Array initialisation and key data types in PHP

#php

When initialising PHP array elements the order of the keys can result in changes to all the key types, even when you explicitly specify the key value/type.

$foo[0] = 'a';
$foo[1] = 'b';
$foo[2] = 'c';
$foo[3] = 'd';

// $foo has integer keys

$bar[0] = 'a';
$bar[1] = 'b';

// $bar has integer keys

$bar[3] = 'c';

// $bar now has string keys, because we skipped element 2
// this is despite us using an integer key

$bar[2] = 'd';

// $bar still has string keys, despite it having element 2
// and it being declared with an integer key

json_encode($foo) !== json_encode($bar);

// True