PHP: something wrong with this closure syntax? [duplicate]

Question

I'm following along an old book and am on an exercise using function_exists

here's the code for the exercise

<?php
    function tagWrap($tag, $txt, $func = "") {
        if ((!empty($txt)) && (function_exists($func))) {
            $txt = $func($txt);
            return "<$tag>$txt</$tag>\n";
        }
    }

    function underline($txt) {
        return "<u>$txt</u>";
    }

    echo tagWrap('b', 'make me bold');
    echo tagWrap('i', 'underline me too', "underline");
    echo tagWrap('i', 'make me italic and quote me',
        create_function("$txt", "return \"&quot;$txt&quot;\";"));
?>

As expected, the first function call shows nothing because there's no function in the args, and the second shows correctly since the underline function is defined, issue is with the third call with the closure: it's supposed to show the text but it doesn't.

At first i thought to myself "that's silly, i'm ceating a function but am passing return as a string", but messing with it just left my IDE screaming at me so i guess PHP does work like that, so i've been messing around with '' "" and `` for a while now but there's no way for the third function call to show output.

Am i creating the closure wrong or is this a simple syntax issue when passing the strings?

create_function() is obsolete. It was deprecated in 7.2 and removed in 8.0. — Barmar
– Barmar, Commented May 22, 2024 at 20:39
The argument to function_exists() must be a function name, not a closure. — Barmar
– Barmar, Commented May 22, 2024 at 20:40
I think you're looking for is_callable(), not function_exists(). php.net/manual/en/function.is-callable.php — Barmar
– Barmar, Commented May 22, 2024 at 20:41
Get yourself a newer book. PHP has changed significantly in 20 years. — Barmar
– Barmar, Commented May 22, 2024 at 20:50
@Anacardo consider these working experiments with my rescripting of your code: 3v4l.org/NQjhg — mickmackusa
– mickmackusa ♦, Commented May 23, 2024 at 0:16

Barmar · Accepted Answer · 2024-05-22 20:49:32Z

3

The argument to function_exists() must be a string, which is looked up as a function name. You can't pass a closure to it. The correct test should be is_callable(), it will be true for a function name, an array [object, method_name], or a closure.

Since create_function() is obsolete, you should use an anonymous function or arrow function.

<?php
    function tagWrap($tag, $txt, $func = "") {
        if ((!empty($txt)) && (is_callable($func))) {
            $txt = $func($txt);
            return "<$tag>$txt</$tag>\n";
        }
    }

    function underline($txt) {
        return "<u>$txt</u>";
    }

    echo tagWrap('b', 'make me bold');
    echo tagWrap('i', 'underline me too', "underline");
    echo tagWrap('i', 'make me italic and quote me',
        fn($txt) => , "&quot;$txt&quot;");
?>

answered May 22, 2024 at 20:49

Barmar

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1 Comment

Anacardo Over a year ago

Yes sir, it works just fine adapting the closure to the new syntax and using is_callable() instead of function_exists() Thank you so much, i'll try to find a newer book to keep up with the times.

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