PHP strange behaviour with switch case and the string '-0'

Question

I've recently come across a very strange behaviour in the PHP switch case when dealing with the string '-0'.

/* 
The code below echos:
'How did that happen? "0" and "0" are two different strings.' 
*/

$myString = '-0';

switch($myString) {
    case '0':
       echo 'How did that happen? "-0" and "0" are two different strings.';
       break;
    case '-0':
       echo 'This is normal.';
       break;
}

Oddly, the switch statement above executes case '0'.

Going back to the code above, it seems that if you change the order of the cases and place case '-0' before case '0', it seems to work fine and execute case '-0' as it should.

Why is that? Is there reasoning behind this strange behaviour?

Answer 1

While writing this question, I found out that PHP does NOT use strict equality for validating switch cases (unlike other scripting languages such as JavaScript).

Therefore, case '0' executes if '0' == '-0', and since that is true, runs that instead (because it checked for that case first).

If case '-0' was placed first, it checks for that first, therefore executing that case, and since both cases are valid / TRUE, it runs the first case in the switch statement.