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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: generic function and overloading
Newsgroups: comp.lang.ada
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Date: Thu, 18 Oct 2007 11:31:15 +0200
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Date: 2007-10-18T11:25:00+02:00
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On 18 Oct 2007 00:28:38 -0700, eliben wrote:

> I have a few "hardware" types, for example uint16 and uint32. And I
> want to write a functions that will set or clear bits of such types.
> For example:
> 
> function Bit_Set(word: uint16; bitn: natural) return uint16;
> 
> function Bit_Set(word: uint16; bitn: natural) return uint16 is
>   mask: uint16 := 2**bitn;
> begin
>   return word or mask;
> end Bit_Set;

Bit_Set (X, Natural'Last)?

> However, I realize that such a function would be almost completely
> duplicated for the uint32 type. In C++ I would probably define it as a
> template on the type of the word, and the compiler would do the job
> for me. In Ada, however, when using generics it doesn't seem I can
> leave the same function name for all types (as I would do in
> overloading). I can define a generic Bit_Set, but then I have to
> specialize it for uin16 and uint32 with different function names.

You can overload generic instances in exactly same way as you would other
subprograms:

generic
   type Data is mod <>;
   type Bit_No is range <>;
function Generic_Set_Bit (Word : Data; No : Bit_No) return Data;

function Generic_Set_Bit (Word : Data; No : Bit_No) return Data is
   pragma Assert (Data'Last = 2 ** Integer (Bit_No'Last + 1)  - 1);
begin
   return Word or 2 ** Integer (No);
end Generic_Set_Bit;

subtype Word_Index is Natural range 0..15;
function Set_Bit is
    new Generic_Set_Bit (Unsigned_16, Word_Index);

subtype Double_Word_Index is Natural range 0..31;
function Set_Bit is
    new Generic_Set_Bit (Unsigned_32, Double_Word_Index);

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