Re: [boost] task_array<n> and variadic templates

Subject: Re: [boost] task_array<n> and variadic templates
From: Yechezkel Mett (ymett.on.boost_at_[hidden])
Date: 2008-11-19 10:32:51

On Wed, Nov 19, 2008 at 5:08 PM, Vicente Botet <vicente.botet_at_[hidden]> wrote:
>
> Comming back to my example, I need to store the tasks on an array. I do it now like this:
>
> template <>
> struct task_array<3> {
>    task arr_[3];
>    template <typename F_1, typename F_2, typename F_3>
>    task_array(F_1 f1, F_2 f2, F_3 f3) {
>        arr_[0]=task(f1);
>        arr_[1]=task(f2);
>        arr_[2]=task(f3);
>    }
> };
>
>
> I don't see a simple way to do it with variadic templates other than recursion.
>
> Is there a simple way to achieve this something like
>
> template <std::size N>
> struct task_array {
>   task arr_[N];
>   template <typename... F>
>    task_array(F... f) {
>        static_assert(sizeof...(T) == N, "Constructor must provide N parameters")
>    {
>        arr_={task(f)...};
>    }
> };

Recursion is the way to do anything with variadic templates :-)
But the following should work in theory:

template <std::size N>
struct task_array {
  task arr_[N];
  template <typename... F>
   task_array(F... f)
     : arr_({task(f)...})
   {
       static_assert(sizeof...(T) == N, "Constructor must provide N parameters")
   }
};

if you can find a compiler that supports the new initialisation syntax, that is.

Yechezkel Mett