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Language C++
(extreme template metaprogramming)
| Date: | 04/20/05 |
| Author: | Richard Wolf |
| URL: | n/a |
| Comments: | 5 |
| Info: | n/a |
| Score: |  (2.97 in 152 votes) |
/* Richard Wolf, 2002
99 bottles of beer on the wall in an extreme template-metaprogramming style.
It uses template specialisation to decided how to print numbers, whether
'bottles' should be plural, and to finish the song correctly.
Macros are used to generate the large number of specialisations required for
printing numbers nicely, eg 45 printed as "forty five" with pretty_print<45>().
Note that this will probably no compile immediately, since it requires the
compiler to instantiate templates to a depth of (number of bottles + 4).
Either reduce the number of starting bottles, or increase the maximum
template depth on your compiler.
Eg. using g++ use the -ftemplate-depth-103 command line option.
Tested on gcc, other compilers at your risk
*/
#include <iostream>
using namespace std;
template<bool small, int I>
struct pretty_printer;
#define SMALL_PRETTY_PRINTER(num, string) \
template<>\
struct pretty_printer<true, num>\
{\
static void print()\
{\
cout << string;\
}\
};
SMALL_PRETTY_PRINTER(0, "No")
SMALL_PRETTY_PRINTER(1, "One")
SMALL_PRETTY_PRINTER(2, "Two")
SMALL_PRETTY_PRINTER(3, "Three")
SMALL_PRETTY_PRINTER(4, "Four")
SMALL_PRETTY_PRINTER(5, "Five")
SMALL_PRETTY_PRINTER(6, "Six")
SMALL_PRETTY_PRINTER(7, "Seven")
SMALL_PRETTY_PRINTER(8, "Eight")
SMALL_PRETTY_PRINTER(9, "Nine")
SMALL_PRETTY_PRINTER(10, "Ten")
SMALL_PRETTY_PRINTER(11, "Eleven")
SMALL_PRETTY_PRINTER(12, "Twelve")
SMALL_PRETTY_PRINTER(13, "Thirteen")
SMALL_PRETTY_PRINTER(14, "Fourteen")
SMALL_PRETTY_PRINTER(15, "Fifteen")
SMALL_PRETTY_PRINTER(16, "Sixteen")
SMALL_PRETTY_PRINTER(17, "Seventeen")
SMALL_PRETTY_PRINTER(18, "Eighteen")
SMALL_PRETTY_PRINTER(19, "Nineteen")
#undef SMALL_PRETTY_PRINTER
template<int ones>
inline void
print_ones();
#define ONES_PRINTER(ones, string) \
template<> \
inline void \
print_ones<ones>() \
{\
cout << string;\
}
ONES_PRINTER(0, " ")
ONES_PRINTER(1, " one")
ONES_PRINTER(2, " two")
ONES_PRINTER(3, " three")
ONES_PRINTER(4, " four")
ONES_PRINTER(5, " five")
ONES_PRINTER(6, " six")
ONES_PRINTER(7, " seven")
ONES_PRINTER(8, " eight")
ONES_PRINTER(9, " nine")
#undef ONES_PRINTER
template<int tens>
inline void
print_tens();
#define TENS_PRINTER(tens, string) \
template<> \
inline void \
print_tens<tens>() \
{\
cout << string;\
}
TENS_PRINTER(2, "Twenty")
TENS_PRINTER(3, "Thirty")
TENS_PRINTER(4, "Forty")
TENS_PRINTER(5, "Fifty")
TENS_PRINTER(6, "Sixty")
TENS_PRINTER(7, "Seventy")
TENS_PRINTER(8, "Eighty")
TENS_PRINTER(9, "Ninety")
#undef TENS_PRINTER
template<int I>
struct pretty_printer<false, I>
{
static void print(){
print_tens<(I - I%10)/10>();
print_ones<(I%10)>();
}
};
template<int I>
void pretty_print()
{
pretty_printer<(I<20), I>::print();
}
template<int I>
inline void
BottlesOfBeer()
{
pretty_print<I>();
cout << " bottles of beer" ;
}
template<>
inline void
BottlesOfBeer<1>()
{
pretty_print<1>();
cout << " bottle of beer" ;
}
template<int I>
inline void
BottlesOfBeerOnTheWall()
{
BottlesOfBeer<I>();
cout << " on the wall";
}
template<int I>
inline void stanza()
{
BottlesOfBeerOnTheWall<I>();
cout << ",\n";
BottlesOfBeer<I>();
cout <<",\n";
}
template<int I>
inline void bridge()
{
cout << "Take one down, pass it around," << endl;
BottlesOfBeerOnTheWall<I-1>();
cout <<",\n";
}
template<>
inline void bridge<0>()
{
cout << "Go to the store and buy some more," << endl;
BottlesOfBeerOnTheWall<99>();
}
template<int I>
inline void verse()
{
stanza<I>();
bridge<I>();
}
template<int I>
inline void sing ()
{
verse<I>();
cout << endl;
sing<I-1>();
}
template<>
inline void sing<0> ()
{
verse<0>();
}
int main () {
sing<99>();
}
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Alternative Versions
| Version | Author | Date | Comments | Rate |
|---|---|---|---|---|
| object-oriented version | Tim Robinson | 04/20/05 | 4 | |
| hacking style | Tim Robinson | 04/20/05 | 14 | |
| meta programming | Arion Lei | 04/20/05 | 5 | |
| Preprocessor & self-include recursion | Chocapic | 02/27/07 | 6 | |
| feature creep | Jono | 04/27/09 | 1 | |
| most extreme template metaprogramming | Henrik Theiling | 12/04/11 | 0 | |
| 7 | Jono | 04/15/09 | 0 | |
| ob fuscated | Tapi (Paddy O'Brien) | 08/11/05 | 4 | |
| GUI version | Martyn Davies | 05/28/05 | 1 | |
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Comments
//___________________________________________
template <unsigned n>
inline void print_beer()
{
verse(n);
print_beer<n-1>();
}
template <>
inline void print_beer<0>()
{
verse(0);
print_beer<99>();
}
int main(int argc, char* argv[])
{
print_beer<99>();
return 0;
}
//___________________________________________
this worked very well, but i wanted to expand warehouse space to shelve 4 billion bottles, so i decided that approach was no longer ideal...
something with a recursive descent through significant places, now.. hmmm.... i'll be back!