Immutable C++ container class

Question

Say that I have a C++ class, Container, that contains some elements of type Element. For various reasons, it is inefficient, undesirable, unnecessary,

Answer 1

As long as your object can provider a conforming const_iterator it doesn't have to have anything else. It should be pretty easy to implement this on your container class.

(If applicable, look at the Boost.Iterators library; it has iterator_facade and iterator_adaptor classes to help you with the nitty-gritty details)

Answer 2

The STL doesn't define any lesser concepts; mostly because the idea of const is usually expressed on a per-iterator or per-reference level, not on a per-class level.

You shouldn't provide iterator with unexpected semantics, only provide const_iterator. This allows client code to fail in the most logical place (with the most readable error message) if they make a mistake.

Possibly the easiest way to do it would be to encapsulate it and prevent all non-const aliases.

class example {
    std::list<sometype> stuff;
public:
    void Process(...) { ... }
    const std::list<sometype>& Results() { return stuff; }
};

Now any client code knows exactly what they can do with the return value of Results- nada that requires mutation.