Re: Ada 200X

["Robert I. Eachus" <rieachus@attbi.com>]

Larry Kilgallen wrote:

> I am not the original poster, but the case where I find this troublesome
> is trying to replace a method for a parent type with enhanced code to:
> 
>         1. Do something special
> 
>         2. Do whatever the method for the parent type would do
> 
>         3. Do something else special
> 
> The lack of a construct to specify "corresponding method of ancestor"
> seems to me to be what breaks information hiding.

Oh, that is so easy that I never thought of people having problems with 
it.  I'll give an example:

type Foo is tagged...

procedure Bar(F: in out Foo);
...

type New_Foo is new Foo with...

procedure Bar(F: in out New_Foo);
...

procedure Bar(F: in out New_Foo) is
begin
    Do(Something_Special);
    Bar(Foo(F)); -- view conversion
    Do(Something_Else_Special);
end Bar;

The view conversion passes the Foo part of a New_Foo object to the 
parent Bar by reference.  So the parent operation only sees the parts of 
the New_Foo object that it knows about.  When writing Initialize, 
Adjust, and Finalize operations for controlled types, this idiom is 
pretty standard.

In my experience I have never needed access discriminants, but some 
smart people say they are needed for compatibility with other OO languages.