On 8/10/07, shunsuke <pstade.mb@gmail.com> wrote:
Giovanni Piero Deretta wrote:
Also note that Boost.Lambda can't be used here. A Boost.Lambda functor is not Assignable.
Yes, that is very unfortunate and I think it should be fixed.
I saw that oven uses a special wrapper to make boost.lambda objects copiable. What does it exactly do?
As you guess, the wrapper uses Boost.Optional. It's rather simple: http://tinyurl.com/2nvw59
The wrapper I use simply does a placement new in its assignment operator. This is very exception unsafe, but I presume that most (all?) lambda objects won't throw on copy constructor. Using boost.optional would give the basic exception safetly, but it does increase the size of the wrapper.
I'm not sure. Boost.Optional also seems to use placement-new.
Yes, but it also need a boolean to record the initialized/non initialized state. In this case, if you assume that copyconstruction of a lambda never throws (a strong assumption, but it works in my case), you can do without the bolean. My range expressions are growing larger and larger even without the extra bool :)
Anyway, Boost.Optional seems fundamental, because Boost.Lambda functors are not DefaultConstructible, which ForwardIterator requires.
Hum,. you are right. Probably I've just been lucky and never used an algo that needed to default construction of my iterators so far. I'll probably revert my code to use optional. gpd