[Gambas-user] Feature request: Giving _compare() an optional user data argument

[B Bruen]

On Wed, 14 May 2014 21:38:33 +0200
Tobias Boege <taboege at ...626...> wrote:

> Hi Benoit,
> 
> when we wanted to sort a 2d array (table) by a specific column, variable at
> runtime, we did the following:
> 
>  1. Create the class, let's call it "Record", to represent the table
>     records which implements a _compare() method and has a SortField
>     property which indicates to _compare() which column we want to sort
>     by.
>  2. Create a class "RecordGroup" which Inherits Object[] and has a
>     SortField(Field As Integer, Optional Mode As Integer) method which is
>     a multicolumn-aware version of Sort:
> 
>     Public Sub SortField(Field As Integer, Optional Mode As Integer)
>       Dim iInd As Integer
> 
>       For iInd = 0 To Super.Count - 1
>         Super[iInd].SortField = Field
>       Next
>       Super.Sort(Mode)
>     End
>  3. Then, we must work with RecordGroups which we can sort by, say, column 7
>     using myGroup.SortField(7).
> 
> You see that we need to set each object's SortField property to the Field
> value in order to make the _compare()s work together as we desire. If some
> objects "don't get it", we will lose transitivity of our relation and the
> sort may fail.
> 
> We can't use static properties in the Record class either because we may
> want to have multiple groups.
> 
> These redundant assignments are what bothers us (also that we need a custom
> array type that we called "Group" to hide our clumsiness in communicating
> the SortField to each object). [ There are other ways of efficiently grouping
> elements but the ones I can think of are pretty obscure - but I'm open for
> suggestions! If none: ]
> 
> Is it possible to - and what will existing code say if we - change
> _compare()'s signature to
> 
>   Public Sub _compare(hOther As Object, Optional vPrivate As Variant)
> 
> and have a new corresponding optional argument to Object[].Sort() and
> MyClass[].Sort()? Sorting by column 7 in the above scenario would boil
> down to calling (without groups) Record[].Sort(7).
> 
> Regards,
> Tobi
> 

I would really like to see this too! My attempts at providing a generic sorting mechanism along the lines suggested by Tobi's approach have been less than successful for exactly the same reasons.

-- 
B Bruen <bbruen at ...2308...>