蔡逸竹

為什麼說是測試「編譯器」的功力呢？因為這個程式用到了一些高階的 template 功能，並不是所有 compiler 都支援。如果您手上的編譯器是 VC6 的話，請去 Program Files 底下把它拖曳進資源桶，然後改用 dev-c++（它使用 GCC 3.4.2）。使用 GCC 4.1.1（我是用這個編譯、測試的）是完全沒有問題的

本來想稍微講解，可是想想又覺得沒什麼好說的，畢竟只是無聊的小作業 = = 以下附上程式碼！

引用:

/*
* Meta-programming Infrastructure
*/

struct NullType { };

template <typename Head, typename Tail>
struct Typelist { };

/**
* meta-(data structure) to store "X x Y = Z"
*/

template <unsigned int X, unsigned int Y>
struct ChartNode
{
enum { first = X, second = Y, product = X * Y };
};

/**
* Chart Maker...
*
* @param X, Y: current X and Y
* @param XN, YN: max X and Y
*/

template <unsigned int X, unsigned int Y, unsigned int XN, unsigned int YN>
struct makeChart
{
typedef Typelist< ChartNode<X, Y>, typename makeChart<X+1, Y, XN, YN>::Result > Result;
};

template <unsigned int Y, unsigned int XN, unsigned int YN>
struct makeChart<XN, Y, XN, YN>
{
typedef Typelist< ChartNode<XN, Y>,
  Typelist< NullType, typename makeChart<1, Y+1, XN, YN>::Result > > Result;
};

template <unsigned int XN, unsigned int YN>
struct makeChart<XN, YN, XN, YN>
{
typedef Typelist< ChartNode<XN, YN>, NullType > Result;
};

/**
* Algorithm to write a ChartNodeList to an Ostream
*/
template <typename TList>
struct toOstream;

template <typename X, typename XS>
struct toOstream< Typelist<X, XS> > : toOstream< XS >
{
template <typename OST, typename DELIM>
OST & operator() (OST & dest, DELIM delim1, DELIM delim2)
{
  dest << X::first << "x" << X::second << "=" << X::product << delim1;
  return toOstream<XS>:perator()(dest, delim1, delim2);
}
};

template <typename XS>
struct toOstream< Typelist<NullType, XS> > : toOstream< XS >
{
template <typename OST, typename DELIM>
OST & operator() (OST & dest, DELIM delim1, DELIM delim2)
{
  dest << delim2;
  return toOstream<XS>:perator()(dest, delim1, delim2);
}
};

template <>
struct toOstream<NullType>
{
template <typename OST, typename DELIM>
OST & operator() (OST & dest, DELIM, DELIM delim2)
{
  dest << delim2;
  return dest;
}
};

/*
* Main Program...
*/
#include <iostream>
#include <iterator>
using namespace std;

int main()
{
enum { x = 9, y = 9 };
cout << "make a Chart from [(1x1=1) .. (" << x << "x" << y << "=" << x*y << ")]:" << endl;

typedef makeChart<1, 1, x, y>::Result ChartList;
toOstream<ChartList> generator;
generator(cout, ", ", "\n");

return 0;
}
--------------------------------------------------------------------------------

整個演算法包裝成一系列的 template objects，最後再丟給 toOstream<> 這個唯一有被具現化的 template object，其他程式碼全部都在編譯時期被展開了！帶入 x = 9, y = 9 的結果：

引用:

$ ./ninenine
make a Chart from [(1x1=1) .. (9x9=81)]:
1x1=1, 2x1=2, 3x1=3, 4x1=4, 5x1=5, 6x1=6, 7x1=7, 8x1=8, 9x1=9,
1x2=2, 2x2=4, 3x2=6, 4x2=8, 5x2=10, 6x2=12, 7x2=14, 8x2=16, 9x2=18,
1x3=3, 2x3=6, 3x3=9, 4x3=12, 5x3=15, 6x3=18, 7x3=21, 8x3=24, 9x3=27,
1x4=4, 2x4=8, 3x4=12, 4x4=16, 5x4=20, 6x4=24, 7x4=28, 8x4=32, 9x4=36,
1x5=5, 2x5=10, 3x5=15, 4x5=20, 5x5=25, 6x5=30, 7x5=35, 8x5=40, 9x5=45,
1x6=6, 2x6=12, 3x6=18, 4x6=24, 5x6=30, 6x6=36, 7x6=42, 8x6=48, 9x6=54,
1x7=7, 2x7=14, 3x7=21, 4x7=28, 5x7=35, 6x7=42, 7x7=49, 8x7=56, 9x7=63,
1x8=8, 2x8=16, 3x8=24, 4x8=32, 5x8=40, 6x8=48, 7x8=56, 8x8=64, 9x8=72,
1x9=9, 2x9=18, 3x9=27, 4x9=36, 5x9=45, 6x9=54, 7x9=63, 8x9=72, 9x9=81,