在 2013年11月19日 下午8:35，"spir" <[email protected]>写道：
>
> On 11/19/2013 12:51 PM, Daniel Micay wrote:
>>
>> So in your opinion, what's wrong with the `Boxes` section?
>>
>> http://static.rust-lang.org/doc/master/tutorial.html#boxes
>>
>> I happen to think it does a pretty good job of explaining why `~` is
>> required for recursive types, which is almost the only use case for it
>> from a purely semantic perspective (not worrying about performance).
>
>
> If this is all true, that recursive structures are the main, "almost the
only use case" of ~ pointers, then the tutorial is in my view rather ok on
this point. But then, why does it seem there are ~ pointers in every corner
of Rust code? Including numerous cases in the tutorial itself.
>
+1
> Also, how would we explain and term this meaning? "Indirection" is not
good enough (for we introduce indirections for other reasons, if only to
have variable-size content). I'd say "self-similarity" is the right term
here, and self-explaining (see wikipedia if you are not familiar with the
idea). This is, in fact, the actual idea commonly termed "recursivity" in
programming (wrongly, in my view, but this is yet another terminological
issue). A rule about ~ pointers thus may be:
>
> Whenever one needs self-similarity, use a ~ pointer.
> This lets the language store the element through the kind
> of indirection that permits a self-similar structure.
>
> (I'm not happy of this formulation, neither, still obscure.)
>
> however, other comments on ~ pointers (eg comparisons with C++
unique_ptr, notes that it means owned or "my") introduce ideas rather
different from the one you suggest here, don't they? Say I manually create
a kind of string or "fix-size" array:
>
> struct String {
> n_bytes : uint,
> bytes : ~[u8],
> }
>
> struct Array <Item> {
> n_items : uint,
> items : ~[Item],
> }
>
> Is it wrong here to ~ point to bytes or items? that's what I'd do,
anyway... If it is right, maybe the actual meaning of ~ is something like
"proper content". Whenever a structure actually contains content which is
actually proper to it, or more generally has (pointed) data participating
to its description, then these contents or descriptive data should pointed
with ~: because they belong / are proper to it.
>
> struct ComplexVisualForm {
> shape : ~ Shape,
> style : ~ Style,
> }
>
> This matches my distinction between things and data (properly speaking).
Data, even when pointed (for technological rather than semantic reasons),
still belong to whatever they are part of. Data are never referenced
(properly speaking), it makes no sense. Things instead exist by themselves,
are always ref'ed, never copied (or moved), it makes no sense. If the
reasoning above about ~ pointers is more or less correct (i doubt it is),
then we have in Rust the proper kind of pointer to point to data, properly
speaking, meaning information about things. Now, to reference things from
multiple points of view, we need something else, proper refs or links, and
they cannot be ordinary pointers (especially not GC'ed): we need true refs,
independant from the data (while pointers hold their addresses).
>
> Denis
>
>
> _______________________________________________
> Rust-dev mailing list
> [email protected]
> https://mail.mozilla.org/listinfo/rust-dev
_______________________________________________
Rust-dev mailing list
[email protected]
https://mail.mozilla.org/listinfo/rust-dev
