Hướng dẫn array_is_list php

(PHP 8 >= 8.1.0)

array_is_list — Checks whether a given array is a list

Description

array_is_list(array $array): bool

Parameters

The array being evaluated.

Return Values

Returns true if array is a list, false otherwise.

Examples

Example #1 array_is_list() example

array_is_list

Notes

Note:

This function returns true on empty arrays.

phpnet at jesseschalken dot com ¶

8 months ago

Polyfills that call `array_keys()`, `array_values()` or `range()` are inefficient because they create new arrays unnecessarily.

Please use this polyfill instead which creates no new arrays and only does a single pass over the given array.

if (!function_exists("array_is_list")) {
    function array_is_list(array $array): bool
    {
        $i = 0;
        foreach ($array as $k => $v) {
            if ($k !== $i++) {
                return false;
            }
        }
        return true;
    }
}?>

divinity76+spam at gmail dot com ¶

4 months ago

slightly optimized version of phpnet at jesseschalken dot com's excellent array_is_list:

if (!function_exists("array_is_list")) {
    function array_is_list(array $array): bool
    {
        $i = -1;
        foreach ($array as $k => $v) {
            ++$i;
            if ($k !== $i) {
                return false;
            }
        }
        return true;
    }
}?>

benchmarks: https://3v4l.org/9BPqL

why is this faster you ask? because post-increment does more,

here is what pre-increment actually means:
step 1: increment the value by 1.
step 2: return the value.

here is what post-increment actually means:
step 1: create a copy of the original value.
step 2: increment the original value by 1.
step 3: return the copy.

another question might be "why didn't you write `if ($k !== ++$i) {` ?  ... that is a good question! turns out that ++$i;if($k!==$i){...} is faster on PHP7 than if($k !== ++$i){...} for reasons unknown to me.. (if you have an answer, feel free to email me about it!)

(i have NOT checked if PHP8/jit auto-optimize this stuff, but at least back in PHP7 it's true that pre-increment is faster than post-increment, and this polyfill is primarily for PHP7)

Matteo Galletti ¶

10 months ago

Polyfill implementation for PHP versions lower than 8.1.

if (!function_exists('array_is_list'))
{
    function array_is_list(array $a)
    {
        return $a === [] || (array_keys($a) === range(0, count($a) - 1));
    }
}
?>

info at ensostudio dot ru ¶

10 months ago

old school polyfill (:
if (!function_exists('array_is_list')) {
    function array_is_list(array $array)
    {
        if ($array === []) {
             return true;
        }
        $keys = array_keys($array);
        return $keys === array_keys($keys);
    }
}
?>

iradu at unix-world dot org ¶

7 months ago

// How about:

if(count(array_filter(array_keys($y_arr), 'is_string')) === 0) {
    echo 'non-associative ; is list';
} else {
    echo 'associative ; non list'
}