make (a < b < c) illegal?
Andrei Alexandrescu (See Website For Email)
SeeWebsiteForEmail at erdani.org
Wed Feb 7 17:06:07 PST 2007
Walter Bright wrote:
> Right now, in D (as well as C and C++), when you see the expression:
>
> if (a < b < c)
>
> what is your first thought? Mine is that it was written by a newbie who
> didn't realize that (a < b) returns true or false, and that it does NOT
> mean ((a < b) && (b < c)). The odds approach certainty that this is a
> logic error in the code, and even if it was intentional, it raises such
> a red flag that it shouldn't be used anyway.
>
> Andrei has proposed (and I agreed) that this should be done away with in
> the language, i.e. comparison operators should no longer be associative.
> It's a simple change to the grammar. If one really did want to write
> such code, it could be done with parentheses:
>
> if ((a < b) < c)
>
> to get the original behavior. At least, that looks intentional.
>
> I don't think this will break existing code that isn't already broken.
For the record, (clears throat) let me add that I initially suggested to
make them associative with the right meaning, but was shot down. Making
the comparison operators (and that includes != and ==) nonassociative is
the next best thing to do.
Andrei
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