structure function returns -- how?

[Robert Firth]

In article <326 at bms-at.UUCP> stuart at bms-at.UUCP (Stuart D. Gathman) writes:
>*** The real solution ***
>
>(f)	For an assignment, the caller passes a pointer to the object
>	being assigned.  The function does the copy.
>
>P.S. 	This idea is free provided that the user implements it
>on our compilers or else hires me to implement it on their compiler. :-)
>-- 
>Stuart D. Gathman	<..!seismo!dgis!bms-at!stuart>

Sorry.  This fails if the called function accesses the destination
object via another path.  Consider for instance

Z1 : COMPLEX;

Z1 := SWAP_RE_AND_IM(Z1);

with parameter and result object implemented by reference.

The code of the SWAP has

	return COMPLEX'(ARG.IM,ARG.RE);

If the result is assigned piecemeal to the result place,
then Z1.RE will have been overwritten.  This is clearly a
compiler bug, since nearly all languages specify that the
RHS shall be completely evaluated BEFORE the assignment is
performed, and the error arises because the implementation
violates those semantics.