Question

I’m trying to understand passing by reference. This is probably a bad analogy, but is it like Newton’s 3rd law (action-reaction pairs)?

For example, for the following code

$a = 4;
$b = 2;
$n = 42;
$a = &$b;

is

$a=$n the same as $b=$n? Isn’t the value of $a and $b stored in the same address?

Answer 1

If you assign these variables normally:

$a = 1;
$b = 2;
$c = 3;

Then the associations will look like this:

a --> 1
b --> 2
c --> 3

Now, if you make $c into a reference of $a, like this:

$a = 1;
$b = 2;
$c = &$a;

Then the associations will look like this:

a --> 1 <--.
b --> 2    |
c --------/

In other words, $a and $c point to the same value. Because they both point to the same value we can change either of the variables and they will both point to the new value.

$a = 5;
echo "$a $c"; // Output: "5 5"
$c = 10;
echo "$a $c"; // Output: "10 10"