Compile-time 'String' Manipulation with Variadic Templates

Question

Hey all, I\'m currently trying to write a compile-time string encryption (using the words \'string\' and \'encryption\' quite loosely) lib.

What I have so far is as

Answer 1

If you just want to operate on one character at a time its easy:

template struct add_three {
    enum { value = c+3 };
};

template  struct EncryptCharsA {
    static const char value[sizeof...(Chars) + 1];
};

template
char const EncryptCharsA::value[sizeof...(Chars) + 1] = {
    add_three::value...
};

int main() {   
    std::cout << EncryptCharsA<'A','B','C'>::value << std::endl;
    // prints "DEF"
}

Note that CountArgs is redundant (that's what sizeof... is for) and that this uses element-wise transformation of the elements in a parameter-pack.

---

To make the transformation dependent on previous results, one option would be to consume the characters recursively, one at a time, and incrementally build a new template from that:

template struct StringBuilder {
    template struct add_char {
        typedef StringBuilder type;
    };

    static const char value[sizeof...(P)+1];
};

template const char StringBuilder::value[sizeof...(P)+1] = {
    P...
};

template struct EncryptImpl;

template 
struct EncryptImpl {
    static const char next = Head + Seed; // or whatever
    typedef typename EncryptImpl<
        typename B::template add_char::type,
        next, Tail...
    >::type type;
};

template struct EncryptImpl {
    typedef B type;
};

template struct Encrypt {
    typedef typename EncryptImpl, 0, P...>::type type;
};