Passing a reference to a returned reference

[Michael]

On Friday, 6 July 2018 at 14:50:39 UTC, Ali Çehreli wrote:
> On 07/06/2018 07:36 AM, Michael wrote:
> > but not in
> > my case, if this is a weird edge-case with setter member
> functions?
>
> This is all very interesting but I'm dying to see the code. :) 
> Can you change Timoses's code to demonstrate your case?
>
> Ali

I'm just trying to do that now.

Here is what I have in terms of code:

class Agent
{
     private
     {
         double[int] mDict;
     }

     // Setter: copy
     void beliefs(ref double[int] dict)
     {
         import std.stdio : writeln;
         writeln("Setter function.");
         this.mDict = dict;
     }

     // Getter
     auto ref beliefs()
     {
         return this.mDict;
     }
}

class Operator
{
     static auto ref create()
     {
         double[int] dict;
         dict[2] = 1.0;
         dict[1] = 0.0;
         return dict;
     }
}

unittest
{
     import std.stdio : writeln;

     Agent a = new Agent();

     a.beliefs = Operator.create();
     assert(a.beliefs.keys.length == 2);

     writeln(a.beliefs);
}


and here is the output WITH "ref" in beliefs's signature before 
double[int] dict:

➜  dempshaf git:(master) ✗ rdmd -I../ -unittest -main bug_test.d
[2:1, 1:0]

and without "ref":

➜  dempshaf git:(master) ✗ rdmd -I../ -unittest -main bug_test.d
Setter function.
[2:1, 1:0]


I'm surprised it's showing the correct value of the associative 
array, but hopefully this shows my point that it's not printing 
for some reason, when the parameter is ref.