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From: wojtek@power.com.pl (Wojtek Narczynski)
Newsgroups: comp.lang.ada
Subject: Re: Reprise: 'in out' parameters for functions
Date: 9 Apr 2004 19:28:52 -0700
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Date: 2004-04-09T19:28:52-07:00
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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. 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

Or try to implement tree crabbing. Hell, try to implement a list
updateable concurrently from multiple tasks. You _will_ end up
implementing a semaphore over a protected, over a semaphore.

Or the simplest possible: two protected counters, try to get the sum
atomically.

> : type system unable
> : to express physical units,
> 
> Still, you might have
> 
>    type Quantity is abstract tagged private;
> 
>    function in_meters (x: Quantity) return Units.meter;
>    function in_yards (x: Quantity) return Units.yard;
>    --  etc...

Sure, let us continue:

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

This just cannot be done right in Ada.

> : But the problem real problem IMO is that
> : the development of the language has stagnated.
> 
> What's missing?

>From the language? For example parameters for exceptions.

Regards,
Wojtek