D语言无限随机访问范围

import std.array; 
import std.stdio; 
import std.string; 
import std.range; 
import std.algorithm; 

class SquaresRange { 
   int first;  
   this(int first = 0) { 
      this.first = first; 
   }
   enum empty = false; 
   @property int front() const { 
      return opIndex(0); 
   }
   void popFront() { 
      ++first; 
   }
   @property SquaresRange save() const { 
      return new SquaresRange(first); 
   }
   int opIndex(size_t index) const { 
      /* This function operates at constant time */ 
      immutable integerValue = first + cast(int)index; 
      return integerValue * integerValue; 
   } 
}

bool are_lastTwoDigitsSame(int value) { 
   /* Must have at least two digits */ 
   if (value < 10) { 
      return false; 
   } 

   /* Last two digits must be divisible by 11 */ 
   immutable lastTwoDigits = value % 100; 
   return (lastTwoDigits % 11) == 0; 
} 

void main() { 
   auto squares = new SquaresRange(); 

   writeln(squares[5]);

   writeln(squares[10]); 

   squares.popFrontN(5); 
   writeln(squares[0]); 

   writeln(squares.take(50).filter!are_lastTwoDigitsSame); 
}