On 13/12/13 20:29, Liigo Zhuang wrote:
looks like a good idea.
I always think "extern mod extra" is repetitious, because, when i "use
extra::Something", the compiler always know I'm using the mod "extra".
You only need one `extern mod extra` per program which is hardly
repetitive, and, what if you have a submodule called `extra`, how can
the compiler tell that you want to be importing from it, rather than the
extra crate?
(In general, one has to explicitly import external crates, because they
can be named anything.)
Huon
2013/12/13 Piotr Kukiełka <[email protected]
<mailto:[email protected]>>
Hi all,
I'm new to rust but I'm quite interested in learning it more
deeply and contributing to language itself.
However right now I'm just studying tutorial/manual/wiki to
understand it better, and sometimes I have doubts about language
design.
My biggest concern so far was connected with module system.
Right now rust have 3 different (if I'm counting correctly)
keywords used for marking which library/module should be imported
and used.
Why not just one? It would actually solve few problems at once.
So, this is my idea:
Drop *mod* and *extern mod *keywords and just leave *use*.
Since there would be only one keyword responsible for importing
left, you wouldn't need to care about their order.
Then, when compiler see new identifiers it checks:
1) If there is local definition of it available? If there is, then
we are done.
2) Is there matching import in scope?
a) If yes, then is it labeled with resource path marker?
*) If yes, then check if it's:
+) Path to local file => it's equivalent of
#[path=".."] modrust;
+) Something like
"http://github.com/mozilla/rust"; => it's equivalent of
externmodrust= "github.com/mozilla/rust
<http://github.com/mozilla/rust>";
+) Something like "rust:0.8" => it's equivalent
of externmodmy_rust(name= "rust", vers= "0.8"); *) If
no, then first check local mods, and if nothing is found then scan
libs (extern mod)
b) If no, then it's unknown symbol and we got error
What are the real benefits?
1) End user just need to remember and understand one syntax, *use,
*examples:
usefarm;
usemy_farm(path= "farm", vers= "2.5");
usemy_farm(path= "http://github.com/farming/farm";, vers= "2.5");
usemy_farm(path= "../../farm/farm.rs <http://farm.rs>");
2) You don't need 3 special keywords
3) Order of use doesn't matter (and there are no doubts about
shadowing order).
4) You don't need special cases usesuper anduse self,you can use
path to replace them as well (i.e. to replace self:
usesome_child_module::some_item(path= ".");)
5) You won't link unused modules even if they are imported with *use.*
6) If I'll decide to move part of my modules to separate library
it can still work without code changes
7) It would be easy to implement imports which works only in scope
this way (as it is done in scala for example)
8) this way use works more like import on jvm than include in
C/C++ (and I think C style include should be avoided)
Downsides?
I probably don't know all corner cases and maybe there are good
and valid reasons to do it as it done right now.
But unless they are really good then I think simplification of
imports should be seriously considered.
Best regards,
Piotr Kukielka
*
*
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by *Liigo*, http://blog.csdn.net/liigo/
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