Question 262188 in PHP Question posted in
Official manual can be found here.

How does PHP Match exactly evaluate condition?

I’m trying to use this code to print a text based on $num variable value, but when I assign a non-numeric value to it the output is much like I assigned a positive number, shouldn’t the output here be ‘Undefined Value’? I mean why isn’t executing the default case?

$num = ";";
match (true) {
    $num < 0 => print 'negative number',
    $num == 0 => print 'zero',
    $num > 0 => print 'positive number',
    default => 'Undefined Value',
};
//Output: positive number
Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    I did it like this and it worked:

        $num = ";";
    is_numeric($num) ? match (true) {
    $num < 0 => print 'negative number',
    $num == 0 => print 'zero',
    $num > 0 => print 'positive number',
    }
    : print "Undefined Value";
    //Output: Undefined Value

  2. 0

    A simpler test case:

    var_dump(';' > 0);

    bool(true)

    Demo

    If we check how comparison operators work, we understand that both operators are converted to numbers, but that isn’t true any more starting on PHP/8.0:

    var_dump(';' > 0, (int)';', (int)';' > 0, (float)';', (float)';' > 0);

    bool(true)
int(0)
bool(false)
float(0)
bool(false)

    Demo

    I suspect that documentation needs a fix and current rules are that right side operator is cast to string. As such, ; is 3B in ASCII and 0 is 30 (thus "smaller").

    Regarding your code, you could add a numeric check like this:

    match (true) {
    is_numeric($num) && $num < 0 => print 'negative number',
    is_numeric($num) && $num == 0 => print 'zero',
    is_numeric($num) && $num > 0 => print 'positive number',
    default => 'Undefined Value',
};

    But perhaps (and bear in mind that this is pretty much subjective) a match expression does not provide the leanest syntax for this use case and good old set of if/else can to the work just as fine. You can easily call is_numeric() once and avoid IEEE precision errors:

    if (!is_numeric($num)) {
    print 'Undefined Value';
} elseif ($num < 0) {
    print 'negative number';
} elseif ($num > 0) {
    print 'negative number';
} else {
    print 'zero';
}
    Login or Signup to reply.
Please signup or login to give your own answer.

Back To Top
Search