namespace hash {
    // generice type, no implementaion
    template<typename CharType> struct retval;
    // specialization for char
    template<>
    struct retval<char> {
        typedef char char_type;
        typedef unsigned long size_type;
        retval(size_type v=0) : v_(v) {}
        operator size_type () { return v_;}
        size_type v_;
    };
    template<>
    struct retval<wchar_t> {
        typedef wchar_t char_type;
        typedef unsigned long size_type;
        retval(size_type v=0) : v_(v) {}
        operator size_type () { return v_;}
        size_type v_;
    };
    // generic function, no implementation
    template<typename CharType> retval<CharType> hash_of(const CharType* s);
    // specialization for char
    // hash_of algorithm stolen from the immutable string suggestion.
    template<> retval<char> hash_of(const char* s)
    {
        unsigned long h = 0;
        for ( ; *s; ++s)
            h = 5*h + *s;
        return retval<char>(h);
    }
    // specialization for wchar_t
    template<> retval<wchar_t> hash_of(const wchar_t* s)
    {
        unsigned long h = 0;
        for ( ; *s; ++s)
            h = 5*h + *s;
        return retval<wchar_t>(h);
    }
    /* A recursive version could look like this
    inline unsigned long recursive_hash_of(const char* s, unsigned long
 h=0)
    {
        if (s == 0 || *s == '\0')
            return h;
        return recursive_hash_of(++s, 5*h + *s);
    }
    */
    // Compile time hash generation. Limit to 20 characher strings.
    // Would be nice to work with strings as template arguments
    // instead of single character template arguments.
    //
    template<const char C0, const char C1='\0', const char C2='\0', const
    char C3='\0',
    const char C4='\0', const char C5='\0', const char C6='\0',
    const char C7='\0', const char C8='\0', const char C9='\0',
    const char C10='\0', const char C11='\0', const char C12='\0',
    const char C13='\0', const char C14='\0', const char C15='\0',
    const char C16='\0', const char C17='\0', const char C18='\0',
    const char C19='\0', const char C20='\0'>
    struct Compile {
        template<const char c, unsigned long h>
        struct HashCalc {
            enum {
                value = c == 0 ? h : h*5 + c
            };
        };
        enum {
            hash = HashCalc<C20, HashCalc<C19, HashCalc<C18, HashCalc<C17,
            HashCalc<C16, HashCalc<C15, HashCalc<C14,
            HashCalc<C13,
            HashCalc<C12, HashCalc<C11, HashCalc<C10, HashCalc<C9,
            HashCalc<C8, HashCalc<C7, HashCalc<C6, HashCalc<C5,
            HashCalc<C4, HashCalc<C3, HashCalc<C2, HashCalc<C1,
            HashCalc<C0,
            0>::value>::value>::value>::value>::value>

            ::value>::value>::value>::value>::value>::value>::value>::value>

            ::value>::value>::value>::value>::value>::value>::value>::value
        };
    };
    template<const wchar_t C0, const wchar_t C1=L'\0', const wchar_t
    C2=L'\0', const wchar_t C3=L'\0',
    const wchar_t C4=L'\0', const wchar_t C5=L'\0', const wchar_t
    C6=L'\0',
    const wchar_t C7=L'\0', const wchar_t C8=L'\0', const wchar_t
    C9=L'\0',
    const wchar_t C10=L'\0', const wchar_t C11=L'\0', const wchar_t
    C12=L'\0',
    const wchar_t C13=L'\0', const wchar_t C14=L'\0', const wchar_t
    C15=L'\0',
    const wchar_t C16=L'\0', const wchar_t C17=L'\0', const wchar_t
    C18=L'\0',
    const wchar_t C19=L'\0', const wchar_t C20=L'\0'>
    struct CompileW {
        template<const wchar_t c, unsigned long h>
        struct HashCalc {
            enum {
                value = c == 0 ? h : h*5 + c
            };
        };
        enum {
            hash = HashCalc<C20, HashCalc<C19, HashCalc<C18, HashCalc<C17,
            HashCalc<C16, HashCalc<C15, HashCalc<C14,
            HashCalc<C13,
            HashCalc<C12, HashCalc<C11, HashCalc<C10, HashCalc<C9,
            HashCalc<C8, HashCalc<C7, HashCalc<C6, HashCalc<C5,
            HashCalc<C4, HashCalc<C3, HashCalc<C2, HashCalc<C1,
            HashCalc<C0,
            0>::value>::value>::value>::value>::value>

            ::value>::value>::value>::value>::value>::value>::value>::value>

            ::value>::value>::value>::value>::value>::value>::value>::value
        };
    };
} // namespace hash
int main(int argc, char* argv[])
{
    printf("Hash testing!\n");
    using namespace hash;
    unsigned long u = hash_of("testing");
    printf("hash_of: %u\n", u);
    u = hash_of(L"testing");
    printf("hash_of: %u\n", u);
    typedef Compile<'t','e','s','t', 'i', 'n', 'g' > ATesting;
    printf("hash: %u\n", ATesting::hash );
    typedef CompileW<L't',L'e',L's',L't', L'i', L'n', L'g' > WTesting;
    printf("hash: %u\n", WTesting::hash );
    // compile time error if duplicate case entries are generated
    switch (hash_of("/print")) {
    case Compile<'/','n','e','w'>::hash:
        printf("/new option\n");
        break;
    case Compile<'/','o','p','e','n'>::hash:
        printf("/open option\n");
        break;
    case Compile<'/','p','r','i','n','t'>::hash:
        printf("/print option\n");
        break;
    }
    return 0;
}

#include <boost/mpl/string.hpp>
#include <boost/mpl/fold.hpp>
#include <boost/mpl/size_t.hpp>
namespace meta
{
#pragma warning(push)
// disable addition overflow warning
#pragma warning(disable:4307)
template <typename Seed, typename Value>
struct hash_combine
{
  typedef mpl::size_t<
    Seed::value ^ (static_cast<std::size_t>(Value::value)
      + 0x9e3779b9 + (Seed::value << 6) + (Seed::value >> 2))
  > type;
};
#pragma warning(pop)
// Hash any sequence of integral wrapper types
template <typename Sequence>
struct hash_sequence
  : mpl::fold<
        Sequence
      , mpl::size_t<0>
      , hash_combine<mpl::_1, mpl::_2>
    >::type
{};
// For hashing std::strings et al that don't include the zero-terminator
template <typename String>
struct hash_string
  : hash_sequence<String>
{};
// Hash including terminating zero for char arrays
template <typename String>
struct hash_cstring
  : hash_combine<
        hash_sequence<String>
      , mpl::size_t<0>
    >::type
{};
} // namespace meta</code></pre>

switch (boost::hash_value("bunnies"))
{
case meta::hash_cstring< mpl::string<'bunn','ies'> >::value:
  std::cout << "bunnies!\n";
  break;
case meta::hash_cstring< mpl::string<'bear','s'> >::value:
  std::cout << "bears!\n";
  break;
default:
  std::cout << "no hash matched\n";
}