C++11 N2765: user-defined literals

C++11 will have tons of new features and concepts. One among them is
N2765: user-defined literals (scheduled for GCC 4.7). Quite possible I'm dumb
and ugly, but frankly, "user-defined literals" is something I've so many doubts
about. There're already lots of examples, though I haven't seen anything really
neat so far (only speaking for myself).


For example:

constexpr long double operator"" _degrees (long double d)
{
        return d * 0.0175;
}

long double pi = 180_degrees;

Or (link)

typedef std::map MyMap;
MyMap create_map()
{
    MyMap m;
    m["lol"] = 7;
    return m;
}

auto m = create_map();

int& operator "" m(const char *key, size_t length)
{
        return m[key];
}

int main(void)
{
    std::cout << "lol"m << std::endl;
    // 7
    "lol"m = 2;
    std::cout << "lol"m << std::endl;
    // 2
    return 0;
}


Or (link)

template struct __checkbits
{
    static const bool valid = false;
};

template struct __checkbits
{
    static const bool valid = (High == '0' || High == '1')
                   && __checkbits::valid;
};

template struct __checkbits
{
    static const bool valid = (High == '0' || High == '1');
};

template
  inline constexpr std::bitset
  operator"" _bits() noexcept
{
    static_assert(__checkbits::valid, "invalid digit in binary string");
    return std::bitset((char []){Bits..., '\0'});
}

int main()
{
  auto bits = 010101010101010101010101010101010101010101_bits;
  std::cout << bits << std::endl;
  std::cout << "size = " << bits.size() << std::endl;
  std::cout << "count = " << bits.count() << std::endl;
  std::cout << "value = " << bits.to_ullong() << std::endl;

  //  This triggers the static_assert at compile time.
  auto badbits = 21010101010101010101010101010101010101_bits;

  //  This throws at run time.
  std::bitset<64> badbits2("21010101010101010101010110101010101_bits");
}


-ss