> On Mar 30, 2016, at 3:11 AM, Jeremy Pereira via swift-evolution > <swift-evolution@swift.org> wrote: >> On 25 Mar 2016, at 23:00, Brent Royal-Gordon via swift-evolution >> <swift-evolution@swift.org> wrote: >> >>> In the low level world, there is no such thing as an invalid address; both >>> 0x0 and ~0x0 are perfectly valid byte pointers. So using something else >>> than 0x0 for Swift invalid pointer just shuffle the problem around. >> >> Let me state it this way: You cannot write a fully-conforming C compiler for >> a platform which does not have some way to represent an invalid pointer. > > This is not true. > > In both C99 and C11, the result of dereferencing an invalid pointer (of which > the null pointer is one example) is undefined behaviour. This means it is > perfectly fine for the null pointer to be represented by a bit pattern that > is also a valid address and for the compiler not to bother generating a check > that the pointer is not null.
This is not correct. Two pointers are not permitted to compare equal when one operand is a null pointer and the other is a pointer to an object. John. > >> However C does it, Swift can do the same thing. > > C does it by sweeping the problem under the carpet of undefined behaviour. > >> >> -- >> Brent Royal-Gordon >> Architechies >> >> _______________________________________________ >> swift-evolution mailing list >> swift-evolution@swift.org >> https://lists.swift.org/mailman/listinfo/swift-evolution > > _______________________________________________ > swift-evolution mailing list > swift-evolution@swift.org > https://lists.swift.org/mailman/listinfo/swift-evolution _______________________________________________ swift-evolution mailing list swift-evolution@swift.org https://lists.swift.org/mailman/listinfo/swift-evolution
