[Interest] Q_FOREACH creating copy , was (no subject)

Gunnar Roth gunnar.roth at gmx.de
Mon Jun 29 19:16:55 CEST 2015

Hi Prav
> for (Container::const_iterator iter=container.cbegin(); iter!=container.cend(); ++iter) {
>  //...
> }
> But why this could be more insecure to container copy (as result of detaching) as Koehne Kai warns:
>    I'd be careful with such an advice, unless you understand the performance
>    implications (because range-based loop will sometimes detach the Qt
>    Container, which is potentially a lot more expensive than the shallow copy
>    foreach does)
> is still unclear for me.
> _
Maybe you can  read my mail from this morning. In short, i talked about
c++11 ranged base for loop which would look like

for( const auto & element : container) {
this can detach the container , as even as the element is const, the non const begin would be called if container is not a const instance.


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