Strange Fibonacci results using a list function - php

Question

I came across a very nice Fibonacci series implementation but I am having trouble understanding how exactly it works. Here are the two implementations I have tried in order to figure out the issue:
<?php
fibo(1000);
fibo2(1000);
function fibo($n){
list($a, $b) = [0, 1];
while($a<=$n){
echo $a . " ";
list($a, $b) = [$b, $a + $b];
}
echo "\n";
}
function fibo2($n){
$a = 0;
$b = 1;
while($a<=$n){
echo $a . " ";
$a = $b;
$b = $a + $b;
}
echo "\n";
}
?>
The above two functions produce the following results respectively:
fibo: 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
fibo2: 0 1 2 4 8 16 32 64 128 256 512
Could you please explain why the different results occur?

Answer 1

Explanation repeat:
It as to do with the fact that $a loses its value when it's set to $b's value in the 2nd implementation. In the 1st implementation, the use of list() makes those inputs parameters and thus their values aren't lost when it comes to the assignment. In this case for list(), the value of $a can correctly be used in the assignment when defining $b.
For example:
function fibo2($n){
$a = 0;
$b = 1;
while($a<=$n){
echo $a . " ";
$save_a = $a;
$a = $b;
$b = $save_a + $b;
}
echo "\n";
}
fibo2(1000);
This corrects the 2nd implementation.
With the output being:
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987