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From: Victor Porton <porton@narod.ru>
Newsgroups: comp.lang.ada
Subject: Re: 'Size hack for enumerated types
Date: Sun, 06 Jul 2014 01:23:07 +0300
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Date: 2014-07-06T01:23:07+03:00
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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
> 
> 
-- 
Victor Porton - http://portonvictor.org