Killing integer division problems?

burt invalid_email_address at
Tue Aug 4 12:34:37 UTC 2020


A while ago I spent an hour figuring out why some variable wasn't 
changing like it should, and the reason was something like the 
following (although in a much more complex expression):

double y = 0.0;
// ...
y += 1 / b; // with b : int
// ...

I have run into this C remnant multiple times now and spent much 
too long trying to find out what happened, so to fix it, here's 
my proposal:

"Make integer division without cast illegal."

In the case above, the compiler would complain (or at least emit 
a warning) that there is integer division going on and that the 
result will be truncated.

If I want to keep the integer division behaviour, I would just 
have to change the code to:

y += cast(int) (1 / b);

If I don't want to keep that behaviour, then the compiler has 
shown me the bug and I can fix it:

y += 1.0 / b;

It doesn't silently change behaviour that used to be valid in C 
(it will emit a warning) and can be fixed trivially, so it 
shouldn't be an intrusive change (and might even catch bugs that 
weren't found yet).

Would such a change require a DIP? Could a -preview/-transition 
flag be added to warn me about integer divisions? What do you 

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