Scoped using-directive within a struct/class declaration? [duplicate]

Answer 1

The obvious benefit of namespaces is that they allow you to avoid naming conflicts. However, by introducing an entire namespace into a class declaration, this benefit is voided. It's entirely possible that a function in the System namespace could conflict with your own Bar::MemberFunc function. You even note this in your sample code when you added the comment "no conflict with this".

You obviously don't want to introduce entire namespaces into your class like this:

using namespace System;
using namespace System::Network;
using namespace System::Network::Win32::Sockets;

And you can't add more narrowly scoped using statements like this into a class declaration. Putting these directly into a class declaration is illegal.

using System::Network::Win32::Sockets::Handle;
using System::Network::Win32::Sockets::Error;

---

What you can do is use the unnamed namespace. So, your header file would look something like this:

namespace {
    using System::Network::Win32::Sockets::Handle;
    using System::Network::Win32::Sockets::Error;
}

class Foo : public Bar
{
    using Bar::MemberFunc;

    // clean!
    void FooBar(Handle handle, Error& error /*, more declarations*/);
};

---

This has three distinct advantages.

1. The contents of entire namespaces are not introduced. This helps to more easily avoid naming conflicts.
2. You have a list, before your class declaration, of what your class depends upon to work correctly.
3. Your function declarations are clean.

Please correct me if I'm wrong; I only briefly tested this. Quickly wrote up an example, and it compiled.