Re: [boost] [Ann] Variadic Templates [Updated]

From: Douglas Gregor (doug.gregor_at_[hidden])
Date: 2006-08-06 20:35:14

On Aug 6, 2006, at 6:13 AM, Ion Gaztañaga wrote:
> Good. I can set the bar higher if you want ;-). What about storing the
> return value in a tuple:
>
> bool test()
> { /**/ }
>
> template<typename... Values>
> void test_all(const Values&... values) {
>     //Is this possible?
>     //tuple<decltype(test(Values))...> ret_tuple = ...
>
>     //or using "auto"
>     auto ret_tuple = variadic_unroll(test(values));
> }

No need for a "variadic_unroll"; just use make_tuple:

        auto ret_tuple = make_tuple(test(values)...)

> It would be also nice a way to define a tuple of N objects of the same
> type: auto tup = make_tuple_n<bool, 6>;

I bet you can write a short metaprogram to do this using variadic  
templates.

> And iterate at runtime in a tuple of N objects of the same type, to  
> get
> each value (the iterator would climb in the inheritance-emulation code
> when incremeting it):
>
> for( bool ok : ret_tuple )
>     std::cout << "return value:" << ok;

As Alisdair points out, we have array<>, which we can easily loop over.

And, of course, that std::cout << ... bit is just an expression, so  
you can "unroll" the loop like this:

   variadic_unroll(std::cout << "return value: " << ret_tuple...);

        Cheers,
        Doug