php returning mixed data types - good or bad

Question

When returnign values in php is it considered good or bad practivce to return mixed data types. Im working on a project where i am constantly being faced with methods that wither return and id number or null. Im handling the null value by checking for null and returning -1 if is null.

Another situation where i find myself in a lot is where a method should do something and return a string. But sometimes its not possible to return the string as it wasnt found or an exception happened. Whats best 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 be on success. But... is there a defacto best practice when it comes to this? I mean, what do programmers in otger 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

I think it is bad practice to return mixed data types. It is possible, as you pointed out, but think about the readability and maintainability of your code. Make sure you comment what you are returning and why, I think that is going to be most important. If you are expecting back an int and you return -1 instead of null, comment that, so you (or someone else) doesn't go crazy trying to figure out what you were trying to do.

Answer 3

Null is a fairly common return value to indicate that there is no return value. You should return null (not "failed", or -1) if the function wants to return no ID at all.

If it is exceptional that an ID was not found, you should throw an exception.

Answer 4

A function that returns mixed values is not considered bad., in fact thats the beauty of php, it being a dynamic language., so the thing to do is return false on failure and the required value if the function executes correctly,.

if( false == ( $data = do_something() ) ) return false;
else print_r( $data );

Answer 5

I agree with the answers above.

However if you design a whole system, the "best practice" would be to use exceptions: always return something meaningful, and in case of anomaly, throw an exception. The caller can then deal with the situations he knows how to face, and let somebody higher catch the rest.