Toon Knapen wrote:

On Friday 26 April 2002 13:37, Aleksey Gurtovoy wrote:

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Toon Knapen wrote:

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I have a list of heterogeneous objects, e.g. [snip sample code]

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And now I want to have a function that can accumulate the value sof all the objects in the tuple, e.g. (pseudocode since my problem is exacly that I can't figure out how to code this)

template < typename TypleType > int accumulate_values(const TupleType& t) { int acc = 0; for(int i = 0 ; i < t.size() ; ++i ) acc += (get< i >( t )).value(); }

Can I do this using mpl (mpl looks great but I can't figure out how to do this).

It's not exactly a part of MPL (the library doesn't target "run-time" stuff to that extent yet; I hope it will some day), but "tuple extension" components I wrote some time ago

(http://groups.yahoo.com/group/boost/files/tuple_ext/tuple_ext-08-nov-01.zip )

allow one to do exactly these kinds of things: [snip aleksey's solution]

Thanks, I like tuple_ext a _lot_ !

I am glad you found it useful.

It would be great to have complete STL-like functionality like this.

Yep. The only problem with this is that we are going to end up with 3 STL-like libraries within the same language :) (the original one ("run-time"), the MPL one (pure compile time), and something in between, - HSTL (Heterogeneous Sequences Template Library :)). All three with the same algorithms, just written in different notation :). Emily's heterogeneous lists (www.oonumerics.org/tmpw01/winch.pdf, http://groups.yahoo.com/group/boost/files/alist-feb14-02.zip), 'tuple_ext' components, and MPL's v.2 half-run-time 'for_each' are obviously hanging around that "in between" thing.

Plans on adding this tuple_ext to the CVS ?

Some; I think it should be a full-fledged submission that would take the prior art and build a simple framework on it. It's not a large undertaking, though - most of the concepts and some code are already here :). Aleksey