Passing a string by reference

[Hipreme]

On Tuesday, 8 November 2022 at 12:30:50 UTC, Alexander Zhirov 
wrote:
> 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"?
> }
>
> ```


You forgot to assign "c" to anything, I think you meant:
`A c = b;`
Read that segmentation fault as null pointer exception.

Whenever you assign something to `ref type something`, it will 
basically be the same as writing `myVariable = *something;` in C 
code, so, in that case, it won't make any difference.

     The `ref` attribute only means that if you change your string 
inside the code that takes by ref, it will reflect when 
returning, such as:
     ```d
     void modifyString(ref string input)
     {
        input~= "Now it is modified";
     }
     string text = "New string";
     modifyString(text);
     writeln(text); //"New stringNow it is modified"
     ```