JuniorTheoryCommon

What does the program print?

PHP

<?php

$count = 0;
echo $count ?: 10, ' ', $count ?? 10, ' ', $limit ?? 5, "\n";

10 0 5

Expecting $count ?? 10 to give 10 because 0 looks empty: ?? falls back only on null or a variable that was never set, and 0 is a set value.
Expecting $count ?: 10 to keep 0: ?: falls back on any value that turns into false, and 0 does, so it gives 10.

JuniorTheoryCommon

PHP

<?php

$count = 0;
echo $count ?: 10, ' ', $count ?? 10, ' ', $limit ?? 5, "\n";

10 0 5

Expecting $count ?? 10 to give 10 because 0 looks empty: ?? falls back only on null or a variable that was never set, and 0 is a set value.
Expecting $count ?: 10 to keep 0: ?: falls back on any value that turns into false, and 0 does, so it gives 10.