Using C++11 range-based for loop correctly in Qt

Question

According to this talk there is a certain pitfall when using C++11 range base for on Qt containers. Consider:

QList list;

for(c         


        

Answer 1

template
std::remove_reference_t const& as_const(T&&t){return t;}

might help. An implicitly shared object returned an rvalue can implicitly detect write-shraring (and detatch) due to non-const iteration.

This gives you:

for(auto&&item : as_const(foo()))
{
}

which lets you iterate in a const way (and pretty clearly).

If you need reference lifetime extension to work, have 2 overloads:

template
T const as_const(T&&t){return std::forward(t);}
template
T const& as_const(T&t){return t;}

But iterating over const rvalues and caring about it is often a design error: they are throw away copies, why does it matter if you edit them? And if you behave very differently based off const qualification, that will bite you elsewhere.