m3tk/src/gast/AST_CopyRep.i3


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 Copyright (C) 1993, Digital Equipment Corporation           
 All rights reserved.                                        
 See the file COPYRIGHT for a full description.              

INTERFACE AST_CopyRep;
This is not intended as a client interface, but as support for the implementation of a tree copy interface. ASTCopy is one such interface. All AST nodes must provide an implementation of the copy method.

IMPORT AST, AST_WalkRep;

TYPE
  NODE = AST_WalkRep.NODE OBJECT
    METHODS
      copy(handle: Handle): AST.NODE RAISES ANY := Null;
    END;

REVEAL AST.NODE <: NODE;

TYPE
  Handle <: Handle_public;
  Handle_public = OBJECT
    METHODS
      Copy(n: AST.NODE): AST.NODE RAISES ANY;
  END;

PROCEDURE Null(n: NODE; handle: Handle): AST.NODE RAISES {};
returns NIL; used as the default method

END AST_CopyRep.
The copy method returns a copy of some part of the tree rooted at the node making the call. At this level of abstraction copy is very loosely defined. Precisely which attributes are copied, and whether attributes are {\em shallow-copied} or {\em deep-copied} is left to specific AST interfaces to define.

To aid in the creation of flexible copying interfaces, the copy method takes a Handle argument, in a similar style to the walk method defined in AST_WalkRep. Each implementation of the copy method should create a new instance of itself and then apply handle.Copy to each of its children in turn, children, assigning the results to the corresponding child attributes of the new instance.