Question

In my C++ header files I try to use forward declarations (class MyClass;) instead of #including the class header, as recommended in many C++ coding standards (the Google C++ Style Guide is one).

Unfortunately, when I introduce enumerations, I can’t do the forward declaration any more. Like this:

//// myclass1.hpp ////  class MyClass1 {     enum MyEnum1     {         Enum_A, Enum_B, Enum_C     }; };  //// myclass2.hpp ////  // I want to avoid this #include 'myclass1.hpp'  // I'd prefer to do this (forward declaration) class MyClass1;  class MyClass2 {     // This is o.k.: I only need to forward declare MyClass1     MyClass1* ptr;      // This forces me to #include, but I don't want to!     void func( MyClass1::MyEnum1 e ); }; 

The best solution I can think of so far is to replace enums with member constants:

//// myclass1.hpp  ////  MyClass1 {     static const int Enum_A;     static const int Enum_B;     static const int Enum_C; };  //// myclass1.cpp ////  const int Enum_A = 1; const int Enum_B = 2; const int Enum_C = 3; 

In this case, though, the solution seems worse than the problem.

I’m currently looking through Large Scale C++ Software Design (Lakos) and Working Effectively with Legacy Code (Feathers) for dependency breaking techniques, but I haven’t found a good solution yet.

Answer 1

You cannot forward declare enum values – and your workaround is a step down the path to complete madness.

Are you experiencing any major compilation slowdowns caused by #including headers? If not, just #include them. Use of forward declarations is not ‘best practice’ it is a hack.