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  1. /// "Each with each other" random range
  2. module eerange.randomrange;
  3.  
  4. import std.traits;
  5. import std.stdio; //FIXME: remove
  6.  
  7. @safe:
  8. //@nogc: //FIXME: enable
  9.  
  10. ///
  11. struct EachWithEachOtherRandomAccessRange(R)
  12. {
  13.     private R srcRange;
  14.     const size_t squareWidth;
  15.  
  16.     ///
  17.     this(R r)
  18.     {
  19.         srcRange = r;
  20.         squareWidth = srcRange.length + 1;
  21.     }
  22.  
  23.     ///
  24.     size_t length() const
  25.     {
  26.         const len = srcRange.length;
  27.  
  28.         return (len * len - len) / 2;
  29.     }
  30.  
  31.     private static struct Coords
  32.     {
  33.         size_t x;
  34.         size_t y;
  35.     }
  36.  
  37.     private Coords coordsInSquare(size_t idx)
  38.     {
  39.         Coords ret;
  40.         ret.x = idx % squareWidth;
  41.         ret.y = idx / squareWidth;
  42.  
  43.         return ret;
  44.     }
  45.  
  46.     private auto getElemBySquareCoords(Coords c)
  47.     {
  48.         // elements shifted relative to entire square
  49.         c.x -= 1; // elements shifted relative to entire square
  50.         //~ c.y -= 1; // elements shifted relative to entire square
  51.         writeln(c);
  52.         return [srcRange[c.x], srcRange[c.y]]; // TODO: replace by static array?
  53.     }
  54.  
  55.     ///
  56.     auto opIndex(const size_t idx)
  57.     {
  58.         assert(idx < length);
  59.  
  60.         Coords coords = coordsInSquare(idx);
  61.  
  62.         if(coords.x <= coords.y) // under diagonal line?
  63.         {
  64.             const latestIdx = srcRange.length;
  65.  
  66.             // Mirroring coords
  67.             coords.x = latestIdx - coords.x;
  68.             coords.y = latestIdx - coords.y - 1; // shifted above diagonal
  69.         }
  70.  
  71.         return getElemBySquareCoords(coords);
  72.     }
  73. }
  74.  
  75. ///
  76. auto eeRandomRange(T)(T inputRange)
  77. {
  78.     return EachWithEachOtherRandomAccessRange!(T)(inputRange);
  79. }
  80.  
  81. unittest
  82. {
  83.     import std.range.primitives;
  84.  
  85.     //~ static assert(isRandomAccessRange!(EachWithEachOtherRandomAccessRange!(int[])));
  86. }
  87.  
  88. unittest
  89. {
  90.     import std.parallelism;
  91.     import std.algorithm.searching: count;
  92.  
  93.     int[] arr = [0, 1, 2, 3];
  94.  
  95.     auto r = arr.eeRandomRange;
  96.  
  97.     size_t cnt;
  98.  
  99.     foreach(i; 0 .. r.length)
  100.     {
  101.         writeln("i=", i);
  102.  
  103.         auto unused = r[i];
  104.  
  105.         cnt++;
  106.     }
  107.  
  108.     //~ auto mapped = taskPool.amap!((a){ return a; } )(r);
  109.  
  110.     assert(cnt == 6);
  111.     assert(arr.eeRandomRange.length == 6);
  112. }
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