[Oberon] Oberon for a C++ user.

[Andreas Pirklbauer]

Felix,
below is the output (under Experimental Oberon) of a modified set of your modules A, B, and C (source code appended below).

It nicely shows that C.Delete selects the "right" module B, i.e. either the "old B" (here called B*), or the "new B" (here called B). The type descriptors and the code of module B* (removed from module list) is still available in memory.

All type tests automatically select the "right" type descriptor and the "old B" is only removed from memory when no more references from the remaining modules exist.

Andreas

COMMAND SEQUENCE (see below for source code of A, B, and C):
B.Insert 1             ... insert elemt from old BSystem.ShowModules     ... B is the old BSystem.Free B/f        ... remove old B from module list, don't release memorzSystem.ShowModules     ... B* is the old BB.Insert 2             ... new BSystem.ShowModules     ... B* is the old B, B is the new BC.Delete 1             ... deletes the element created by the old BC.Delete 2             ... deletes the element created by the old BC.Init                 ... clears the data structure rooted in A.rootModules.Collect        ... collects B* (no longer referenced)System.ShowModules     ... module B* no longer in memory

GENERATED OUTPUT:
1) B.Insert 1insert element from module B module descriptor at  000212C0
2) System.ShowModulesB        000212C0 000213D0   0A        00020F60 00020FDC   1System   0001CB80 0001D320   0...
3) System.Free B/fB unloading: removing from module list (references exist)
4) System.ShowModules*B       000212C0 000213D0   0 (removed from module list)A        00020F60 00020FDC   1System   0001CB80 0001D320   0...
5) B.Insert 2insert element from module B module descriptor at  00021800
6) System.ShowModulesB        00021800 00021910   0*B       000212C0 000213D0   0 (removed from module list)A        00020F60 00020FDC   2System   0001CB80 0001D320   0...
7) C.Delete 1type of t is T from module B* module descriptor at  000212C0
8) C.Delete 2type of t is T from module B module descriptor at  00021800
9) C.Init + Modules.Collect + System.ShowModulesB        00021800 00021910   0A        00020F60 00020FDC   2System   0001CB80 0001D320   0...
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MODULE A; (*base module managing data structure of base type T*)  TYPE T* = POINTER TO R;    P* = PROCEDURE (t: T);    R* = RECORD i*: INTEGER;      close*: P;      next: T    END ;
  VAR root*: T;
  PROCEDURE Find*(i: INTEGER): T;    VAR t: T;  BEGIN t := root;    WHILE (t # NIL) & (t.i # i) DO t := t.next END ;    RETURN t  END Find;
  PROCEDURE Insert*(t: T);    VAR s: T;  BEGIN s := Find(t.i);    IF s = NIL THEN t.next := root; root := t END  END Insert;
  PROCEDURE Delete*(i: INTEGER);    VAR s, t: T;  BEGIN t := root; s := t;    WHILE (t # NIL) & (t.i # i) DO s := t; t := t.next END ;    IF t # NIL THEN t.close(t);      IF t = root THEN root := NIL ELSE s.next := t.next END    END  END Delete;
  PROCEDURE Init*;  BEGIN root := NIL  END Init;
BEGIN InitEND A.
--------------------------------------
MODULE B; (*client of A, defining extensions of A.T*)  IMPORT A, Modules, Texts, Oberon;  TYPE T* = POINTER TO R;    R* = RECORD (A.R) j: INTEGER END;
  VAR M: Modules.Module;    W: Texts.Writer;
  PROCEDURE Close*(t: A.T);    VAR S: Texts.Scanner;  BEGIN    IF (t IS T) & (M # NIL) THEN      Texts.WriteString(W, "type of t is T from module "); Texts.WriteString(W, M.name);      Texts.WriteString(W, " module descriptor at "); Texts.WriteHex(W, ORD(M));      Texts.WriteLn(W); Texts.Append(Oberon.Log, W.buf)    END  END Close;
  PROCEDURE Insert*;    VAR S: Texts.Scanner; t: T;  BEGIN Texts.OpenScanner(S, Oberon.Par.text, Oberon.Par.pos); Texts.Scan(S);    IF S.class = Texts.Int THEN NEW(t); t.i := S.i; t.close := Close; A.Insert(t);      Texts.WriteString(W, "insert element from module "); Texts.WriteString(W, M.name);      Texts.WriteString(W, " module descriptor at "); Texts.WriteHex(W, ORD(M));      Texts.WriteLn(W); Texts.Append(Oberon.Log, W.buf)    END  END Insert;
  PROCEDURE Init*;  BEGIN  END Init;
BEGIN Texts.OpenWriter(W); M := Modules.root;  WHILE (M # NIL) & (M.name # "B") DO M := M.next ENDEND B.
--------------------------------------

ODULE C; (*tool module*)  IMPORT A, Texts, Oberon;
  VAR W: Texts.Writer;
  PROCEDURE Delete*;    VAR S: Texts.Scanner;  BEGIN Texts.OpenScanner(S, Oberon.Par.text, Oberon.Par.pos); Texts.Scan(S);    IF S.class = Texts.Int THEN A.Delete(S.i) END  END Delete;
  PROCEDURE Init*;  BEGIN  END Init;
BEGIN Texts.OpenWriter(W)END C.
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