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@ 2024-01-20T03:11:15Z

<?php

function isPalindrome(string &$str): bool
{
    if (strlen($str) <= 1) {
        return true; // reached the middle of the palindrome successfully
    }
    if ($str[0] !== $str[strlen($str) - 1]) {
        return false; // outermost characters are not identical, halt processing
    }
    $str = substr($str, 1, -1);
    return (__FUNCTION__)($str); // traverse deeper and bubble outcome to top level
}

function sanitizePalindrome(&$str)
{
    return preg_replace('/[^a-z]+/', '', strtolower($str));    
}

$tests = [
    'radar',
    'f',
    'neveroddoreven',
    'foo',
    'palindrome',
    'Red rum, sir, is murder'
];
foreach ($tests as $test) {
    $test = sanitizePalindrome($test); // this is optional
    printf("%20s : %s\n", $test, json_encode(isPalindrome($test)));
}

Output for git.master, git.master_jit, rfc.property-hooks: radar : true f : true neveroddoreven : true foo : false palindrome : false redrumsirismurder : true

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2020-03-21 RFC: Is_Literal - declined
2020-12-04 Enumerations - included in PHP 8.1
2018-06-15 Typed Properties v2 - implemented in PHP 7.4
2016-08-12 Object typehint - included in PHP 7.2
2016-08-14 Arrow functions - withdrawn
2016-05-29 array_change_keys() - withdrawn
2016-04-19 Lexical scope support for anonymous classes - suspended
2016-04-17 Functional Interfaces - declined
2016-03-16 Typed Properties - superseded in favor of Typed Properties 2.0
2015-08-27 Callable Prototypes - declined
2015-05-01 Short Closures - declined / withdrawn in favor of Arrow Functions
2015-02-18 Scalar type hints v5 - included in PHP 7
2015-02-14 Union Types - declined
2013-09-22 Anonymous classes - included in PHP 7

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