Debug help - Programming in D page 633 - concurrency shared(Exception) warnings

[Brother Bill]

If this technique is still valid, I need the code modernized so 
that it works without warnings.  I'm still in the D learning 
curve, so I don't quite know what is being warned, and how to 
clean up the mess.

I believe that the new code runs properly, but it would be nice 
for it to be 'warning free'.

The prior source/app.d which runs is
```
import std.stdio;
import std.concurrency;
import std.conv;

struct CalculationFailure
{
     string reason;
}

struct Exit
{
}

void calculate()
{
     bool isDone = false;

     while (!isDone)
     {
         receive((string message) {
             try
             {
                 ownerTid.send(to!double(message) + 0.5);
             }
             catch (Exception exc)
             {
                 ownerTid.send(CalculationFailure(exc.msg));
             }
         },
             (Exit message) { isDone = true; });
     }
}

void main()
{
     Tid calculator = spawn(&calculate);
     calculator.send("1.2");
     calculator.send("hello"); // ← incorrect input
     calculator.send("3.4");
     calculator.send(Exit());

     foreach (i; 0 .. 3)
     {
         writef("result %s: ", i);
         receive(
             (double message) { writeln(message); },

             (CalculationFailure message) {
             writefln("ERROR! '%s'", message.reason);
         });
     }
}

```

When run, this is the output:
```
result 0: 1.7
result 1: ERROR! 'no digits seen for input "hello".'
result 2: 3.9
```

The goal is to modify source/app.d so that it includes this 
snippet
```
// ... at the worker ...
  try {
     // ...
  } catch (shared(Exception) exc) {
     ownerTid.send(exc);
  }},

  // ... at the owner ...
  receive(
  // ...
     (shared(Exception) exc) {
        throw exc;
  });
```

The new merged source/app.d for main() is
```
void main()
{
     Tid calculator = spawn(&calculate);
     calculator.send("1.2");
     calculator.send("hello"); // ← incorrect input
     calculator.send("3.4");
     calculator.send(Exit());

     foreach (i; 0 .. 3)
     {
         writef("result %s: ", i);

		// ... at the owner ...
         receive(
             (double message) { writeln(message); },

             // (CalculationFailure message) {
             // 	writefln("ERROR! '%s'", message.reason);
         	// },

			(shared(Exception) exc) {
				throw exc;
			}
		);
     }
}
```

The console output is:
```
c:\dev\D\81 - 
90\c85_7d_exceptions_catch_send_exception_to_owner\source\app.d(26): Deprecation: can only catch mutable or const qualified types, not `shared(Exception)`
             catch (shared(Exception) exc)
             ^
c:\dev\D\81 - 
90\c85_7d_exceptions_catch_send_exception_to_owner\source\app.d(56): Deprecation: cannot throw object of qualified type `shared(Exception)`
                 throw exc;
                       ^
c:\dev\D\81 - 
90\c85_7d_exceptions_catch_send_exception_to_owner\source\app.d(26): Deprecation: can only catch mutable or const qualified types, not `shared(Exception)`
             catch (shared(Exception) exc)
             ^
c:\dev\D\81 - 
90\c85_7d_exceptions_catch_send_exception_to_owner\source\app.d(56): Deprecation: cannot throw object of qualified type `shared(Exception)`
                 throw exc;
                       ^
result 0: 1.7
result 1:
std.conv.ConvException at C:\D\dmd2\windows\bin64\..\..\src\phobos\std\conv.d(3360): no digits seen for input "hello".
```