Skip to main content

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

Image
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 .


Labels:

Comments

  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

Post a Comment

Popular posts from this blog

Why is this Javascript much *slower* than its jQuery equivalent?

By User
I have a HTML list of about 500 items and a "filter" box above it. I started by using jQuery to filter the list when I typed a letter (timing code added later): $('#filter').keyup( function() { var jqStart = (new Date).getTime(); var search = $(this).val().toLowerCase(); var $list = $('ul.ablist > li'); $list.each( function() { if ( $(this).text().toLowerCase().indexOf(search) === -1 ) $(this).hide(); else $(this).show(); } ); console.log('Time: ' + ((new Date).getTime() - jqStart)); } ); However, there was a couple of seconds delay after typing each letter (particularly the first letter). So I thought it may be slightly quicker if I used plain Javascript (I read recently that jQuery's each function is particularly slow). Here's my JS equivalent: document.getElementById('filter').addEventListener( 'keyup', function () { var jsStart = (new Date).getTime()...
3 comments
Read more

Is it possible to have IF statement in an Echo statement in PHP

By User
Thanks in advance. I did look at the other questions/answers that were similar and didn't find exactly what I was looking for. I'm trying to do this, am I on the right path? echo " <div id='tabs-".$match."'> <textarea id='".$match."' name='".$match."'>". if ($COLUMN_NAME === $match) { echo $FIELD_WITH_COLUMN_NAME; } else { } ."</textarea> <script type='text/javascript'> CKEDITOR.replace( '".$match."' ); </script> </div>"; I am getting the following error message in the browser: Parse error: syntax error, unexpected T_IF Please let me know if this is the right way to go about nesting an IF statement inside an echo. Thank you.
5 comments
Read more