D语言双向范围

import std.array; 
import std.stdio; 
import std.string; 

struct Reversed { 
   int[] range; 

   this(int[] range) { 
      this.range = range; 
   } 
   @property bool empty() const { 
      return range.empty; 
   }
   @property int front() const { 
      return range.back;  //  reverse 
   }
   @property int back() const { 
      return range.front; // reverse 
   } 
   void popFront() { 
      range.popBack(); 
   }
   void popBack() { 
      range.popFront(); 
   } 
} 

void main() { 
   writeln(Reversed([ 1, 2, 3])); 
}