CascadiaPHP 2024

array_is_list

(PHP 8 >= 8.1.0)

array_is_list判断给定的 array 是否为 list

说明

array_is_list(array $array): bool

判断指定的 array 是否是 list。如果 array 的 key 由 0count($array)-1 的连续数字组成,则该数组就是 list。

参数

array

被检测的 array

返回值

如果 array 是 list 就返回 true,否则返回 false

示例

示例 #1 array_is_list() 示例

<?php

array_is_list
([]); // true
array_is_list(['apple', 2, 3]); // true
array_is_list([0 => 'apple', 'orange']); // true

// key 未从 0 开始
array_is_list([1 => 'apple', 'orange']); // false

// key 的顺序不正确
array_is_list([1 => 'apple', 0 => 'orange']); // false

// 包含非整数 key
array_is_list([0 => 'apple', 'foo' => 'bar']); // false

// 非连续 key
array_is_list([0 => 'apple', 2 => 'bar']); // false
?>

注释

注意:

空数组也会返回 true

参见

add a note

User Contributed Notes 5 notes

up
46
phpnet at jesseschalken dot com
2 years 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.

<?php

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;
}
}

?>
up
23
divinity76+spam at gmail dot com
2 years ago
slightly optimized version of phpnet at jesseschalken dot com's excellent array_is_list:

<?php

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)
up
15
Matteo Galletti
2 years ago
Polyfill implementation for PHP versions lower than 8.1.

<?php
if (!function_exists('array_is_list'))
{
function
array_is_list(array $a)
{
return
$a === [] || (array_keys($a) === range(0, count($a) - 1));
}
}
?>
up
1
maruerru
11 months ago
I think, this is the fastest polyfill:

<?php

if (!function_exists('array_is_list')) {
function
array_is_list(array $array)
{
return
$array === array_values($array);
}
}

?>
up
2
info at ensostudio dot ru
2 years ago
old school polyfill (:
<?php
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);
}
}
?>
To Top