In PHP, False is Sometimes True

This post is more than 18 months old. Since technology changes to rapidly, this content may be out of date (but that's not always the case). Please remember to verify any technical or programming information with the current release.

Sometimes it’s the little things that get you. This is more of just a reminder than anything else. One of the fun quirks (and I hesitate to call it a quirk because it’s technically working as defined) in PHP.

$flag = "false";
assert((bool) $flag === true);

The result here is true - why does this matter? Because of some sloppy programming, I had some code that was trying to use the value of some flag that was passed in from a JSON post request. Because I knew it was a string, I was casting it to a boolean. Of course this worked when the value was "true" but it wasn’t until a weird bug later that I noticed that it was casting "false" as true as well. It does this because it validate that the string is non-empty, not the content of the actual string. Doh!


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