Why Does `in_array()` Return True for a Non-Existent Value in PHP?

In-array's Peculiar Behavior with TRUTH

PHP's in_array() function exhibits an unexpected behavior when working with an array containing the boolean TRUE.

Let's consider the following array:

$arr = [TRUE, "some string", "something else"];

Surprisingly, in_array("test", $arr) returns true, even though "test" is not in the array. The same unusual result arises with array_search("test", $arr), which returns 0.

This behavior is not a bug, but a well-documented feature.

Strictly Speaking: Understanding the Third Parameter

Both in_array() and array_search() possess an optional third parameter, $strict, which defaults to FALSE.

bool in_array ( mixed $needle , array $haystack [, bool $strict = FALSE ])

This means that, by default, both functions employ loose comparison (==). They evaluate values solely on equality, disregarding their types. Consequently, in the given example, TRUE == "any non-empty string" returns true because of type juggling.

Enforcing Rigor: Setting $strict to TRUE

To ensure accurate comparisons, you can set $strict to TRUE. Doing so forces PHP to use strict comparison (===), checking both the value and type of the values it compares.

$result = in_array("test", $arr, TRUE);
var_dump($result); // Output: bool(false)

In this case, in_array() correctly returns false, as expected.

Remember that understanding the nuances of type juggling and the role of $strict is crucial when using in_array() and array_search(). These functions offer powerful search capabilities, but their behavior can be unpredictable if these subtleties are overlooked.

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