During initialization php parses every value as expression. One can declare variables, do calculations, or even manipulate "current" array
<?php
$arr['A'] = [
&$arr, // circular reference
'key' => 'val',
$arr['B'] = [ // declare array, insert key and then value
'a' => 'b',
],
ucfirst(strtolower('SOME TEXT')),
true ? 'TRUE' : 'FALSE', // evaluate expression
$x = 3, // declare variable
$x *= 3, // perform calculations
];
var_dump($arr);
// Output
/*
array(2) {
'B' => array(1) {
'a' => string(1) "b"
}
'A' => array(7) {
[0] => array(2) {
'B' => array(1) {
...
}
'A' => &array
}
'key' => string(3) "val"
[1] => array(1) {
'a' => string(1) "b"
}
[2] => string(9) "Some text"
[3] => string(4) "TRUE"
[4] => int(3)
[5] => int(9)
}
}
*/
?>
