On Friday 08 November 2013 06:33:23 Niko Matsakis wrote: > I am not sure why Daniel says that a `~str` or `~[]` is not an "owned > box". I guess he's using the term in some specific way. I consider > `~str` and `~[]` to be exactly the same as any other `~T` value in > usage and semantics. They are allocated on the same heap, moved from > place to place, and freed at the same time, etc. > > The difference between a type like `str` or `[T]` and other types is > that `str` and `[T]` are actually a series of values: `u8` bytes and > `T` values respectively. This entails a change in representation and > is also the reason that one *must* use a pointer to refer to them, > because the number of values is not known and hence the compiler can't > calculate the size of the value. > > Note that we are to some extent evolving how we handle dynamically > sized types like `str` and `[]`. Right now they are quite second class > (you can't impl them etc) but that will change. Nonetheless, it will > remain true that you can never have a *value* of type `str` or `[]`, > but most always use a pointer (either `~[]` or `&[]`). > > Also note that a type like `~[T]` is in fact going to be represented > not as a single pointer but rather three pointers, thanks to work by > Daniel in fact.
What's wrong with sticking with convention here? E.g. C++'s `string` and `vector<T>` are objects containing two or three pointers. D's arrays and `string` act the same way. Even C's dynamic arrays (`int x[]`) can be thought of the same way (if one avoids thinking of them as pointers). So why not consider `str` and `[T]` conglomerates of a fixed size containing the pointers (start, length and capacity or whatever) needed? Semantically it's the same while syntactically it's simpler. Slices will need new names of course, but I think the resulting decrease in confusion will be worth it. (D's developers tried to go the other way, with all arrays and slices being effectively copy-on-write slices, before realising that discrete array/slices types _were_ needed.) DH
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