• Kris (7/7) Mar 24 2004 If I wish to re-shape the interface to a lower-level library, is there a
• Kris (9/16) Mar 25 2004 BTW, 0.81 happily accepts the following declaration:
• Vathix (8/19) Mar 25 2004 You could still cast the Foo object to Bar and access it. If you don't
• J Anderson (12/24) Mar 25 2004 This is a good idea, except you lose polymorphism to some extent. Often...
• Mike Swieton (10/15) Mar 25 2004 Private inheritance is useful because it makes the "is implemented in
• J Anderson (6/14) Mar 25 2004 I complained about a similar issue before (being about to change the

"Kris" <someidiot earthlink.net> writes:

If I wish to re-shape the interface to a lower-level library, is there a
clean way in D to do this? For example, can one inherit a superclass as
private or protected?

Other alternatives include wrapping the superclass via composition, but
that's not always practical or desirable.

Any ideas?

- Kris

"Kris" <someidiot earthlink.net> writes:

BTW, 0.81 happily accepts the following declaration:

class Foo : private Bar
{
}

but it doesn't have any effect on the visibility of Bar. Would be nice if it
did! Comments?

- Kris


"Kris" <someidiot earthlink.net> wrote in message
news:c3thl7$23co$1 digitaldaemon.com...
 If I wish to re-shape the interface to a lower-level library, is there a
 clean way in D to do this? For example, can one inherit a superclass as
 private or protected?

 Other alternatives include wrapping the superclass via composition, but
 that's not always practical or desirable.

 Any ideas?

 - Kris

Vathix <vathix dprogramming.com> writes:

Kris wrote:
 BTW, 0.81 happily accepts the following declaration:
 
 class Foo : private Bar
 {
 }

You could still cast the Foo object to Bar and access it. If you don't 
want Bar accessible, why not make it a private member rather than using 
inheritence? Or if you must use inheritence, you could override the 
members you want private and call assert(0), then call super.member from 
within the class to call Bar's member instead of Foo's.


 
 but it doesn't have any effect on the visibility of Bar. Would be nice if it
 did! Comments?
 
 - Kris
 

-- 
Christopher E. Miller

J Anderson <REMOVEanderson badmama.com.au> writes:

Vathix wrote:

 Kris wrote:

 BTW, 0.81 happily accepts the following declaration:

 class Foo : private Bar
 {
 }


 You could still cast the Foo object to Bar and access it. If you don't 
 want Bar accessible, why not make it a private member rather than 
 using inheritence? 

This is a good idea, except you lose polymorphism to some extent.  Often 
you want to be able to make lower levels visible by polymorphism but 
hide things in the higher levels.  For example events (mouse move ect..) 
should be visible in the low level but not in the high level because you 
only want the even handler calling these.  Allowing the user of the 
higher level class access just makes things more complicated.

 Or if you must use inheritence, you could override the members you 
 want private and call assert(0), then call super.member from within 
 the class to call Bar's member instead of Foo's.

This is not a good idea. Apart from the confusion to the user of the 
class, there is a lot of work involved to do this. And what if more 
methods are added to the base class?  You have to then maintain two classes.

-- 
-Anderson: http://badmama.com.au/~anderson/

Mike Swieton <mike swieton.net> writes:

On Thu, 25 Mar 2004 17:04:32 -0500, Vathix wrote:
 You could still cast the Foo object to Bar and access it. If you don't 
 want Bar accessible, why not make it a private member rather than using 
 inheritence? Or if you must use inheritence, you could override the 
 members you want private and call assert(0), then call super.member from 
 within the class to call Bar's member instead of Foo's.

Private inheritance is useful because it makes the "is implemented in
terms of" relationship explicit. Public inheritance doesn't mean the same
thing ("is-a"), and niether does composition ("has-a").

I think "say what you mean" is a good way to program. You shouldn't always
need to guess ;)

Mike Swieton
__
Human salvation lies in the hands of the creatively maladjusted. 
	- Martin Luther King, Jr.

J Anderson <REMOVEanderson badmama.com.au> writes:

Kris wrote:

BTW, 0.81 happily accepts the following declaration:

class Foo : private Bar
{
}

but it doesn't have any effect on the visibility of Bar. Would be nice if it
did! Comments?

- Kris
  

I complained about a similar issue before (being about to change the 
visibility of individual methods like you can in C++), so I agree.  This 
should be possible.

-- 
-Anderson: http://badmama.com.au/~anderson/