Re: Reprise: 'in out' parameters for functions

[Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de>]

Wojtek Narczynski <wojtek@power.com.pl> wrote:
: Hello,
: 
:> I take it Ada forces abstraction in version in cases?
:> Could you name an example unit to look at?
: 
: 'Inversion' not 'in version' incase it were more than a typo.

A typo, sorry.

: When you
: implement a semaphore over a protected object, or in general when you
: need to lock / unlock by yourself. Classic example:
: 
: polyorb-tasking-profiles-full_tasking-mutexes.adb

Thanks. Given that mutex and semaphores have been known
when Ada was made, I wonder whether there aren't some
external forces at work which lead to the requirement
of using tasking constructs below language level.
Not Ada's fault from this perspective.

Incidentally, there is some abstraction inversion criticism
quoting Ada, mutex, and tasks. But has not been brought up
to date where date refers to 1995. So there is another
meaning of "classic".

 
: function in_kilograms (x: Quantity) return Units.yard;
: -- Blows at runtime

I don't think so. How do you write an expression expecting
Unis.kilogram, where the compiler sees a function returning
Units.yard, such that the compiler does not reject?

: This just cannot be done right in Ada.


:> What's missing?
: 
: From the language? For example parameters for exceptions.

Not a good idea I think, though practical for use in quick and
dirty fixes of design errors. Programm logic can be programmed.