[heavenlyblue]

Technically copy-on-write is an implementation detail.

It may or may not be implemented this way.

[slavik81]

I mean that CoW classes like Qt's QStringList do the same data sharing without being immutable.

[slavik81]

Admittedly, it's pretty easy to accidentally make unnecessary non-const accesses in modern C++. An immutable API would certainly avoid a lot of qAsConst casts.