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  • Interface and Implementation in different files? If you need this by design this is still very common to define the interface (or abstract class) in languages such as Java/C# in one file and hide the implementation(s) in other files. This does not require old and tricky header files. Commented Dec 30, 2012 at 14:49
  • eh? isn't that what I said - you define the interface and the class implementation in 2 files. Commented Dec 31, 2012 at 0:30
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    well, that does not require header files and that does not make header files any better. Yes, they are needed in languages with a legacy, but as a concept they are not needed to split interface/implementation in different files (actually, they make it worse). Commented Jan 1, 2013 at 12:54
  • @Petter I think you misunderstand, conceptually they are no different - a header exists to provide an interface in the C language, and though you are right - you can combine the 2 (as many do with header-only C code) its not a best practice that I've seen followed in many places. All C# devs I've seen split the interface away from the class, for example. Its a good practice to do this as then you can include the interface file in multiple other files without pollution. Now, if you think that this split is a best practice (it is) then the way to achieve it in C is by using header files. Commented Mar 24, 2014 at 15:55
  • If headers were actually useful for separating interface and implementation, things like PImpl wouldn't be needed to hide private components and decouple end-users from having to recompile against them. Instead, we get the worst of both worlds. Headers feign a quickly dismissed facade of separation, while opening a myriad of pitfalls, which require verbose boilerplate code if you need to work around them. Commented Sep 20, 2015 at 22:16