add AsRef<[u8]> for both str and String

[seanmonstar]

r? @aturon

[alexcrichton]

Does this compile when rebased on #25120? It makes the meaning of vec_of_strings.concat() ambiguous as it could return Vec<Vec<u8>> or a String

[seanmonstar]

Ah carps, you're right, that does make it ambiguous. Possibilities:

1. Scrap this idea. However, it feels right to be able to make APIs generic over bytes AsRef<[u8]>, and including strings would be an ergo win.
2. Require vec_of_strings.concat() be explicit.
3. Change the implementations of SliceConcatExt to 4 implementations, 1 for each [T], Vec<T>, str, and String, instead of relying on AsRef<U>.

[alexcrichton]

After some discussion with @aturon he has convinced me that we definitely want the ability to add these AsRef implementations, and we can touch up SliceConcatExt for now by using Borrow as the bound on those generic impl blocks instead of AsRef (as str will never implement Borrow<[u8]> due to hashing differences).

That will be a breaking change but is likely to have very little fallout, so we'll probably include it for beta. Could you update this PR with that change?

[seanmonstar]

@alexcrichton updated, passes make check-stage1.

[alexcrichton]

@bors: r+ 8e491ef p=50

Thanks @seanmonstar!

[bors]

⌛ Testing commit 8e491ef with merge c033d98...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-32-nopt-t, auto-win-32-opt, auto-win-64-nopt-t, auto-win-64-opt

[bluss]

Dabo on irc says something broke with .connect()

< Dabo> This used to work, but doesn't anymore with the latest nightly: 
              some_set.iter().collect::<Vec<_>>().connect(", ")
< Dabo> `type `collections::vec::Vec<&collections::string::String>` does not implement any 
              method in scope named `connect``
< Dabo> I have rustc 1.1.0-nightly (dc630d01e 2015-05-09) (built 2015-05-10)

[daboross]

Full code example that breaks: http://is.gd/vdlpTma

This isn't a major use-case I wouldn't think, but just noting an example of that here.

[seanmonstar]

I forgot to include [breaking-change] in the last commit to :(

[alexcrichton]

Adding beta-accepted as this has been merged into beta