Why do immutable variables need reference counting?

[Salih Dincer]

On Monday, 11 April 2022 at 21:48:56 UTC, Ali Çehreli wrote:
> On 4/11/22 08:02, Paul Backus wrote:
>
> > any pointers or references
>
> To add, Salih and I were in an earlier discussion where that 
> concept appeared as "indirections."
>
> Ali

I tried the following and I didn't understand one thing: Why is 
there no need to use dup when slicing?

```d
struct S(T) {
  T fileName;

   this(T fileName) {
     this.fileName = fileName;
     report();
   }

   ~this() { report(); }

   void report(string func = __FUNCTION__) {
     import std.stdio;
     writefln!"%s\nworking with %s"(func, fileName);
   }
}
alias T1 = const(char)[];
alias T2 = const char[];
alias T3 = const(char[]); // T3 == T2
alias T4 = immutable char[]; // Not compiling!


void main() {
   auto fileName = "foo.txt".dup;
   auto s = S!T1(fileName);
   fileName[0..3] = "bar";
}/* Results:
   *
   *T1:
   *
   source.S!(const(char)[]).S.this
   working with foo.txt.
   source.S!(const(char)[]).S.~this
   working with bar.txt.
   *
   *T2:
   *
   source.S!(const(char[])).S.this
   working with foo.txt
   source.S!(const(char[])).S.~this
   working with bar.txt
   *
   *T3:
   *
   source.S!(const(char[])).S.this
   working with foo.txt
   source.S!(const(char[])).S.~this
   working with bar.txt
   *
   *T4
   *
   Error: slice `fileName[0..3]` is not mutable
   */
```

SDB at 79