Comment by rezonant
5 years ago
Yes, its a great case for making the actual `children` collection private so that mutation must go through the interface methods instead. But still, iteration over the children is a likely use case, so you are left with either exposing the original object or returning a copy of the array (potentially slower, though this might not matter depending).
That problem could potentially be solved if the programming language supports returning some form of immutable reference/proxy/cursor that allows a caller to examine the container but without being able to change anything. Unfortunately, many popular languages don’t enforce transitive immutability in that situation, so even returning an “immutable” version of the container doesn’t prevent mutation of its contained values in those languages. Score a few more points for the languages with immutability-by-default or with robust ownership semantics and support for transitive immutability…
Very true. JS has object freezing but that would affect the class's own mutations. On the other hand you could make a single copy upon mutation, freeze it, and then return the frozen one for iteration if you wanted to. Kind of going a bit far though imho.