Re: [boost] Re: [MPL] Making Tuples + minor doc-fix for MPL

From: David Abrahams (dave_at_[hidden])
Date: 2002-12-16 18:54:06

Terje Slettebø <tslettebo_at_[hidden]> writes:

>>From: "David A. Greene" <greened_at_[hidden]>
>>
>> Rozental, Gennadiy wrote:
>> >>Which example is that?  Is inherit_linearly documented somewhere?
>> >>
>> >
> http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/boost/boost/libs/mpl/example/
>> > inherit_linearly.cpp?rev=1.1&content-type=text/vnd.viewcvs-markup
>>
>> Well, that's not creating a boost::tuple.  :)  I could certainly use
>> mpl::fold or some similar algorithm to create boost::tuple<int,
>> boost::tuple<...> > > > but I'm not sure that "really" a boost::tuple
>> either.  cons<int, cons<...> > > > might be closer.

Yes, in fact, the cons< ... > structure satisfies all the requirements
for a tuple.  boost::tuple is just a friendly wrapper which presents
an easy interface.

> Here's one way. This handles tuples of up to three elements, but can easily
> be extended.
>
> It requires partial specialisation, but it could also be rewritten without
> it. In fact, I wrote a more complex version without it first, using
> compile-time if-else, but then realised I could use specialisations for
> this.

<snip>

Oof!

The version using fold<> is sure to be shorter and more-general!

-- 
                       David Abrahams
   dave_at_[hidden] * http://www.boost-consulting.com
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