-- File:	TDF_AttributeDelta.cdl
--      	----------------------
-- Author:	DAUTRY Philippe
--		<fid@fox.paris1.matra-dtv.fr>
---Copyright:	 MATRA DATAVISION 1997

---Version:	0.0
---History:	Version	Date		Purpose
--		0.0	Sep  8 1997	Creation



deferred class AttributeDelta from TDF inherits TShared from MMgt

	---Purpose: This class discribes the services we need to
	--           implement Delta and Undo/Redo services.
	--           
	--          AttributeDeltas are applied in an unpredictable
	--          order. But by the redefinition of the method
	--          IsNowApplicable, a condition can be verified
	--          before application. If the AttributeDelta is not
	--          yet applicable, it is put at the end of the
	--          AttributeDelta list, to be treated later. If a
	--          dead lock if found on the list, the
	--          AttributeDeltas are forced to be applied in an
	--          unpredictable order.


uses

    Label     from TDF,
    Attribute from TDF
    
is

    Initialize(anAttribute: Attribute from TDF);
    

    Apply(me : mutable)
    	is deferred;
    	---Purpose: Applies the delta to the attribute.
    
    Label(me)
    	returns Label from TDF;
	---Purpose: Returns the label concerned by <me>.

    Attribute(me)
    	returns Attribute from TDF;
	---Purpose: Returns the reference attribute.

    ID(me)
    	returns GUID from Standard;
	---Purpose: Returns the ID of the attribute concerned by <me>.


    ---Category: Miscelleaneous
    --           --------------------------------------------------------------

    Dump(me; OS : in out OStream from Standard)
    	returns OStream from Standard
    	is virtual;
	---Purpose: Dumps the contents.
	--          
	---C++: return &
	---C++: alias operator<<

fields

    myAttribute : Attribute from TDF;
    myLabel     : Label from TDF;

end AttributeDelta;