Re: 'IMAGE

[wdl39!mab@ford-wdl1.arpa (Mark A Biggar)]

In article <1714@nic.cerf.net> sss@nic.cerf.net (Marlene M. Eckert) writes:
>Hello.
>Should the following 'image of an uninitialized
>enumeration type raise CONSTRAINT_ERROR?
>In similar situations our compiler has printed all
>blanks, garbage, and even readable garbage.  Of
>course, the answer is probably in the LRM somewhere...
>---------------------------------------------------------
>with Text_IO; use Text_IO;
>procedure Image is
>type Colors is (Red, Green, Blue);
>My_Color : Colors;  -- Not initialized!
>begin
>  Put_Line(Colors'image(My_Color)); -- Legal?
>end Image;

Using an undefined value like that makes your program erronious and it can do 
anything it damn well pleases, i.e., raise CONSTRAINT_ERROR, Crash the CPU,
Erase your hard disk, even as someone put it in comp.std.c in a similar
discussion cause miniture deamons to blow out your nose!

There has been quite a lot of discussion about this in the Ada9X reviewers
group and Ada9x may well contain something that tightens this up to at
least a bounded error (the program is still in error, it is not required that
the error be detected, but the set of allowed actions is finite and
specified by the standard.)

--
Mark Biggar
mab@wdl1.wdl.loral.com