Re: Some kind of repeating in Static_Predicate

["Randy Brukardt" <randy@rrsoftware.com>]

"ytomino" <aghia05@gmail.com> wrote in message 
news:675621d4-7f23-48bd-a7e0-4105b21ddfd7@googlegroups.com...
> On Tuesday, June 5, 2018 at 6:33:48 AM UTC+9, Randy Brukardt wrote:
...
>> > Thanks. But I want to separate the table and the subtype...
>>
>> That seems backwards to me. You are wanting to declare a set subtype, and
>> Ada uses the silly static predicate for doing so rather than having a 
>> proper
>> set constraint. Either way, that's a subtype declaration.
>>
>> So the operative thing here is the subtype. There's no "table" in a set
>> description. If you need to check membership in the set, you just do that
>> with "in".
>>
>> Thus:
>>
>>     subtype T is Character
>>        with Static_Predicate => (T in 'T' | 'a' | 'b' | 'l' | 'e');
>>
>>     if Param in T then ...
>>
>> If you really needed a table, I'd construct that from the set. (But I 
>> can't
>> imagine what the use would be, certainly in cases like the "separators"
>> definition you showed in another mail.)
>
> Thanks. I understood it's backwards.
> Yes, the table is needless in run-time. I want only compile-time checking
>by Static_Predicate in this case. Also, types should be more primary than
>constants basically.
> However, a subtype declaration can't be separated to another package...

Of course a subtype can be declared in another package, I'm not sure why you 
say that. For subtypes, you can always declare another subtype in your 
primary package to get visibility:

    package Params is
        subtype Separators is Character with Static_Predicate => Separators 
in '/' | '\';
        -- other configuation parameters here.
   end Params;

   with Params;
   package File_Ops is
       subtype Separators is Params.Separators;
       -- Other file operations here.
   end File_Ops;

(Using the same exact name isn't a good idea if you are the sort to stick 
use clauses everywhere,but of course the names don't have to be identical.) 
Also note that "use type" and "use all type" will give you appropriate 
visibility on the operators (and primitive operations, in the case of "use 
all type") regardless of where the type is declared - another reason to 
prefer "use type" when possible.

>The table may be configured before compiling, like the example of directory
>separators.

Yes, see above.

                              Randy.