On Wed, Jul 20, 2011 at 23:53, Richard O'Keefe <o...@cs.otago.ac.nz> wrote:
> On 21/07/2011, at 9:08 AM, Paul Johnson wrote: > > I would have thought that the compiler, as a matter of optimisation, > could insert a check to see if (==) is comparing an object with itself. The > only way I can see this breaking is with perverse instances of Eq that would > return False for "f == f". > > Presumably inside the body of f, x and x would be > identical pointers, but the only right answer is False, > not True. > > If you think this is a bit far fetched, > consider the IEEE definition of equality for > floating-point numbers: > > let x = 0.0/0.0 in x == x > > The answer is False, so the optimisation breaks down even > with a system-defined type. Also, NaNs are never equal to each other. Also consider SQL's NULL (relevant if you use Takusen, I suspect). -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms
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