HasSortKeys

CompareItems CompareItemsBySortKey SecondarySortKeys

Attributes

ReverseOrder SortKey

Fields

Define Class HasSortKeys;
    mixes in with ObjectList, SortedList;
    
    attribute SortKey: OperationNumber, safe, noGetter, noSetter;
        // a numeric key used to determine the primary criteria CompareItems should use;
        // must override getter to return the numeric key;
        // must override setter to store the numeric key somewhere, typically in a field of overriding subclass
    attribute ReverseOrder: Boolean, noGetter, noSetter;
        // determines whether the list should be sorted in reverse of normal order;
        // reverse order is only used for primary sort key;
        // must override getter to return the current value;
        // must override setter to store the new value, typically in a field of overriding subclass
        
    overrides CompareItems;
        // returns result of CompareItemsBySortKey on sort key, if result is non-zero;
        // otherwise calls CompareItemsBySortKey repeatedly on each SecondarySortKey 
        // that is not the primary sort key until items are distinguished;
        // if primary sort key is zero, returns zero immediately;
        // override rarely (override CompareItemsBySortKey instead)
    operation CompareItemsBySortKey(index1: Unsigned; index2: Unsigned;
            element1: Object; element2: Object;
            sortKey: OperationNumber): SignedShort, noMethod;
        // called repeatedly by CompareItems to determine sort order;
        // returns -1 to sort element1 before element2 when sorting by sortKey;
        // returns 1 to sort element1 after element2 when sorting by sortKey;
        // returns 0 when element1 and element2 are not distinguished when sorting by sortKey
        // must override to handle all sortKeys that subclass should handle
    operation SecondarySortKeys(keyList: OperationNumberList);
        // called by CompareItems to obtain ordered list of sort keys to use if
        // two items are not distinguished when sorting by primary sort key;
        // override to add secondary sort keys to keyList;
        // if not overridden, only primary sort key will be used by CompareItems;
        // since the sorting is non-destructive, not supplying secondary keys allows
        // the user to control the overall order by multiple sorts.
        // CompareItems will ignore primary sort key if it is included in list 
end class;