Question

I wonder why this works strange. I understand that the difference is grouping, but does it matter in comparison?

$i = 0;
foreach ($items as $item) {
   echo ($i == 0) ? 'first_row' : ($i == sizeof($feedbacks)-2) ? 'last_row' : 'none';
   $i++;
}

returns

last_row
none
none
last_row

and

$i = 0;
foreach ($items as $item) {
   echo ($i == 0) ? 'first_row' : (($i == sizeof($feedbacks)-2) ? 'last_row' : 'none');
   $i++;
}

returns it correctly

first_row
none
none
last_row

Why is there a difference?

Answer 1

To use an explanation based on your code, a scaled down version would be:

for ($i=0; $i<5; $i++) {
   echo $i == 0 ? 'first_row' : $i == 4 ? 'last_row' : 'none';
}

In PHP, this is equivalent to writing:

for ($i=0; $i<5; $i++) {
   echo ($i == 0 ? 'first_row' : $i == 4) ? 'last_row' : 'none';
}

On the first go, $i has the value of 0, so the first ternary returns 'first_row' and that string is used as the conditional for the second ternary — which in boolean context evaluates to true — hence 'last_row' is returned.

If you regroup it:

for ($i=0; $i<5; $i++) {
   echo $i == 0 ? 'first_row' : ($i == 4 ? 'last_row' : 'none');
}

then the result of the first ternary will not interfere with the second ternary.