How Can We Gracefully Handle Duplicate Const and Non-Const Getter Methods?

Graceful Handling of Duplicate, Const, and Non-Const Getters

As programmers, we often encounter the issue of having both const and non-const versions of getter methods in our classes. While implementing them separately can lead to code duplication, finding an elegant solution to this conundrum can be challenging.

The Challenge

In the example provided, the class Foobar requires two getSomething() methods: one non-const (Something& getSomething(int index)) and one const (const Something& getSomething(int index) const). However, trying to implement these methods with the other inevitably results in compiler errors. Casting the non-const version from the const version is also a necessary evil.

The Elegant Solution

Although an absolutely pristine solution might not be feasible, the most commonly recommended approach is casting away the const from the other function. While not exactly aesthetically pleasing, it's a safe technique since the calling member function is non-const, which means the object itself is non-const and casting away the const is permissible.

Consider the following code snippet as an example:

class Foo
{
public:
    const int& get() const
    {
        // non-trivial work
        return foo;
    }

    int& get()
    {
        return const_cast<int&>(const_cast<const Foo*>(this)->get());
    }
};

In this example, the non-const version of get() casts away the const from the const version, allowing it to modify the object itself.

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