Using nested classes to modularize large application code?

Question

I'm building a large Desktop application, which will have a range of functionality, for each I wish to have a specific class.

I'm thinking of using a nested class structure to modularize the code and ensure separation of interface vs implementation:

class Manager
{
  public:
    Manager(); //Initialise *t and *wapi in constructor
    ~Manager(); //Delete *t and *wapi in destructor
  private:
    class Transport;
    Transport *t;
    class WinAPI;
    WinAPI *wapi;
};

class Manager::Transport
{
  public:
    Transport(); //Initialise *tcp and *http in constructor
    ~Transport(); //Delete *tcp and *http in destructor
  private:
    class TCPSocket;
    TCPSocket *tcp;
    class HTTP;
    HTTP *http;
};

class Manager::Transport::TCPSocket {};
class Manager::Transport::HTTP {};

class Manager::WinAPI 
{ 
  ... 
};

This is the first time I've built a large embedded application - are there any issues/other considerations I should consider before taking this approach?

Answer 1

Immediate questions are:

1. Are TCP sockets and HTTP connections really specific to your Manager::Transport nested class?
2. How will you unit test them if they're not accessible outside Manager?
3. Will anything other than a Manager ever need a Transport?

to which at a guess I'd probably answer No, With unnecessary difficulty, and Maybe, respectively.

You don't need this nesting to modularize the code - if anything it seems to have encouraged moving unrelated declarations into the same place.

Socket wrapper, and logical connection objects, look like part of a platform abstraction layer. This would normally go below your business object layer, not inside it.