Don't you access garbage then if the shadow is destroyed during qDeleteAll?

I would say it's undefined behavior. Either way, we should not call qDeleteAll on a container which is being "simultaneously" mutated.

it would be nice to have qSafeDeleteAll or something that takes a copy rather than a const ref.

It would be nice not to mutate a list that's being deleted

In D28074#628308, @broulik wrote:

It would be nice not to mutate a list that's being deleted

Well, we could do something like this (not sure whether it works though)

for (KWindowShadow *shadow : _shadows)
    disconnect(shadow, nullptr, this, nullptr);

qDeleteAll(_shadows);

or switch to QPointers

In D28074#628309, @zzag wrote:

Well, we could do something like this (not sure whether it works though)

for (KWindowShadow *shadow : _shadows)
    disconnect(shadow, nullptr, this, nullptr);

qDeleteAll(_shadows);

+1

Another way around is not to use qDeleteAll, e.g.

for( QWidget* widget : _widgets )
{ unregisterWidget( widget ); } // or uninstallShadows()

Either way, I'm open to suggestions. :-)

Alternatively, we could drop qDeleteAll( _widgets ); because the style is destroyed after all widgets have been deleted. So, it's sort of redundant.