On 01/15/13 00:07, Timon Gehr wrote: > 'scope' is supposed to restrict escaping references, but it is not entirely > clear what that means, and how to make it powerful enough. Eg. what if part > of a structure can be freely escaped, such as the contents of an array of > Objects, but not the array itself? I'd argue that indirections in parameters > should not be covered by 'scope', because it is not something that is > transitive. (the opposite would be)
A non-transitive scope would not be very useful. Eg. a 'scope' arg could never refer to a stack object - which is the main advantage of having 'scope'. Introducing a second kind of top-level-scope would probably complicate the language too much. > Furthermore, there is the issue of how to treat 'ref' parameters. Different problem - lifetime. One approach would be to disallow escaping them (which in this case includes returning them) unless the compiler is able to do the right - ie the body of the function is available. Somewhat unorthodox, but could work. (The problem are not the trivial cases; it's the ones where the compiler has no idea which ref is escaped/returned at runtime) artur
