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

From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2006-08-06 06:13:30

>> It would nice (just an idea) to have a way to execute an expression  
>> for
>> every parameter, just like it was a function unrolling, implemented  
>> with
>> with macros:
>>
>>     template<typename... Values>
>>     void push back all(const T& value, const Values&... values) {
>>        std::variadic_unroll(push_back(value));
>>     }
>>
>> Just an idea for the future. I don't know if implementing this is too
>> difficult. That would help with compilation time.
> 
> Oh, you can do that already, if you don't mind turning that push_back  
> call into a non-void expression:
> 
>    template<typename... Args>
>    void variadic_unroll(const Args&...) { }
> 
>    template<typename... Values>
>    void push_back_all(const Values&... values) {
>      variadic_unroll((push_back(values), 0)...);
>    }

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));
}

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>;

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;

Keep up the good work!

Ion