Generator by reference - generator

Question

I am testing generator by reference of two ways:
N°1: It works
<?php
$value = 3;
function &gen_reference() {
global $value;
while ($value > 0) {
yield $value;
}
}
foreach (gen_reference() as &$number) {
--$number;
}
echo($value . PHP_EOL); // 0
N°2: It not display than I want.
<?php
class Test
{
public $data = [];
function __construct($data){
$this->data = $data;
}
function &getIterator() {
foreach ($this->data as $key => $value) {
yield $key => $value;
}
}
function printData()
{
foreach ($this->data as $key => $value) {
echo($key . ':' . $value . PHP_EOL);
}
}
}
$data = array('one'=>'Curly', 'two'=>'Larry', 'three'=>'Moe');
$t = new Test($data);
foreach ($t->getIterator() as $key => &$value) {
$value = strtoupper($value); // Does not update $this->data
}
$t->printData();
Display:
one:Curly
two:Larry
three:Moe
I expected:
one:CURLY
two:LARRY
three:MOE
Any correction or suggestion?

Answer 1

Add & to $value in &getIterator function for keep to reference:
function &getIterator() {
foreach ($this->data as $key => &$value) { // Here add & to $value
yield $key => $value;
}
}
Code complete:
class Test
{
public $data = [];
function __construct($data){
$this->data = $data;
}
function &getIterator() {
foreach ($this->data as $key => &$value) { // Here add & to $value
yield $key => $value;
}
}
function printData()
{
foreach ($this->data as $key => $value) {
echo($key . ':' . $value . PHP_EOL);
}
}
}
$data = array('one'=>'Curly', 'two'=>'Larry', 'three'=>'Moe');
$t = new Test($data);
foreach ($t->getIterator() as $key => &$value) {
$value = strtoupper($value); // Does not update $this->data
}
$t->printData();