Re: [IDEA+RFC] Possible solution for min()/max() war

[VDA]

Monday, September 03, 2001, 11:35:52 PM, David desJardins
<[e-mail]> wrote:

Dd> The explicit typing of MIN and MAX will avoid some bugs that have to do
Dd> with the comparison of entities of different types.  The explicit typing
Dd> will also introduce some bugs, when a user uses the wrong type (e.g.,
Dd> when the code is initially written with the correct type, but then
Dd> someone later changes the type of the variables, and doesn't remember to
Dd> change the type in the macro call).  Overall, I think it will be about a
Dd> wash.
...
Dd> I think the best approach to bug avoidance would be two-argument MIN and
Dd> MAX functions which require that both arguments have the same type, but
Dd> where that can be any type.  Then users who want to compare objects of
Dd> different types would have to explicitly cast one to the type of the
Dd> other (or both to a third common type).  In the most common case where
Dd> users are simply comparing objects of the same type, there would be no
Dd> need or reason to change the code.

This sounds right!

#define min2(a,b)      ...  <-- checks for a,b being the same type
#define min3(type,a,b) ...  <-- casts a,b to type first

min3(long long,a,b) will be a favorite in bug chasing :-)

Dd> It's simple enough for an external checker to confirm that this rule is
Dd> followed.  The same checker could enforce the same rule for "<" and
Dd> other comparison operators, which would probably help eliminate several
Dd> bugs (without the unacceptably clunky LESSTHAN macro).

Good candidate for Stanford checker, but there will be lots of false
positives.
-- 
Best regards,
VDA
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