D语言输入范围

import std.stdio; 
import std.string; 

struct Student { 
   string name; 
   int number; 

   string toString() const { 
      return format(%s(%s), name, number); 
   } 
}

struct School { 
   Student[] students; 
}
struct StudentRange {
   Student[] students; 

   this(School school) { 
      this.students = school.students; 
   } 
   @property bool empty() const { 
      return students.length == 0; 
   } 
   @property ref Student front() { 
      return students[0]; 
   } 
   void popFront() { 
      students = students[1 .. $]; 
   } 
}

void main() { 
   auto school = School([ Student(Raj, 1), Student(John, 2), Student(Ram, 3)]);
   auto range = StudentRange(school); 
   writeln(range);  

   writeln(school.students.length);

   writeln(range.front); 

   range.popFront;  

   writeln(range.empty); 
   writeln(range); 
}