C++ difference between adding const-ness with static_cast and const_cast of “this” object?

Question

As per Scott Meyers, to prevent repetition of code in the const version of a getter and the non-const version of a getter, call the const version of the method from the non-cons

Answer 1

After re-reading Item 3 from Effective C++ 3rd Ed. I realize that he was actually advocating using both. Add const to call the const version, then cast away the const-ness of the return value (if there is one). In my particular case, there is no const return value, just a const-function so the wrapped-by-const_cast<> version is not needed and in effect causes there to be no difference between the two calls in question

(p. 13) Item 3: Use const whenever possible

...

(p. 23) Avoiding Duplication in const and Non- const Member Functions

...What you really want to do is implement operator[] functionality once and use it twice. That is, you want to have one version of operator[] call the other one. And that brings us to casting away constness.

...Casting away the const on the return value is safe, in this case, because whoever called the non-const operator[] must have had a non-const object in the first place....So having the non-const operator[] call the const version is a safe way to avoid code duplication, even though it requires a cast...

class TextBlock {
public:

...

    const char& operator[](std::size_t position) const      //same as before
    {
        ...
        ...
        ...
        return text[position];
    }

    char& operator[](std::size_t position)        //now just calls const op[]
    {
        //cast away const on op[]'s return type;
        //add const to *this's type;
        //call const version of op[].
        return const_cast(static_cast(*this)[position]);
    }
...
};

As you can see, the code has two casts, not one. We want the non-const operator[] ... To avoid infinite recursion, we have to specify that we want to call the const operator[], but there's no direct way to do that. Instead, we cast *this from its native type of TextBlock& to const TextBlock&. Yes, we use cast to add const! So we have two casts: one to add const to *this (so that our call to operator[] will call the const version), the second to remove the const from the *const operator[]'s return value.