Re: I need a little help - it's been a long time - with enumeration type and for use representation

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 13 Nov 2009 08:03:23 -0800 (PST), Harry Tucker wrote:

> I have a piece of data which represents a enumeration as a hexadecimal
> value. It is a bit field but I see the data most usefull as an
> enumeration. for example in the CSV file the data is represented as
> '0x1'. So I defined the enum as:
> 
> <code>
>    type Spell_School_Type is (
>       UNKNOWN,
>       PHYSICAL,
>       HOLY,
>       FIRE,
>     ...
> </code>
> 
> And since the data has a value I use a represetation clause as:
> <code>
>    for Spell_School_Type use
>      (UNKNOWN     => 2#0000_0000#,
>       PHYSICAL      => 2#0000_0001#,
>       HOLY             => 2#0000_0010#,
>       FIRE              => 2#0000_0100#,
>     ...
> </code>

For bit fields modular types are better:

   type Spell_School_Type is mod 2**3;
       -- 3 is the number of independent bits
   Unknown  : constant Spell_School_Type := 0;
   Physical : constant Spell_School_Type := 2**0;
   Holy     : constant Spell_School_Type := 2**1;
   Fire     : constant Spell_School_Type := 2**2;
   Any    : constant Spell_School_Type := Spell_School_Type'Last;

> Is the best way to parse the raw info (i.e. 0x1)  into the enumeration
> (i.e PHYSICAL) to use a if/elsif and assign the enum position or is
> there an attribute which works best.

You parse "0x", then you do a hexadecimal number following it, then you
pass that number (x) to:

   Spell_School_Type'Val (x)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de