Joel de Guzman <joel@boost-consulting.com> writes:
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.
And in fact it can be mutated, at least in most fusion structures. It's the _structure_ that can't be mutated. Just like boost::tuple. You can change the elements, but you can't change their number and type (in-place). -- Dave Abrahams Boost Consulting www.boost-consulting.com