Re: C++0x: Tuple unpacking as arguments in function call

From:

ymett <ymett.on.usenet@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 12 Mar 2009 12:39:26 CST

Message-ID:

<ef276255-bcf6-40e5-b321-a7c8217e55e7@33g2000yqm.googlegroups.com>

On Mar 12, 11:46 am, metarox <legault.da...@gmail.com> wrote:

Hello,

I'd like to know what is the way to unpack a tuple into function call
arguments.

Try the following:

template<bool enable, class T> struct enable_if {};
template<class T> struct enable_if<true, T> { typedef T type; };

template<size_t argIndex, size_t argSize, class... Args, class...
Unpacked, class F>
inline typename enable_if<(argIndex == argSize),
void>::type apply_args_impl(const std::tuple<Args...>&& t, F f,
Unpacked&&... u)
{
     f(u...); // I think this should be f(std::forward<Unpacked>
(u)...);
}
template<size_t argIndex, size_t argSize, class... Args, class...
Unpacked, class F>
inline typename enable_if<(argIndex < argSize),
void>::type apply_args_impl(const std::tuple<Args...>&& t, F f,
Unpacked&&... u)
{
     apply_args_impl<argIndex + 1, argSize>(t, f, u...,
std::get<argIndex>(t));
}

template<class... Args, class F>
inline void apply_args(const std::tuple<Args...>&& t, F f)
{
     apply_args_impl<0, sizeof...(Args)>(t, f);
}

There are other possibilities, such as creating a list of indices.

Yechezkel Mett

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