How do I remove code duplication between similar const and non-const member functions?

Question

Let\'s say I have the following class X where I want to return access to an internal member:

class Z
{
    // details
};

class X
{
    std::vec         


        

Answer 1

I'd suggest a private helper static function template, like this:

class X
{
    std::vector vecZ;

    // ReturnType is explicitly 'Z&' or 'const Z&'
    // ThisType is deduced to be 'X' or 'const X'
    template 
    static ReturnType Z_impl(ThisType& self, size_t index)
    {
        // massive amounts of code for validating index
        ReturnType ret = self.vecZ[index];
        // even more code for determining, blah, blah...
        return ret;
    }

public:
    Z& Z(size_t index)
    {
        return Z_impl(*this, index);
    }
    const Z& Z(size_t index) const
    {
        return Z_impl(*this, index);
    }
};