_class() {
function my_class_function() {
$my_class_function_variable = 'juice';
return $my_class_function_variable;
}
}
function display_juice() {
$class_instance = new my_class(); //Needs to be inside the function
$my_class_function_variable = $class_instance->my_class_function();
echo $my_class_function_variable;
}
display_juice();
If you want to use a static function or variable you could do this, which eliminates the need for having to create an instance of my_class:
class my_class() {
static function my_class_function() {
return 'juice';
}
}
function display_juice() {
$my_class_function_variable = my_class::my_class_function();
echo $my_class_function_variable;
}
display_juice();

Answer 4

I would make the variable you're trying to access a public member
class my_class {
public $my_class_function_variable = 'juice';
public function my_class_function() {
}
}
$class_instance = new my_class();
function display_juice() {
echo my_class->$my_class_function_variable;
}
display_juice();