Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!math.fu-berlin.de!uniol!unido!infbs!tubsibr!buschman
From: buschman@tubsibr.uucp (Andreas Buschmann)
Newsgroups: comp.lang.modula3
Subject: DISPOSE statement  and other pointer related question
Keywords: DISPOSE LOCATION
Message-ID: <1991Apr10.152310.28913@tubsibr.uucp>
Date: 10 Apr 91 15:23:10 GMT
Sender: buschman@tubsibr.uucp (Andreas Buschmann)
Organization: TU Braunschweig, Informatik (Bueltenweg), Germany
Lines: 57


Hallo,
In the Modula3 report Page 49:

  A DISPOSE Statement has the form:

	DISPOSE (v)

  where v is a writable designator with a fixed or object reference
  type. 
  If v is untraced, the statement frees the storage for v's referent
  and sets v to NIL.  
  Freeing storage to which active references remain is an unchecked
  runtime error.  							(a)
  If v is traced, the statement is equivalent to v := NIL. 
  If v is NIL, the statement is a no-op. 				(b)

Two questions rise here:
  a) is this an unchecked runtime error if and only if v is untraced,
     or is it one if v is traced, too?
  b) is this if and only if v is tracedm or if it is untraced, too?


As I'm writing an interpreter for a subset of Modula3, the answer is
at least interesting for the memory management.

Ah, some additional questions:
  -  is (a) the reason for DISPOSE beeing an unsafe operation?

  -  is there a version of the repost in ascii, or dvi format to
     filter through dvi2tty, to get a report I can grep in?

  -  I have't found a save way (without using unsafe features) getting
     a checked reference onto a variable, or on a part of a structure
     or array. I wan't the same effect as in ALGOL68 writing:

	INT ii := 20;
	REF INT iii := ii;
	write (iii)

     which doesn't make much at the first glance, but is necessary for
     some iterative rewritings of recursive algorithms for linked list
     inserting.
     For my interpreter I created a procedureal operator LOCATION:

	LOCATION (VAR x: Any) : REF Any

     How is this supposed to go in the new standard?

     I am not so happy with th long name LOCATION, but dont want to
     use the abbeviation LOC because of its different meaning in
     Algol68 as a local storage allocator in contrast to HEAP, which
     is semantically equivalent to NEW in m3.

						Tschuess
							Andreas