Question: I would like to ask question regarding internal helper class in C++. What is the best way to structure this? 

Let me clarify what do I mean by internal helper class by example.

```
// MyClass.h
class MyClass
{
    int myData;
    bool isSomething;
    ...
public:
    void DoSomething();
};

// MyClass.cpp
// This is what I mean by internal helper function. Helper function that's only visible int the implementation file (.cpp) but requires access to the private members of the class.
static void DoSomethingInternal( MyClass *myClass )
{
   // Access myClass private members
}

void MyClass::DoSomething()
{
    ...
    DoSomethingInternal(this);
    ...
}

```

I know that declaring friend function can be a solution. However, it makes the class declaration ugly. In addition, for every new helper function, I have to add a friend function.

Is there an idiom/design pattern for this? I have been searching in the Internet, but didn't find any.

Thank you in advance. Your answers are greatly appreciated.

Answer: 
There are couple of ways to accomplish that.

1. Use a helper class/function in the .cpp file if the helper functions don't need access to the data directly. I would recommend this method ahead of the next method.

In the .cpp file:

```
// Create a namespace that is unique to the file
namespace MyClassNS
{
   namespace HelperAPI
   {
      void DoSomethingInternal(MyClass* obj) { ... }
   }
}

using namespace MyClassNS;
void MyClass::DoSomething()
{
    ...
    // 
    HelperAPI::DoSomethingInternal(this);
    ...
}

```
2. Use the [pimple idiom](https://en.wikipedia.org/wiki/Opaque_pointer). When using this idiom, you can add any number of helper functions in the private data class without touching the public interface of the class.
As per the upvoted answer given by StenSoft, you should implement the methods inside the class. However, if that is not an option for some reason, then use helpers. If even that is not an option, then use reflection. If even that is not an option, then use a command listener inside your class. If even that is not an option, then watch a tutorial.