Modify Your Base Class Interface in Derived Classes-3 : Page 3

Name Injection
To fix this problem, you have to explicitly inject the name File::Open into the scope of NetworkFile::Open(). This way, any additional function called Open() that you declare in NetworkFile won't hide File::Open. To do so, use a using-declaration like this:

class NetworkFile : public DiskFile
{
public:
 using File::Open; //inject a name into current scope
 int Open(const wstring & path);
 //..
};

When you add a using-declaration of this kind, make sure that it appears in the public section of the class. Now you can use both overloaded versions of Open() in the derived class:

string path="\\usr\\image.bmp";
wstring wpath=L"\\usr\\image.bmp";

NetworkFile nf, nf2;
nf.Open(path); //OK, File::Open(const string &)
nf2.Open(wpath); //OK, NetworkFile::Open(const wstring &)

You may add as many overloaded versions of Open() as you like to NetworkFile:

class NetworkFile : public DiskFile
{
public:
 using File:Open; //inject name into current scope
 int Open(const wstring & path);
 int Open (const char * path);
 int Open (const wchar_t * path);
 //..
};

Likewise, any class that inherits from NetworkFile can use the same technique to add even more overloaded functions:

class UnixNetworkFile : public NetworkFile
{
public:
 using NetworkFile:Open; //inject all overloaded versions
 int Open(int descriptor);
//..
};

UnixNetworkFile nf1, nf2, nf3;
nf.Open(path);
nf.Open(wpath);
nf.Open(2); //opens stderr

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