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Make sure exactly one boolean of a given list is true?

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By User



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 .


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  1. Tips For AllJanuary 31, 2012 at 2:53 AM

    $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.

    ReplyDelete
  2. Tips For AllJanuary 31, 2012 at 2:53 AM

    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;

    ReplyDelete
  3. Tips For AllJanuary 31, 2012 at 2:53 AM

    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';
    }

    ReplyDelete
  4. Tips For AllJanuary 31, 2012 at 2:53 AM

    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.

    ReplyDelete
  5. Tips For AllJanuary 31, 2012 at 2:53 AM

    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.

    ReplyDelete

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