Interesting rant about Scala's issues

[Paulo Pinto]

Using Ada code examples below:

On Monday, 7 April 2014 at 16:25:45 UTC, Regan Heath wrote:
> On Mon, 07 Apr 2014 16:15:41 +0100, Paulo Pinto 
> <pjmlp at progtools.org> wrote:
>
>> Am 07.04.2014 12:07, schrieb Regan Heath:
>>> On Mon, 07 Apr 2014 00:17:45 +0100, Andrei Alexandrescu
>>> <SeeWebsiteForEmail at erdani.org> wrote:
>>>
>>>> On 4/6/14, 10:52 AM, Walter Bright wrote:
>>>>> On 4/6/2014 3:31 AM, Leandro Lucarella wrote:
>>>>>> What I mean is the current semantics of enum are as they 
>>>>>> are for
>>>>>> historical reasons, not because they make (more) sense 
>>>>>> (than other
>>>>>> possibilities). You showed a lot of examples that makes 
>>>>>> sense only
>>>>>> because you are used to the current semantics, not because 
>>>>>> they are the
>>>>>> only option or the option that makes the most sense.
>>>>>
>>>>> I use enums a lot in D. I find they work very 
>>>>> satisfactorily. The way
>>>>> they work was deliberately designed, not a historical 
>>>>> accident.
>>>>
>>>> Sorry, I think they ought to have been better. -- Andrei
>>>
>>> Got a DIP/spec/design to share?
>>>
>>> R
>>>
>>
>> How they work in languages like Ada.
>
> Ok, brief look at those shows me enums can be converted to a 
> "Pos" index but otherwise you cannot associate a numberic value 
> with them, right?
>
> So if we had that in D, Walters examples would look like..
>
> 1)
>
>   enum Index { A, B, C }
>   T[Index.C.pos + 1] array; // perhaps?


type Index is (A, B, C);

d_array: array Index'Length of T;


>   ...
>   array[Index.B.pos] = t;   // yes?

d_array(Index'Pos(B)) := t;

>
> 2)
>
>   array[Index.A.pos + 1] = t; // yes?

d_array(Index'Succ(A)) := t;

>
> 3)
>
>   enum Mask { A=1,B=4 } // not possible?
>
>   Mask m = A | B;   // Error: incompatible operator | for enum


type Mask is (A, B);
for Mask use (A => 1, B => 4);

m : Mask := Mask'Pos(A) or Mask'Pos(B);

>
>
> Have I got that right?
>
> For a proposal like this to even be considered I would imagine 
> it would have to be backward compatible with existing uses, so 
> you would have to be proposing a new keyword or syntax on 
> "enum" to trigger typesafe enums, perhaps "typesafe" is a good 
> keyword, e.g.
>
> typesafe enum Index { A, B, C } // requires use of .pos to 
> convert to int 0, 1, or 2.
> enum Index { A, B, C }          // existing pragmatic behaviour
>
> R


This is the C++ approach with enum class for strong typed enums.