on Wed Nov 02 2016, Andrew Trick <atrick-AT-apple.com> wrote: >> On Nov 2, 2016, at 12:58 PM, Dave Abrahams via swift-users >> <swift-users@swift.org> wrote: >> >>> At the top of the migration guide is a link to the memory model explanation: >>> > https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md#memory-model-explanation >>> > >>> "A memory location's bound type is an abstract, dynamic property of the >>> memory used to formalize >>> type safety.” >>> >>> I’m not sure I like the “prepares the memory” language myself. Binding >>> memory communicates to the compiler that the memory locations are safe >>> for typed access. Nothing happens at runtime--until someone writes a >>> type safety sanitizer. >> >> Well, that's a slight overstatement IMO. Sanitizers aside, the main >> reason for these binding operations is that if you leave them out, >> something different *will* happen at runtime... something that will make >> your code do the wrong thing. >> >> What I would say is that binding the memory has no immediate runtime >> cost... but it's absolutely required if you want your program to behave >> (and sometimes behaving correctly is a little slower than misbehaving). > > Good clarification. I really did not mean to imply that binding memory > to a type has no effect on runtime behavior. Taken out of context, > “nothing happens at runtime” is quite an understatement. > > The original poster seemed to have the impression that the operation > of binding memory itself might affect program state,
Formally speaking, it does! > independent of any compiler optimization. I want to make it clear that > a call to bindMemory(to:capacity:) has no observable runtime side > effects at the point of the call. Only because you can't observe what memory is bound to. > But I need to throw in an exemption for future sanitizers. I don't think you do; sanitizer actions are allowed under undefined behavior. -- -Dave _______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
