On Mar 16, 2006, at 05:09, Robert Dewar wrote:
Not quite right. If you have an uninitialized variable, the value is
invalid and may be out of bounds, but this is a bounded error
situation,
not an erroneous program. So the possible effects are definitely NOT
unbounded, and the use of such values cannot turn a program erroneous.
(that's an Ada 95 change, this used to be erroneous in Ada 83).
Actually, that's a good point and raises some potential issues:
if we're never establish the invariant that a value of a type is in
range, we can only use the base range for variables that might be
used uninitialized. Any read of such a variable would then involve
a range check.
package Uninitialized is
N : Positive;
end Uninitialized;
with Uninitialized;
procedure Test is
for J in 1 .. Uninitialized.N loop
...
end loop;
end Test;
In this case, GCC might replace the loop with
declare
J : Integer := 1;
begin
while J /= Uninitialized.N loop
...
J := J + 1;
end loop;
end;
which would be incorrect for N = 0.
-Geert
