SwitchOnString.cpp

// This file is to showcase the use of the relatively new constexpr keyword to
//   allow for processing of C-style strings at compile time.
// In turn, this allows for the use of C-style strings as cases in a switch
//   statement. This is something that is typically impossible as C-style strings
//   effectively degrade into void* in this situation as no string comparison
//   is normally possible.
// An example of why this would be useful would be in an assembler or other
//   simple language interpreter to improve interpretation time from O(n)
//   in an if {} else if {} chain to O(log(n)).
// Another benefit over using enums is the lowered reliance on consistancy across
//   multiple files. With this solution, enum definitions need not be created
//   updated to reflect the use in functions.
// A tradeoff, however, is the lack of transparancy. This can be positive or
//   negative, depending on the circumstance; an open-source project might require
//   more descriptive documentation to be available, but closed-source distributables
//   could keep more of their inner-workings private.

#include <iostream>
#include <string>

typedef char byte;

constexpr unsigned long long hashString(const byte* str)
{
  unsigned long long r = 1435958502956573194;
  // sdbm
  while (*str)
    r = *str++ + (r << 6) + (r << 16) - r;
  return r;
}

unsigned long long hashString(const std::string& str)
{
  return hashString(str.c_str());
}

int main()
{
  std::string input;
  std::cout << "Input string: ";
  std::cin >> input;
  std::cout << "You gave me: " << input << std::endl;
  std::cout << "Hash: " << hashString(input) << std::endl;

  switch (hashString(input))
  {
  case hashString("Hello"):
    std::cout << "Well, hi!" << std::endl;
    break;
  case hashString("Bye"):
    std::cout << "Oh, ok..." << std::endl;
    break;
  }

  return 0;
}