On 21 June 2015 at 19:16, Julian Klappenbach wrote: > The issue occurred to me after I sent the email. > > begin() / end() return iterators by value, not reference. > > So, you're correct in identifying the value / reference issue. But to > be precise: you can't return an abstract class type *by value* from a > function.
I was already being precise when I said you can't return an abstract class type from a function. If you return by reference you are not returning a class type, you are returning a reference type :-) > If the return values of begin() / end() were returned and > accepted as a reference, then I believe this would work. This > difference is that return by value results in an implicit > instantiation, which would attempt to create the > abstract type. > > Given that the existing libs all are coded to return iterators by > value from begin() / end(), I would assume that converting the > range-for logic to work with references would cause some nasty > side-effects. That is not an option, the standard is very explicit about the behaviour of range-based for, and whatever begin() returns is copied by value, so still wouldn't work with abstract classes even if you changed your begin() to return a reference. See http://en.cppreference.com/w/cpp/language/range-for And this is still off-topic on this list.
