Make sure exactly one boolean of a given list is true?
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20-04-2021 - |
Question
If I have the following booleans
const YESTERDAY = false;
const TODAY = true;
const TOMORROW = false;
What code can I write to make sure exactly one is true?
I've tried this:
$x = self::YESTERDAY ^ self::TODAY ^ self::TOMORROW;
The problem is that with all three constants set to true
then $x
is true
.
Solution
$x = ((int) self::YESTERDAY) + ((int) self::TODAY) + ((int) self::TOMORROW);
Then if $x === 1;
You've got what you need.
EDITED:
Even without type casts (int)
, it works well, thanks to @DaveRandom, so:
if (self::YESTERDAY + self::TODAY + self::TOMORROW == 1) {}
, as for me.
OTHER TIPS
The neatest way I can think of is array_sum()
:
if (array_sum(array(self::YESTERDAY, self::TODAY, self::TOMORROW)) == 1) {
// Do something
}
EDIT Actually, all you need to do it replace the ^
with +
in your original attempt, and it achieves the same thing:
$x = self::YESTERDAY + self::TODAY + self::TOMORROW;
This turns $x
into the number of TRUE
values. So for a boolean output use:
$ok = self::YESTERDAY + self::TODAY + self::TOMORROW === 1;
Just as an alternative to devdRew's answer
$x = array_count_values(array((int) self::YESTERDAY,(int) self::TODAY,(int) self::TOMORROW));
if (isset($x[1]) && $x[1] == 1) {
echo 'Only one TRUE';
}
You can loop over a list of your variables and break when you found a second boolean that is true:
$moreThanOneTrue=false;
$oneTrue;
foreach ($BOOL_VAR_ARRAY as $bool) {
if ($bool) {
if($oneTrue) {
$moreThanOneTrue=true;
break;
}
$oneTrue=true;
}
}
Like this it's more handy when you have more than three variables.
x will return true if and only if one is true and others are false.
$x = ($a && !($b || $c)) || ($b && !($a || $c)) || ($c && !($a || $b));
May be a bad code, but works.
a ^ b ^ c ^ (a & b & c)
is the expresion you look for.