D语言字符大小写

import std.stdio;
import std.string;

void main() { 
   char[] s1 = "hello World ".dup; 
   writeln("Capitalized string of s1 is ",capitalize(s1)); 

   writeln("Uppercase string of s1 is ",toUpper(s1)); 

   writeln("Lowercase string of s1 is ",toLower(s1));   
}