Should you check for wrong parameter values in the constructor?

Question

Do you check for data validity in every constructor, or do you just assume the data is correct and throw exceptions in the specific function that has a problem with the parameter?

Answer 1

A constructor is a function too - why differentiate?

Creating an object implies that all the integrity checks have been done. It's perfectly reasonable to check parameters in a constructor and throw an exception once an illegal value has been detected.

Among all this simplifies debugging. When your program throws exception in a constructor you can observe a stack trace and often immediately see the cause. If you delay the check you'll then have to do more investigation to detect what earlier event causes the current error.

Answer 2

It's always better to have a fully-constructed object with all the invariants "satisfied" from the very beginning. Beware, however, of throwing exceptions from constructor in non-managed languages since that may result in a memory leak.