What are the advantages and disadvantages of implementing classes in header files?

Question

I love the concept of DRY (don't repeat yourself [oops]), yet C++'s concept of header files goes against this rule of programming. Is there any drawback to defining a class member entirely in the header? If it's right to do for templates, why not for normal classes? I have some ideas for drawbacks and benefits, but what are yours?

Answer 1

Possible advantages of putting everything in header files:

• Less redundancy (which leads to easier changes, easier refactoring, etc.)
• May give compiler/linker better opportunities for optimization
• Often easier to incorporate into an existing project

Possible disadvantages of putting everything in header files:

• Longer compile/link cycles
• Loss of separation of interface and implementation
• Could lead to hard-to-resolve circular dependencies
• Lots of inlining could increase executable size
• Prevents binary compatibility of shared libraries/DLLs
• Upsets co-workers who prefer the traditional ways of using C++

Answer 2

Well - one problem is that typically implementations change much more often than class definitions - so for a large project you end up having to recompile the world for every small change.