Tobias Schwinger wrote:
Joel de Guzman wrote:
Eric Niebler wrote:
Christian Henning wrote:
Hi there, is it possible to have a stateful functor object when using fusion::for_each() loop.
I would like to to the following:
<snip code>
for_each takes the function object by reference to const, so you have to const qualify operator() and make the data members mutable so you can change them anyway. IMO, this is a bug in Fusion. There should be an overload of for_each
Tobias Schwinger wrote: that takes a function object by non-const reference.
For the function invokers I use by-value parameters and the templates are designed to allow explicitly specified template arguments to use references instead. The reason was that by-value arguments can be more efficient for small function objects (tracking side effects) and function pointers.
Really? Do you have some numbers to back that?
It might be worthwhile to consider this scheme as an alternative to overloading, especially for algorithms which call back multiple times.
Sure. Agreed; also, see below.
Stateful predicates should be supported, and Fusion should be explicit about where and when predicates are copied, so that the state doesn't get messed up.
I agree. This is one of the todo items. Noted and added in the queue.
No doubt here.
Ok, anyway, for the sake of discussion, the stl for_each is:
template