create a list for std::forward from ellipsis (...)

Question

I have a function like the following, which uses one object A to construct another object B, forwarding the B onto another method.

Code:

static bool ExecuteScriptFunction(CScriptHost* pHost, const std::wstring& strFunctionName, MList* plResult, const MList* plArgs)
{   
    auto MakeV8 = [&](const MList* pList) -> Local<Value>
    {
        Local<Value> var;
        CreateJSObjectFromCPPObject(pHost->GetIsolate(), pList, var);
        return var;
    }
    Local<Value> value = pHost->InvokeFunction(strFunctionName.c_str(), MakeV8(plArgs));

    // Snip //
}

I'd like to overload the function, so that I can pass it a variable amount of plArgs to pass to InvokeFunction - with the caveat that I need to do it via MakeV8.

To achieve this, std::forward seems like a likely tool for the job, as it means not relying on the less-modern va_* macros, and generally cleaner code, and also learning a bit about a part of the STL I haven't really needed to use before.

I think such an overload would look like the following, however, I am not sure of the behaviour of what I have written, or whether it achieves what I think it does, or whether it achieves anything at all!?

// call a javascript function in V8
template <class... Lists /* = MList*/>
static bool ExecuteScriptFunction(CScriptHost* pHost, const std::wstring& strFunctionName, MList* plResult, const Lists* ...args)
{   
    auto MakeV8 = [&](const MList* pList) -> Local<Value>
    {
        Local<Value> var;
        CreateJSObjectFromCPPObject(pHost->GetIsolate(), pList, var);
        return var;
    };

    // InvokeFunction handily already takes a variable list of Local<Value>s
    // I want to pass a ... of Local<Value>s that is generated from ...args     || || || || ||
    // So far, no squiggly red lines in VS 2015 on this line of code            \/ \/ \/ \/ \/
    Local<Value> value = pHost->InvokeFunction(strFunctionName.c_str(), std::forward<Local<Value>>(MakeV8(args))...);

    // Snip //
}

Does the following line of code achieve what I'm asking for? Local<Value> value = pHost->InvokeFunction(strFunctionName.c_str(), std::forward<Local<Value>>(MakeV8(args))...);

Or is there another incantation that will produce the behaviour I require?

Answer 1

Have you tried the following?

Local<Value> value = pHost->InvokeFunction(strFunctionName.c_str(), MakeV8(args)...);

The use of std::forward is of use only if your arguments are of type T&&, which is not the case with your pointers. Search for 'Perfect Forwarding' in case you need more details on that.

In order to expand the variadic argument pack, std::forward is not nequired, since the function argument list is already a context in which parameter packs are expanded.