Pros and cons of using nested C++ classes and enum

Question

What are the pros and cons of using nested public C++ classes and enumerations? For example, suppose you have a class called printer, and this class also stores information on output trays, you could have:

class printer
{
public:
    std::string name_;

    enum TYPE
    {
        TYPE_LOCAL,
        TYPE_NETWORK,
    };

    class output_tray
    {
        ...
    };
    ...
};

printer prn;
printer::TYPE type;
printer::output_tray tray;

Alternatively:

class printer
{
public:
    std::string name_;
    ...
};

enum PRINTER_TYPE
{
    PRINTER_TYPE_LOCAL,
    PRINTER_TYPE_NETWORK,
};

class output_tray
{
    ...
};

printer prn;
PRINTER_TYPE type;
output_tray tray;

I can see the benefits of nesting private enums/classes, but when it comes to public ones, the office is split - it seems to be more of a style choice.

So, which do you prefer and why?

Answer 1

paercebal said everything I would say about nested enums.

WRT nested classes, my common and almost sole use case for them is when I have a class which is manipulating a specific type of resource, and I need a data class which represents something specific to that resource. In your case, output_tray might be a good example, but I don't generally use nested classes if the class is going to have any methods which are going to be called from outside the containing class, or is more than primarily a data class. I generally also don't nest data classes unless the contained class is not ever directly referenced outside the containing class.

So, for example, if I had a printer_manipulator class, it might have a contained class for printer manipulation errors, but printer itself would be a non-contained class.

Hope this helps. :)