Thanks Rick, but from .directory upwards the inheritance chain isn't it:

.directory -> .MapCollection -> .Collection

So what about this in section 5.3.19:

If argument is a MapCollection, then index values are used to determine membership, and items are
inserted into the result using the index and item pairs.

Ruurd

On 21-8-2013 0:46, Rick McGuire wrote:
What you are missing is the act of coercing the source collection into a compatible type (this is described in section 5.3.19 The Concept of Set Operations). In this situation, the items are used to integration with the set. If you wish to merge the indexes, then source~allindexes as an argument for the merge.

Rick


On Tue, Aug 20, 2013 at 5:19 PM, Ruurd Idenburg <ru...@idenburg.net <mailto:ru...@idenburg.net>> wrote:

    This is the description of set~intersection:

    5.3.14.4. intersection
    >>-intersection(argument)--------------------------------------><
    Returns a new collection (of the same class as the receiver)
    containing only those items from the receiver
    whoseindexes are in both the receiver collection and the argument
    collection. The argument can be any
    collection class object. The argument must also allow all of the
    index values in the receiver collection.

    and I think this is the code for set~intersection in CoreClasses.orx:

    ::METHOD intersection                  -- take the intersection of
    sets
    use strict arg other                   -- get the companion object
    signal on nomethod
    new = self~class~new                   -- use a new instance
    if other~isA(.Collection) then
    values = other~allitems -- get all of the items from the other
    collection
    else
        values = other~makearray           -- ask for an array version
    of the source
    count = values~items
    do i = 1 to count
        index = values[i]
        -- if we have one of these, put into the result
        -- NB:  Since this is a SET, there will only be one copy
    accumulated.
        if self~hasindex(index) then
             new~put(index)
    end
    return new                             -- return the difference
    collection
    nomethod:                              -- unknown method sent
      raise syntax 93.948 array(1, "Collection")

    In my case the other collection is a .directory, where items and
    indexes are not necessarily the same.

    What am I misunderstanding?

    -- Ruurd Idenburg

    
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Ruurd Idenburg

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