Re: 'Size hack for enumerated types

[Victor Porton <porton@narod.ru>]

Victor Porton wrote:

> Victor Porton wrote:
> 
>> I tried to implement it in a memory savvy way. But GNAT does not compile
>> it. It would be good if a future version of Ada supported it.
>> 
>> -- rds.ads
>> package RDF is
>> end RDF;
>> 
>> -- rdf-auxilary.ads
>> with Interfaces.C;
>> 
>> package RDF.Auxilary is
>> 
>>    generic
>>       type Enum_Type is range <>;
>>    package Convert_Enum is
>>       function To_C(Argument: Enum_Type) return Interfaces.C.int;
>>       function From_C(Argument: Interfaces.C.int) return Enum_Type;
>>    end;
>> 
>> end RDF.Auxilary;
>> 
>> -- rdf-auxilary.adb
>> with Ada.Unchecked_Conversion;
>> 
>> package body RDF.Auxilary is
>> 
>>    package body Convert_Enum is
>>       
>>       type Small is mod 2**(Enum_Type'Size);
> 
> Sorry, need also multiply with byte size in bits. BTW, how to get it?
> 
>>       function To_C_Internal is
>>         new Ada.Unchecked_Conversion (Source => Enum_Type, Target =>
>>         Small);
>> 
>>       function From_C_Internal is
>>         new Ada.Unchecked_Conversion (Source => Small, Target =>
>>         Enum_Type);
>>       
>>       function To_C(Argument: Enum_Type) return Interfaces.C.int is
>>       begin
>>          return Interfaces.C.int(To_C_Internal(Argument));
>>       end;
>>             
>>       function From_C(Argument: Interfaces.C.int) return Enum_Type is
>>       begin
>>          return From_C_Internal(Small(Argument));
>>       end;
>> 
>>    end;
>> 
>> end RDF.Auxilary;
>> 
>> gnatmake -q -c -gnatc -u -P/home/porton/Projects/redland-
>> bindings/ada/test.gpr -XRUNTIME=full -XMODE=Install rdf-auxilary.adb
>> rdf-auxilary.adb:7:25: non-static expression used for modular type bound
>> rdf-auxilary.adb:7:38: size attribute is only static for static scalar
>> type (RM 4.9(7,8))
>> gnatmake:
>> "/home/porton/Projects/redland-bindings/ada/src/rdf-auxilary.adb"
>> compilation error

I think this can be made manually (without generics) (explicitly declaring a 
`Small` type for every enumeration in question), but I better do it with 
'Size hack, not spending time on manually programming what should be doable 
with generics.

-- 
Victor Porton - http://portonvictor.org