Re: Fusion first contact & tuples everywhere was Re: [boost] mpl , tuples

From: Mat Marcus (mat-boost_at_[hidden])
Date: 2003-11-17 13:18:01

--On Monday, November 17, 2003 1:50 PM +0100 Bernard 
<yahoo_at_[hidden]> wrote:
[snip]

> It seems only logical to me when doing metaprogramming:
> You want to work with fonctions, so you have to know things about
> them  (eg. number and types of arguments). Why would you not decide
> that  every fonction should only take one argument ? Of course it
> would be  a tuple. All the ugly code handling differents number of
> arguments  (and limit on that number) would be factored in tuple.
> Other meta  programming libs would know that they only have to
> handle one args,  and they can then query about the number of
> elements in the tuple  etc....
> Such a convention must be used across the board to be useful and
> this  is not possible for classical dynamic C++, but if you are to
> decide  convention for compile time C++, I do not see any reason not
> to do  it.
> I would also define integral arguments to be wrapped in int_<>
> (uint_<> ) for consistency.
>
> I know it my sound strange, but I really think that such a
> "restricted" API would only be beneficial, because it would only
> give  more powerful meta-programming.

[snip]

Yes, there are a number of folks who have been working on making this 
possible for some time. IMO, one aim of N1484, the type-safe variadic 
proposal is to bring this goal closer to reality for regular C++ 
functions (and possibly also structs). We would like to be able to 
write functions (and meta-functions for that matter) that accept a 
single tuple/"parameter pack" (or struct) and programmatically walk 
through the args/members (and/or their types). Furthermore it would be 
desirable to be able to directly "uncurry" one of these tuples/"packs" 
so as to be able to directly and apply foo() from some overload set 
even if foo() is written using traditional 
multiple-comma-separated-argument style. There is also a desire for 
better syntax/support for tuple-like creatures in C++ '0x. Some of us 
spent a bit of time discussing this in Kona and there *may* be an 
enhanced version of 
<http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1483.pdf> 
reflecting these ideas for the Sydney meeting.

 - Mat