Re: How to get nice with GNAT?

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

On Tue, 25 Nov 2014 05:45:45 -0800 (PST), brbarkstrom@gmail.com declaimed
the following:


>2) An exception is raised without an exception handler in the called procedure:
>the exception is propagated back to the caller.  I believe a pass-by-copy
>parameter that is an "out" parameter in the interface propagates out to the
>caller with the last assigned value.
>

	<SNIP>

>These behaviors are consistent with what I've observed in the execution of the
>compiled versions of the code I provided in previous posts.  I think the only
>question about whether different compilers would implement this behavior is
>item 2), although I have not been able to find a clear statement in RM as
>to whether not passing back a pass-by-copy value is left to the implementer
>in the event of the exception being raised.

	Have to dig up some ancient history...

http://archive.adaic.com/standards/83rat/html/ratl-08-02.html#8.2.3
"""
If the execution of a subprogram is abandoned as the result of an exception
not handled locally, then the final value of an actual parameter that is
associated with a formal parameter of mode in out may depend on the
parameter passing mechanism: If by copy, the final value will still be the
initial value before the call.
"""

Does leave OUT only parameters hanging, unless one just takes the view that
IN OUT and OUT both rely upon copying from procedure local memory to return
parameter memory at the same point (and an IN OUT copies from the parameter
memory to local memory upon entry).

"""
The allowed mechanisms follow from the above considerations.

	a.	For scalar types, and for all modes, all parameter passing must be
achieved by copy. The same treatment applies to access types, for the
reasons given in the previous section. 

	b.	For record and array types, the language does not specify whether
parameter passing is achieved by reference or by copy. ...
"""
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/