Interface should not have properties?

Question

My office colleague told me today that is bad practice to use properties in interfaces. He red that in some MSDN article(s), which I couldn't find (well I was trying few times on google, probably with wrong key words). He also told me that only methods should be in interface. Now, I am aware that is is not strict rule, since obviously in .net you can make property signature in interface and compile it.

But is this true to be a bad practice/design/oop? And why?

Pointing out to right literature or web resource would be helpful too.

Thanks

Answer 1

There is widely recognized term "code smell". I suggest introducing "programmer smell" concept - if someone insists on some rule, but can not explain why - it is a smell. Your colleague should be able to explain why properties in the interface are bad. If he can not - he is probably wrong even if article he is referring to is right.

That article may be was talking about some specific kinds of interfaces, may be it had something to do with COM and interoperability or whatever. Or he may be just got it wrong. Understanding rules and being able to explain them is important part of using rules.