在数组上进行迭代时，PHP中的foreach应该遵循的顺序是什么？

Question

I know that PHP array is not an array, it is actually an ordered hashmap, but it still does not make sense to me why if I run this code:

<?php

$teste = [];
$teste[2] = 'Test 2';
$teste[1] = 'Test 1';
$teste[3] = 'Test 3';

foreach ($teste as $t) {
    echo $t;
}

It prints the following:

Test 2
Test 1
Test 3

The result does not make sense to me, shouldn't it be ordered like:

Test 1
Test 2
Test 3

Answer 1

All arrays in PHP are actually ordered maps . Thus, the order in which key-value pairs are encountered in the map will depend primarily on the order in which they were added to the map. Arrays with a 0..n-1 index sequence in strict increasing order are simply a special case. You can test this by doing the following:

$my_arr = array();
$my_arr[3] = 'd';
$my_arr[1] = 'b';
$my_arr[2] = 'c';
$my_arr[0] = 'a';

// #1
echo json_encode($my_arr, JSON_PRETTY_PRINT) . "\n";

// #2
ksort($my_arr);
echo json_encode($my_arr, JSON_PRETTY_PRINT);

Output for #1:

{
    "3": "d",
    "1": "b",
    "2": "c",
    "0": "a"
}

Output for #2:

[
    "a",
    "b",
    "c",
    "d"
]

Note that the only difference between the two versions of $my_arr is the order of the keys. Out of order, the array is encoded as an object, but in order the array is encoded as a simple array.

Please review the linked section of the documentation for more information about PHP's arrays. This is already a well-documented feature of the language. If you desire a strict increasing sort order for your keys, use ksort() as shown in the example above.