Internal typedefs in C++ - good style or bad style?

Question

Something I have found myself doing often lately is declaring typedefs relevant to a particular class inside that class, i.e.

class Lorem
{
    typedef boost         


        

Answer 1

Currently I'm working on code, that intensively uses these kind of typedefs. So far that is fine.

But I noticed that there are quite often iterative typedefs, the definitions are split among several classes, and you never really know what type you are dealing with. My task is to summarize the size of some complex data structures hidden behind these typedefs - so I can't rely on existing interfaces. In combination with three to six levels of nested namespaces and then it becomes confusing.

So before using them, there are some points to be considered

• Does anyone else need these typedefs? Is the class used a lot by other classes?
• Do I shorten the usage or hide the class? (In case of hiding you also could think of interfaces.)
• Are other people working with the code? How do they do it? Will they think it is easier or will they become confused?

Answer 2

I think it is excellent style, and I use it myself. It is always best to limit the scope of names as much as possible, and use of classes is the best way to do this in C++. For example, the C++ Standard library makes heavy use of typedefs within classes.

Answer 3

I recommend to move those typedefs outside the class. This way, you remove direct dependency on shared pointer and vector classes and you can include them only when needed. Unless you are using those types in your class implementation, I consider they shouldn't be inner typedefs.

The reasons you like it are still matched, since they are solved by the type aliasing through typedef, not by declaring them inside your class.