-- File:	SelectDeduct.cdl
-- Created:	Tue Nov 17 19:13:08 1992
-- Author:	Christian CAILLET
--		<cky@topsn2>
---Copyright:	 Matra Datavision 1992


deferred class SelectDeduct  from IFSelect  inherits Selection

    ---Purpose : A SelectDeduct determines a list of Entities from an Input
    --           Selection, by a computation : Output list is not obliged to be
    --           a sub-list of Input list
    --           (for more specific, see SelectExtract for filtered sub-lists,
    --            and SelectExplore for recurcive exploration)
    --            
    --           A SelectDeduct may use an alternate input for one shot
    --           This allows to use an already existing definition, by
    --           overloading the input selection by an alternate list,
    --           already defined, for one use :
    --           If this alternate list is set, InputResult queries it instead
    --           of calling the input selection, then clears it immediately

uses AsciiString from TCollection, EntityIterator, Graph,
     SelectionIterator, SelectPointed

raises InterfaceError

is

    SetInput (me : mutable; sel : mutable Selection);
    ---Purpose : Defines or Changes the Input Selection

    Input (me) returns mutable Selection;
    ---Purpose : Returns the Input Selection

    HasInput (me) returns Boolean;
    ---Purpose : Returns True if the Input Selection is defined, False else

    HasAlternate (me) returns Boolean;
    ---Purpose : Tells if an Alternate List has been set, i.e. : the Alternate
    --           Definition is present and set

    Alternate (me : mutable) returns SelectPointed;
    ---Purpose : Returns the Alternate Definition
    --           It is returned modifiable, hence an already defined
    --           SelectPointed can be used
    --           But if it was not yet defined, it is created the first time
    --           
    --           It is exploited by InputResult
    ---C++ : return &

    InputResult (me; G : Graph) returns EntityIterator;
    ---Purpose : Returns the Result determined by Input Selection, as Unique
    --           if Input Selection is not defined, returns an empty list.
    --           
    --           If Alternate is set, InputResult takes its definition instead
    --           of calling the Input Selection, then clears it

    -- RootResult remains to be defined by each class of Selection


    FillIterator (me; iter : in out SelectionIterator);
    ---Purpose : Puts in an Iterator the Selections from which "me" depends
    --           This list contains one Selection : the InputSelection

fields

    thesel : Selection;
    thealt : SelectPointed;

end SelectDeduct;