On Friday, July 27, 2012 04:00:56 Stuart wrote: > On Friday, 27 July 2012 at 00:25:49 UTC, Jonathan M Davis wrote: > > scope on local variables is going to be deprecated, because > > it's unsafe. > > Um...could you explain why? I thought scope on locals was a > really nice feature. I was looking forward to making use of it > for deterministic resource deallocation.
It's inherently unsafe. What happens if you returned a reference to foo from someFunc? Or if you assigned a reference to foo to anything and then tried to use it after someFunc has returned? You get undefined behavior, because foo doesn't exist anymore. If you really need foo to be on the stack, then maybe you should make it a struct. However, if you really do need scope for some reason, then you can use std.typecons.scoped, and it'll do the same thing. scope on local variables is going away for pretty much the same reason that delete is. They're unsafe, and the fact that they're in the core language encourages their use. So, they're being removed and put into the standard library instead. > Besides, if scope(exit) is still allowed, how is that any different? scope(exit) doesn't necessarily have anything to do with deallocating memory. It's far more general than that. It just runs an arbitrary statement when exiting the scope that it's declared in. There's nothing inherently unsafe about that. You _can_ do unsafe operations in it, but you can do that pretty much anywhere. So, if you were to free GC-allocated memory in a scope statement, then you'd be in exactly the same sinking boat that scope puts you in. Freeing GC-allocated memory is inherently unsafe. It's the GC's job to do that. If you really want to be managing memory yourself, then you should be using malloc and free. But for those occasions when you really do end up needing that sort of control with GC memory, we have stuff like std.typecons.scoped and core.memory. They just shouldn't be used under normal circumstances, and you have to be careful with them, so you should only used them when you know what you're doing - which is in stark contrast to having delete and scope in the core language where everyone sees them and thinks that they're perfectly safe to use, completely ignoring or being completely unaware of the dangers involved. We give you the power to blow your foot off if you want to, but we don't want to prime the gun and hand it to you, just make it available if you need it. - Jonathan M Davis
