Do these ternary operator output the same result?

Question

Is $time ?: 3600 equivalent to isset($time) ? $time : 3600 ?

Thank you all.

score 2 · Accepted Answer · answered May 20 '14 at 18:46

2

No. There are cases for which they evaluate to the same value, but they are not equivalent.

<?php
print $time ?: 3600;
print "\n";
print isset($time) ? $time : 3600;
print "\n\n";

$time = 0;
print $time ?: 3600;
print "\n";
print isset($time) ? $time : 3600;
print "\n\n";

$time = 30;
print $time ?: 3600;
print "\n";
print isset($time) ? $time : 3600;
print "\n\n";
?>

Output:

PHP Notice:  Undefined variable: time in /home/hq6/PHP/Test2.php on line 2
3600
3600

3600
0

30
30

answered May 20 '14 at 18:46

merlin2011

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I've tried with `print $time ?: 3600;`. And it output `3600`. ~~ – Lewis May 20 '14 at 18:56
@Orion, You have to test the cases both the cases where `$time` is defined, and the cases where `$time` is not defined. You also have to test the case where `$time = 0`. – merlin2011 May 20 '14 at 18:56
I tried with the `not defined` case. It's a little weird. – Lewis May 20 '14 at 19:01
@Orion, In order for two expressions to be *equivalent*, it must be the case that they output the same value for **all possible inputs**. – merlin2011 May 20 '14 at 19:03
I see that. I just want to get your first case. – Lewis May 20 '14 at 19:04
1

@Orion, The first case gives correct output but generates a warning. – merlin2011 May 20 '14 at 19:11

score 1 · Answer 2 · answered May 20 '14 at 18:44

1

No, not quite. $time ?: 3600 is similar to doing $time ? $time : 3600.

The difference would be if $time was 0. isset($time) would return TRUE so, you'd get $time (0), whereas if $time was 0 in the first one you'd get 3600.

answered May 20 '14 at 18:44

gen_Eric

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Do these ternary operator output the same result?

2 Answers2