Integer'Class

Integer'Class

[Rick Santa-Cruz]

Hi,

sorry for so many questions.... maybe that's easy to answer, but I don't 
find any senseful answer to that:
Why can't I use: Integer'Class, but I can derive a new class from Integer in 
writing:
type New_Int is new Integer range 1..100;

Isn't this unlogical? Or have I missunderstand something completly?

Thanks tons,
A becoming desperated Rick 

Re: Integer'Class

[Jeffrey Carter]

Rick Santa-Cruz wrote:

> Why can't I use: Integer'Class, but I can derive a new class from
> Integer in writing:
> type New_Int is new Integer range 1..100;
> 
> Isn't this unlogical? Or have I missunderstand something completly?

It is inconsistent. 'Class only applies to tagged types.

This is compounded further by the discussion of type classes, such as 
the class of integer types, floating-point types, and so on. 'Class was 
introduced in Ada 95 to allow OOP; type classes existed in Ada 83.

-- 
Jeff Carter
"You tiny-brained wipers of other people's bottoms!"
Monty Python & the Holy Grail
18

Re: Integer'Class

[Rick Santa-Cruz]

"Jeffrey Carter" <spam@spam.com> schrieb im Newsbeitrag 
news:hfm8d.2844$UP1.1203@newsread1.news.pas.earthlink.net...
> Rick Santa-Cruz wrote:
>
>> Why can't I use: Integer'Class, but I can derive a new class from
>> Integer in writing:
>> type New_Int is new Integer range 1..100;
>>
>> Isn't this unlogical? Or have I missunderstand something completly?
>
> It is inconsistent. 'Class only applies to tagged types.
>
> This is compounded further by the discussion of type classes, such as the 
> class of integer types, floating-point types, and so on. 'Class was 
> introduced in Ada 95 to allow OOP; type classes existed in Ada 83.
So, it's only a notation-problem and I am not only using "new" to derive (in 
the conext of OOP) from a type? If this is the case, I can use the 
new-keyword always and not only in cases of tagged types... is this true?

Bye,
Rick 

Re: Integer'Class

[Martin Krischik]

Rick Santa-Cruz wrote:

> Hi,
> 
> sorry for so many questions.... maybe that's easy answer, but I don't
> find any senseful answer to that:
> Why can't I use: Integer'Class, but I can derive a new class from Integer
> in writing:
> type New_Int is new Integer range 1..100;

> Isn't this unlogical? Or have I missunderstand something completly?

'Class is the tag of OO-classes. In C++ talk: virtual function table and
RTTI rolled in one. 

The parent for simple types is 'Base. The 'Base of Integer is
universal_integer - a compiler internal type which cannot be used directly.

Saying that, I now start to wonder what 'Base of a tagged type is...

With Regards

Martin

-- 
mailto://krischik@users.sourceforge.net
http://www.ada.krischik.com

Re: Integer'Class

[Christoph Karl Walter Grein]

There are several mistakes in the post:

> The parent for simple types is 'Base. The 'Base of Integer is
> universal_integer - a compiler internal type which cannot be used directly.
> 
> Saying that, I now start to wonder what 'Base of a tagged type is...

'Base is defined for scalar subtypes only. So there is no such thing for tagged types.

Integer is the "first subtype" (constrained) of an anomymous unconstrained base type
accessible via the 'Base attribute.

The parent of all integer types is root integer, which again is anonymous. All integer
literals are of this type; they are implicitly converted to the correct target type.
You may informally think of root integer as Integer'Class.
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Re: Integer'Class

[Dmitry A. Kazakov]

On Tue, 5 Oct 2004 02:10:55 +0200, Rick Santa-Cruz wrote:

> sorry for so many questions.... maybe that's easy to answer, but I don't 
> find any senseful answer to that:
> Why can't I use: Integer'Class, but I can derive a new class from Integer in 
> writing:
> type New_Int is new Integer range 1..100;
> 
> Isn't this unlogical? Or have I missunderstand something completly?

Not at all. It is quite logical, all types should have T'Class, (probably
T'Class ones too (:-)). But when Ada 83 was extended to Ada 95, a decision
was taken not to go that far. I suppose, because the amount of changes
needed was considered too large. So only tagged types may be grouped in
classes, presently. Constructors/destructors were implemented as a hack
etc. Alas.

As for New_Int, it is not just deriving from Integer. It is something like:

-- This is not Ada!
type <Anonymous_Subtype> is -- Deriving a subtype
   new Integer
      with null record              -- No extension
      with constraint range 1..100; -- Constraint on the values
type New_Int is new <Anonymous_Subtype>; -- Cloning the subtype

The result is a clone of a subtype of Integer. It is an unrelated to
Integer type. Therefore it cannot be put into Integer'Class, it induces a
class of its own. A related construct is:

subtype Sub_Int is Integer range 1..100;

This only puts a constraint, but produces no true new type. So you cannot
override Integer operations in Sub_Int, only overload (with nasty
consequences). This is a heavy heritage of Ada 83, which considered all
subtypes as constrained bases.

I do hope that Ada 2010 will have T'Class for all specific types, let's
see.

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

Re: Integer'Class

[Jeffrey Carter]

Rick Santa-Cruz wrote:

> So, it's only a notation-problem and I am not only using "new" to
> derive (in the conext of OOP) from a type? If this is the case, I can
> use the new-keyword always and not only in cases of tagged types...
> is this true?

I'm not sure what you're asking. You can derive from any type, but 
usually you neither want or need to.

-- 
Jeff Carter
"We burst our pimples at you."
Monty Python & the Holy Grail
16

Re: Integer'Class

[Jeffrey Carter]

Martin Krischik wrote:

> The parent for simple types is 'Base. The 'Base of Integer is 
> universal_integer - a compiler internal type which cannot be used
> directly.

No, the 'Base of Integer is Integer'Base, which is usually identical to 
Integer. Universal_Integer and Root_Integer are different concepts, and 
not normally a concern for a beginner.

-- 
Jeff Carter
"We burst our pimples at you."
Monty Python & the Holy Grail
16