Re: Run-time accessibility checks

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 11 Dec 2008 12:21:34 +0100, Georg Bauhaus wrote:

> Dmitry A. Kazakov schrieb:
> 
>> This is what I call abstract record interface. For each component it will
>> have two operations:
>> 
>>    function ".<component>" (R : Abstract_Record_Type)
>>       return Component_Type is abstract;
>>    procedure ".<component>"
>>       (R : in out Abstract_Record_Type; C : Component_Type) is abstract;
>> 
>> The compiler uses the second (setter) for all LHS X.Component.
> 
> That with pre/post/invariant constraints, in case the
> component setting procedure has access to the object
> containing the component.

It is a primitive operation of the abstract record type, but not of the
component. If you wanted to have it a primitive operation of both, you
would have to support MD, which is I don't know how to do (properly).

> Could pre/post/invariant also help when checking order of
> component assignments?

Which order? A record type does not declare any specific access order for
its components. If you have record aggregates in mind that is another
interface and another issue. Aggregate is a form of a constructor with some
special syntax.

> (These are called "assigner commands" in Eiffel.)

There are pretty clear rules about what happens with pre/post/invariant
upon inheritance (Liskov). The only problem is that many people (like Meyer
and possibly you) honestly believe they could make pre/post/invariant
dynamic. Count me out.

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