RE: List container strawman 1.2

["Steven Deller" <deller@smsail.com>]

> -----Original Message-----
> From: comp.lang.ada-admin@ada.eu.org 
> [mailto:comp.lang.ada-admin@ada.eu.org] On Behalf Of Marin 
> David Condic ]
> Sent: Monday, November 12, 2001 10:33 AM
> To: comp.lang.ada@ada.eu.org
> Subject: Re: List container strawman 1.2
> 
> 
> Lots of ways of handling that. I agree that there are cases 
> where you want a list to contain only one sample of a given 
> element, but I'd prefer that the instantiation doesn't force 
> someone to make that decision and have to provide parameters 
> that may be unnecessary for the simple cases. It could just 
> as easily be done by providing a subprogram to set a flag in 
> the List object that disallows/allows duplicates. Or 
> alternately, returning a flag on insertion indicating there 
> was a duplicate or providing a function to test for a 
> duplicate, or .... ? IOW, default behavior is "duplicates 
> allowed" unless you call "Disallow_Duplicates 
> (My_List_Object) ;" or something similar.

In many "interesting" cases, duplicates are only defined over a subset
of the information in an element.  The approach suggested does not have
sufficient power to handle anything except "simple" duplication.  If
could also provide a generic "=" for the elements then perhaps it is
useful.

Also, these lists are NOT sorted, so non-duplication would require
searching the entire list for each insertion. As I said in previous
email, it is not good to have O(N) performance for primitive operations
on primitive structures.

Non-duplication insertion is better left to implementations intended for
sorted lists.  In which case, I'd expect "insert based on key" to be one
of the primitive operations.  And the user would NOT have the ability to
specify where in a list an insertion was going to be done.

Regards,
Steve