How to derive from a variadic template class in C++

Question

I have variadic template class which is just a wrapper for std::tuple :

template <typename ... Child>
class Tpl
{
public:
    Tpl() {}
    Tpl(Child ...args) : child(args...)
    {}

    template <typename T>
    T& Get()
    {
        return std::get<T>(child);
    }

    template <typename T>
    const T& GetConst()
    {
        return std::get<T>(child);
    }
private:
    std::tuple<Child ...> child;
};

How do I correctly derive a class from Tpl?

template <typename... Ts>
class SomeObject : public Tpl<Ts...>
{
public:
    SomeObject(/*Types ... args*/) /*: child(args...)*/
    {

    }
private:
    int num;        
};

The compiler (VS14 CTP 6) message just tells me:

syntax error: missing ',' before '<' in the line: class SomeObject: public Tpl<Ts...>

That looks correct to me, what compiler and version are you using? (I took the liberty of fixing `SomeObject`'s constructor name, judging from the error message that wasn't the cause of the error) — Praetorian, Mar 01 '15 at 00:45
`DbgGameObject` eh? So you're not posting the code you're testing. Test the MCVE then post the error message as it appears _for that MCVE_. — Lightness Races in Orbit, Mar 01 '15 at 00:54
There is CTP 6: http://www.visualstudio.com/news/vs2015-vs#ctp6 — Fabian, Mar 01 '15 at 12:51

score 1 · Accepted Answer · answered Mar 01 '15 at 00:53

1

The code is fine.

You didn't tell us what compiler (inc. its version) you're using, but presumably it has limited/no support for variadic templates or is buggy in this regard. Consider upgrading it or switching to something else entirely. GCC and Clang are both good.

answered Mar 01 '15 at 00:53

Lightness Races in Orbit

378,754
76
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1,055

I'm using the lastest version of Visual Studio 2015. I can't switch the compiler – Fabian Mar 01 '15 at 01:55
Then you cannot do what you want unless you find a workaround or wait until MS releases a new version with this bug fixed. – OmnipotentEntity Mar 01 '15 at 03:51
After a restart, a clean and rebuild it compiled with no erros. Sorry for wasting your time with that nonsens -_- – Fabian Mar 01 '15 at 12:51
@Fabian: Old code then. – Lightness Races in Orbit Mar 01 '15 at 15:35

How to derive from a variadic template class in C++

1 Answers1