php returning mixed data types - good or bad

Question

When returning values in php, is it considered good or bad practice to return mixed data types. I'm working on a project where I am constantly faced with methods that return an id number or null. I'm handling the null value by checking for null and returning -1 if it is null.

Another situation I find myself in a lot is where a method should do something and return a string. But sometimes it's not possible to return the string as it wasn't found or an exception happened. What's the best thing to do here? Return a string like 'failed' or something? This then creates a string coupling between methods, I think, as the calling method has to know exactly the string failure message to check for??

EDIT: OK there are a few different opinions already. I like the idea of returning false on failure and the actual result whatever its data type is on success. But... is there a defacto best practice when it comes to this? I mean, what do programmers in other languages do i.e. java and c++ etc in these situations?

Answer 1

What I usually do is if the method worked, return the value, and if it failed return FALSE. That's what a lot of PHP's built-in methods do. So, then you can just check if the function returned FALSE or not.

Answer 2

Returning mixed type is bad, at least today in 2013. Boom! The way to go is to split this:

BAD, mixed return type style:

function checkResult($data)
{
    if ($data) {
        ...
        return $stuff;
    } else {
        return false;
    } 
}

People will need additional logic to work checkRsult(), and they never know exactly what type will return.

GOOD, clearly fixed return type style:

Maybe the example is not really good, but it shows the way to go.

function doesResultExist($data)
{
    if ($data) {
        return true;
    }
    // default return
    return false;
}

function getResultData()
{
    ...
    return $stuff;   
}