Questions tagged [type-coercion]

Type coercion occurs in weakly typed languages (like javascript or php). Consider this PHP code

$x = '1'; // string
$y = $x + 1;
echo $y;

$x is a string, but we call it like an integer when setting $y. So the PHP engine coerces '1' (which is a string data type) into an integer for the purposes of math. As such, the script echoes 2 because the string 1 can be coerced neatly into integer 1. But not everything is so neatly handled

$x = 'a';
$y = $x + 1;
var_dump($y);

Now, 'a' is not readily coerced into a number. As such, we get back integer(1) because PHP coerces strings to 0 (modern PHP emits a E_WARNING that this is happening).

This most often rears itself in doing comparisons. Consider this code

$x = 'Something';
echo (strpos($x, 'Some') != false) ? 'Found it!' : 'Did not find it';

This script doesn't run like we expect. It tells us it didn't find it when we know it should have found it. The problem is that strpos can return a boolean false or the position of where it found the match. In this case, the match was at position 0. Our test then becomes

if( 0 == false )

Type coercion nails us here because 0 is coerced into false in PHP. PHP and Javascript both have a workaround for this, however. We can use === and !== to tell the interpreter to not coerce before comparing. If we tell PHP not to coerce the 0, we get back the results we expect

echo (strpos($x, 'Some') !== false) ? 'Found it!' : 'Did not find it';