How to fix foreach warning: allocating an unneeded temporary container [-Wclazy-container-anti-pattern]

petr.bena

I am getting lot of these warning for this code:

        foreach (QString key, target->PropertyBag.keys()) // this is where I see it
        {
            if (!this->PropertyBag.contains(key))
                this->PropertyBag.insert(key, target->PropertyBag[key]);
            else
                this->PropertyBag[key] = target->PropertyBag[key];
        }

How should I change it so that I don't see the warning? Saving a list of keys in QList would probably dismiss the warning as well but it would also create a temporary container.

dheerendra

No point in calling same method again and again. Try the following.

QList keys = target->PropertyBag.keys();

foreach (QString key, keys){

}

petr.bena

is there a significant performance difference between the two?

petr.bena

also in my case PropertyBag is in most cases an empty hash, so I am thinking that maybe putting if (!PropertyBag.isEmpty()) in front would avoid unnecessary copy of empty qhash? This code is called in a loop for large amount of items, each item has its own PropertyBag.

kshegunov

for (auto & element : qAsConst(target->propertyBag))
    PropertyBag.insert(key, element.first);

foreach is deprecated.