如何将以'+'符号开头的数组的数字键转换为整数类型？

Question

According to the PHP Manual

The key can either be an integer or a string. The value can be of any type.

Additionally the following key casts will occur:

• Strings containing valid decimal integers, unless the number is preceded by a + sign, will be cast to the integer type. Eg the key "8" will actually be stored under 8. On the other hand "08" will not be cast, as it isn't a valid decimal integer.

As per about quotes I wrote following code. In below code the key +8 is getting cast to the integer type. How this is possible as the above rule says it should not happen?

<?php
$array = array(
    +8    => "a"
);
var_dump($array);
?>

Output :

array(1) {
  [8]=>
  string(1) "a"
}

Answer 1

Because +8 is an integer literal and, as such, the + sign is implicit and it makes no difference to add it or not:

var_dump(+8, 8);

 int(8) int(8) 

Nothing in the docs state that PHP will cast integers to strings. I think you just misread this sentence (emphasis mine):

Strings containing valid decimal integers, unless the number is preceded by a + sign

$array = array(
    7 => 'a',
    +8 => 'b',
    '+9' => 'c',
);
var_dump(array_keys($array));

 array(3) { [0]=> int(7) [1]=> int(8) [2]=> string(2) "+9" }