on Tue Nov 01 2016, Andrew Trick <swift-users-AT-swift.org> wrote: >> On Nov 1, 2016, at 11:55 AM, Manfred Schubert via swift-users >> <swift-users@swift.org> wrote: >> >> The "UnsafeRawPointer Migration" guide talks about "binding memory >> to a type“ as if that was a well known term. I have never heard of >> it yet though, and googling it returns no relevant results. I do not > >> understand what binding memory is supposed to do. >> >> The migration guide says "Binding uninitialized memory to a type >> prepares the memory to store values of that type“, but clearly raw >> memory does not need to be prepared (and cannot be) to hold any >> arbitrary type and value. >> >> So what is this for, what does it actually do, and to whom is it done (the >> raw pointer, or the > typed pointer which is returned, or the raw memory)? >> >> >> Manfred > > Hi Manfred, > > 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). > It affects the abstract state of the memory location, independent of > the pointer variable used to access that memory. Binding memory > returns a typed pointer for convenience and clarity, but there’s > nothing special about that particular pointer value. > > Initialized memory is always bound to some type. A rawpointer can be > used to access that memory without knowing its bound type. > > -Andy > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users -- -Dave _______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
