How to achieve variadic virtual member function

Question

So I had this function...

virtual void CallRemoteFunction( const char* pServerGameObjectId, const char* pFunctionName, OVariant arg1 = OVariant(), OVariant arg2 = OVariant(), OVariant arg3 = OVariant(), OVariant arg4 = OVariant(), OVariant arg5 = OVariant(), OVariant arg6 = OVariant(), OVariant arg7 = OVariant(), OVariant arg8 = OVariant(), OVariant arg9 = OVariant() );

I decided to rewrite the function because, frankly, I was embarrassed by it. The function is straightforward... take a variable number of arguments of unknown type and do stuff.

I am fairly new to modern C++, so I did some searching and assumed I would find some simple/elegant new way of doing this. I imagined something like...

//hypothetical code
virtual void CallRemoteFunction( const char* pServerGameObjectId, const char* pFunctionName, ... args )
{
    std::vector<OVariant> argsArray;
    for (auto& arg : args )
    {
        argsArray.push_back(arg)
    }

    //do other stuff
 }
 //end hypothetical code

But in my searches, I could not find anything close. So could anybody kindly give me some ideas on how to refactor my original function into something cleaner or simpler? Note: the solution must be C++ 11 or older.

-Update- The function does not have to be virtual.
I want to be able to call the function like so...

CallRemoteFunction("serverID","someFunc",1,2,3);

Here is the implementation for reference

//calls function on client if this peer is a linked server or vice versa
void Peer::CallRemoteFunction( const char* pServerGameObjectId,  const char* 
pFunctionName, OVariant arg1, OVariant arg2, OVariant arg3, OVariant arg4, 
OVariant arg5, OVariant arg6, OVariant arg7, OVariant arg8, OVariant arg9 )
{
    Command command;
    command.SetObjectName( pServerGameObjectId );
    command.SetFunctionName( pFunctionName );
    command.ResetArgs();
    if ( arg1.IsValid() ){ command.PushArg( arg1 ); }
    if ( arg2.IsValid() ){ command.PushArg( arg2 ); }
    if ( arg3.IsValid() ){ command.PushArg( arg3 ); }
    if ( arg4.IsValid() ){ command.PushArg( arg4 ); }
    if ( arg5.IsValid() ){ command.PushArg( arg5 ); }
    if ( arg6.IsValid() ){ command.PushArg( arg6 ); }
    if ( arg7.IsValid() ){ command.PushArg( arg7 ); }
    if ( arg8.IsValid() ){ command.PushArg( arg8 ); }
    if ( arg9.IsValid() ){ command.PushArg( arg9 ); }

    LOG_DEBUG( "Calling Remote Function : " << pServerGameObjectId << "." << 
command.GetFunctionName() );
    ByteArray buffer( command.GetSerializeSize() );
    command.Serialize( buffer );

    ZMQMessage* request = new ZMQMessage();//deleted when sent via zmq
    request->addmem( buffer.GetBytes(), buffer.m_NumBytes );

    PushMessage( MDPW_REQUEST, m_pServiceId, request );
}

Answer 1

Sure, you can have that, if you want. You just have to combine a templated forwarder with a non-templated virtual function.

I'm using gsl::span ("What is a "span" and when should I use one?") and an automatic std::array (not a native one to avoid the special case of 0) for best generality, stability and efficiency.

virtual void DoCallRemoteFunction(
    const char* pServerGameObjectId,
    const char* pFunctionName,
    gsl::span<OVariant> args
) {
    ...
}

template<class... ARGS>
void CallRemoteFunction(
    const char* pServerGameObjectId,
    const char* pFunctionName,
    ARGS&&... args
) {
    std::array<OVariant, sizeof...(ARGS)> arr = { OVariant{std::forward<ARGS>(args)} ... };
    DoCallRemoteFunction(pServerGameObjectId, pFunctionName, arr);
}

I have given them different names because you presumably will override the virtual function, and probably don't want the API-function to be shadowed then.

Answer 2

If you're willing to accept slightly different call syntax (which e.g. std::max also uses), you can have a very elegant solution:

virtual void CallRemoteFunction( const char* pServerGameObjectId, const char* pFunctionName, std::initializer_list<QVariant> args )
{
    std::vector<OVariant> argsArray;
    for (auto& arg : args )
    {
        argsArray.push_back(arg)
    }

    //do other stuff
}

Called like this:

CallRemoteFunction("foo", "bar", { arg1, arg2, arg3 });