D语言结构体作为函数参数

import std.stdio;

struct Books { 
   char [] title; 
   char [] author; 
   char [] subject; 
   int   book_id; 
}; 

void main( ) { 
   Books Book1;        /* Declare Book1 of type Book */ 
   Books Book2;        /* Declare Book2 of type Book */  

   /* book 1 specification */ 
   Book1.title = "D Programming".dup; 
   Book1.author = "Raj".dup; 
   Book1.subject = "D Programming Tutorial".dup; 
   Book1.book_id = 6495407;  

   /* book 2 specification */ 
   Book2.title = "D Programming".dup; 
   Book2.author = "Raj".dup; 
   Book2.subject = "D Programming Tutorial".dup; 
   Book2.book_id = 6495700;  

   /* print Book1 info */ 
   printBook( Book1 );  

   /* Print Book2 info */ 
   printBook( Book2 );  
}

void printBook( Books book ) { 
   writeln( "Book title : ", book.title); 
   writeln( "Book author : ", book.author); 
   writeln( "Book subject : ", book.subject); 
   writeln( "Book book_id : ", book.book_id); 
}