[boost] Re: tuple patch (constructing from a pair)

From: Joel de Guzman (joel_at_[hidden])
Date: 2005-02-15 09:52:52

Larry Evans wrote:
> On 02/15/2005 08:08 AM, Larry Evans wrote:
> [snip]
> 
>>> Yes, it is a non-member function. No, it does not mutate s.
>>> It does return another set. It is purely functional (no side-
>>> effects).
> 
> Then it's different from tuple<T1,...,Tn> since any mutating
> operation Ti::op on an instance of Ti can be performed on the
> corresponding member variable in an instance of tuple<T1,...,Tn>?

I don't understand what you are saying.

> See boost-sandbox.sourceforge.net/vault/cppljevans/field_visitor_tests
> /field_sets.hpp for an example of what I had thought you were
> talking about here:
> 
>  > fusion::vector, fusion::list, fusion::set and fusion::map
>  > all have data. These are different incarnations of the
>  > tuple with different characteristics.
> 
> when you said fusion::set had data.  Having data implies, at least
> to me, that the data can be modified.

I do not understand why we are having an impedance mismatch here.
It seems to me that we're in different universes. I do not even
understand why this matters at all. Having data *does not* imply
that the data is mutable. It can be const, for example. Or, in
purely functional terms, you do not wish to have side-effects.
Still, the data is there, in real bits and bytes.

Cheers,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net