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phpoperator-precedence

type casting and equal operator precedence in php

Why do these 2 statements not output the same result?
The only reason I can imagine is operator precedence which appears to the same for == and ===.

$a = (bool) 4 == 4;
$b = (bool) 4 === 4;

var_dump($a); // bool(true)
var_dump($b); // bool(false)
Solution

  • Yes, operator precedence is the same for == and ===. Clearly the difference here is the operator itself.

    First we have to acknowledge that type casting has a higher precedence than these two comparison operators. So, in reality, you're doing:

    $a = (TRUE == 4);
$b = (TRUE === 4);

    When you do a == you're simply trying to see if the values are equal. Only values of the same type can be compared. Since you start with a boolean, the number 4 will therefore also be turned into a boolean. This is called type juggling. We already know that (bool)4 is TRUE. So $a must be TRUE.

    However, when you do a === there is no type juggling, instead it will only return TRUE if the two operands have the same value and type. Since a boolean isn't the same type as an integer $b must be FALSE.