In an attempt to make std.range.Cycle const-correct, I had to do stuff like this:

    @property auto ref front()
    {
        return _original[_index % _original.length];
    }

    static if (is(typeof((cast(const R)_original)[0])) &&
               is(typeof((cast(const R)_original).length)))
    {
        @property auto const ref front() const
        {
            return _original[_index % _original.length];
        }
    }

In the associated review,Aandrei mentioned the possibility of adding const inferrence to the list of attributes that are inferred for templated member functions. And I think that this code highlights the need for something along those lines.

However, given the fact that there are many cases where you want both a non-const function which returns a non-const result and const function which returns a const result (as is the case in the example above), I think that inout inferrence would be a better choice (though if the return type doesn't have to be const on a const function and inout doesn't work with that, then inferring const would be fine then).