Re: [boost] Re: The Wonder of Tuples

From: David A. Greene (greened_at_[hidden])
Date: 2002-12-18 14:34:36

Roland Richter wrote:
> David A. Greene wrote:
> 
>> The fundamental problem is that it's inconvenient to iterate through a
>> tuple.  All we have is the get<> template to access tuple elements.
>> Iterating is again conceptually simple -- just increment an index.
>> But the fact that get<> is a template implies the index must be a
>> compile-time constant, meaning we need a compile-time loop (or, if
>> you prefer, programmer-controlled loop unrolling) to iterate.
> 
>  Iteration through a tuple is indeed not so simple, but *recursion*
>  is, and you can do that at runtime.
> 
>  All you need is to get the head and the tail out of a tuple, and,
>  in turn construct a tuple out of head and tail. Boost.Tuple provides
>  that: "get_head()" and "get_tail()", although it is not mentioned
>  in the docs (why?).

That's an interesting solution and it will indeed do what I needed
to do.  The solution I presented is simply an unrolled version of
your solution.  It's kind of interesting to me that my solution is
in some way "MPL-like" in that there's an iterative algorithm
that's terminated with a sentinel (end-of-tuple index) while your
solution is more "Loki-like" in that it uses pattern-matching to
terminate a recursive algorithm.  Perhaps not a useful observation,
but an interesting one.  To me, anyway.

                              -Dave

-- 
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  and you know how big he was."  --  James P. Johnson