Passing a string by reference

[Alexander Zhirov]

Do I understand correctly that in order for me to pass a string 
when creating an object, I must pass it by value? And if I have a 
variable containing a string, can I pass it by reference?

Should I always do constructor overloading for a type and a 
reference to it?
In the case of the variable `c`, a drop occurs. Why? An object is 
not being created on the stack?

```d
import std.stdio : writeln;

class A
{
     private string str = "base";

     this(ref string str)
     {
         writeln("type reference string");
         this.str = str;
     }

     this(string str)
     {
         writeln("type string");
         this.str = str;
     }

     this() {}

     void print()
     {
         writeln(str);
     }
}

void main()
{
     auto a = new A("Hello, World!"); // this type string
     a.print();
     string text = "New string";
     auto b = new A(text); // this type reference string
     b.print();
     A c;
     c.print();  // segmentation fault! Why not "base"?
}

```