PHP Exercises: Call a given function only once

Last update on May 30 2022 11:41:55 (UTC/GMT +8 hours)

PHP: Exercise-101 with Solution

Write a PHP program to call a given function only once.

Sample Solution: -

PHP Code:

<?php
//Licence: https://bit.ly/2CFA5XY

function once($function)
{
    return function (...$args) use ($function) {
        static $called = false;
        if ($called) {
            return;
        }
        $called = true;
        return $function(...$args);
    };
}

$add = function ($a, $b) {
    return $a + $b;
};

$once = once($add);

var_dump($once(10, 5));  
var_dump($once(20, 10));
  
?>

Sample Output:

int(15)
NULL

Flowchart:

PHP Code Editor:

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Previous:Write a PHP program to curry a function to take arguments in multiple calls.
Next: Write a PHP program to capture a variable number of arguments to a given function.

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PHP: Tips of the Day

How to Sort Multi-dimensional Array by Value?

Try a usort, If you are still on PHP 5.2 or earlier, you'll have to define a sorting function first:

Example:

function sortByOrder($a, $b) {
    return $a['order'] - $b['order'];
}

usort($myArray, 'sortByOrder');

Starting in PHP 5.3, you can use an anonymous function:

usort($myArray, function($a, $b) {
    return $a['order'] - $b['order'];
});

And finally with PHP 7 you can use the spaceship operator:

usort($myArray, function($a, $b) {
    return $a['order'] <=> $b['order'];
});

To extend this to multi-dimensional sorting, reference the second/third sorting elements if the first is zero - best explained below. You can also use this for sorting on sub-elements.

usort($myArray, function($a, $b) {
    $retval = $a['order'] <=> $b['order'];
    if ($retval == 0) {
        $retval = $a['suborder'] <=> $b['suborder'];
        if ($retval == 0) {
            $retval = $a['details']['subsuborder'] <=> $b['details']['subsuborder'];
        }
    }
    return $retval;
});

If you need to retain key associations, use uasort() - see comparison of array sorting functions in the manual

Ref : https://bit.ly/3i77vCC