Add generic conversion traits #23538

aturon · 2015-03-20T00:17:23Z

This commit:

Introduces std::convert, providing an implementation of
RFC 529.
Deprecates the AsPath, AsOsStr, and IntoBytes traits, all
in favor of the corresponding generic conversion traits.

Consequently, various IO APIs now take As<Path> rather than
AsPath, and so on. Since the types provided by std implement both
traits, this should cause relatively little breakage.
Deprecates many from_foo constructors in favor of from.
Changes PathBuf::new to take no argument (creating an empty buffer,
as per convention). The previous behavior is now available as
PathBuf::from.
De-stabilizes IntoCow. It's not clear whether we need this separate trait.

Closes #14433
Closes #22751

[breaking-change]

r? @alexcrichton
cc @gankro @erickt @cmr

aturon · 2015-03-20T00:17:44Z

PRELIMINARY PR: Do not merge until the RFC is approved.

aturon · 2015-03-20T00:19:27Z

cc @sfackler @wycats

aturon · 2015-03-20T00:26:10Z

Per IRC: @alexcrichton is very uncomfortable with these living in libcollections rather than libcore. This placement was to facilitate impls like impl<T: Clone> To<Vec<T>> for [T] which would otherwise be disallowed due to coherence.

aturon · 2015-03-20T00:26:39Z

cc @reem

aturon · 2015-03-20T00:30:37Z

Per IRC: @reem points out that the same coherence problems make it much more difficult to define "implicit conversions" via generics targetting user-land types: you cannot implement To<MyType<T>> for StdType<T> due to coherence.

Introducing an ad hoc conversion trait, on the other hand, makes it possible to do this in userland.

aturon · 2015-03-20T00:52:56Z

Updated: I've now moved the traits into libcore, and have a (rather sad) impl of To<Vec<u8>> for [u8] which coherence permits.

bors · 2015-03-20T09:51:49Z

☔ The latest upstream changes (presumably #23548) made this pull request unmergeable. Please resolve the merge conflicts.

aturon · 2015-03-20T16:41:54Z

I believe this is now ready to go, once the RFC itself has been merged.

alexcrichton · 2015-03-20T17:17:28Z

src/libcollections/borrow.rs

@@ -14,6 +14,7 @@

 use core::clone::Clone;
 use core::cmp::{Eq, Ord, Ordering, PartialEq, PartialOrd};
+use core::convert::As;


Could these traits also go into the libcore prelude? I think files like this can have use core::prelude::* at the top as well (slowly been migrating over time).

alexcrichton · 2015-03-20T21:27:57Z

cc #23567

aturon · 2015-03-23T21:51:20Z

Updated:

Removed To for the time being.
Renamed As to AsRef.
Renamed all methods to match their trait names.
All conversion functionality now in libcore; added to core::prelude
Added From => Into implementation, which makes it possible to add conversions in both directions without running afoul of coherence. For example, we now have From<[T]> for Vec<T> where T: Clone, which yields the corresponding Into going in the other direction -- despite the fact that the two types live in different crates.

I also believe this addresses a few concerns about things implementing From instead of Into
Removed AsRef impls for slices from Option/Result, which was causing a bad interaction with their as_ref methods. This functionality is available by calling as_slice directly.

All in all, I feel much better with the form this PR is taking now. It feels cleaner, leaner, more consistent and more extensible. Thanks for the feedback making this possible!

@alexcrichton: re-r?

alexcrichton · 2015-03-23T21:57:24Z

src/libstd/env.rs

@@ -67,8 +67,8 @@ pub fn current_dir() -> io::Result<PathBuf> {
 /// println!("Successfully changed working directory to {}!", root.display());
 /// ```
 #[stable(feature = "env", since = "1.0.0")]
-pub fn set_current_dir<P: AsPath + ?Sized>(p: &P) -> io::Result<()> {
-    os_imp::chdir(p.as_path())
+pub fn set_current_dir<P: AsRef<path::Path> + ?Sized>(p: &P) -> io::Result<()> {


Could this module import Path directly and use AsRef<Path>?

Ahha! It can now. I think when I first wrote it Path was still in the prelude :)

alexcrichton · 2015-03-23T21:59:30Z

I, too, am quite happy with how this is turning out! r=me with the as_slice methods on Option and Result remaining #[unstable] (as they were before)

aturon · 2015-03-23T22:00:25Z

pings addressed :)

alexcrichton · 2015-03-23T22:02:29Z

@bors: r+ 8389253

aturon · 2015-03-23T22:12:16Z

@bors: r=alexcrichton 97c8e43

Conflicts: src/librustc_back/rpath.rs

This commit: * Introduces `std::convert`, providing an implementation of RFC 529. * Deprecates the `AsPath`, `AsOsStr`, and `IntoBytes` traits, all in favor of the corresponding generic conversion traits. Consequently, various IO APIs now take `AsRef<Path>` rather than `AsPath`, and so on. Since the types provided by `std` implement both traits, this should cause relatively little breakage. * Deprecates many `from_foo` constructors in favor of `from`. * Changes `PathBuf::new` to take no argument (creating an empty buffer, as per convention). The previous behavior is now available as `PathBuf::from`. * De-stabilizes `IntoCow`. It's not clear whether we need this separate trait. Closes rust-lang#22751 Closes rust-lang#14433 [breaking-change]

alexcrichton · 2015-03-24T21:02:41Z

Rolled into #23654

bors · 2015-03-24T21:05:53Z

☔ The latest upstream changes (presumably #23654) made this pull request unmergeable. Please resolve the merge conflicts.

rust-highfive assigned alexcrichton Mar 20, 2015

aturon force-pushed the conversion branch from 9fcd79f to 844c115 Compare March 20, 2015 00:52

aturon mentioned this pull request Mar 20, 2015

RFC: Generic conversion traits rust-lang/rfcs#529

Merged

aturon force-pushed the conversion branch 6 times, most recently from c8671be to 3c62067 Compare March 20, 2015 06:52

alexcrichton reviewed Mar 20, 2015
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aturon force-pushed the conversion branch from 3c62067 to dbd9480 Compare March 23, 2015 21:47

aturon changed the title ~~[WIP] Add generic conversion traits~~ Add generic conversion traits Mar 23, 2015

alexcrichton reviewed Mar 23, 2015
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aturon force-pushed the conversion branch from dbd9480 to a686d27 Compare March 23, 2015 21:59

aturon force-pushed the conversion branch from a686d27 to 8389253 Compare March 23, 2015 22:01

aturon force-pushed the conversion branch from 8389253 to 97c8e43 Compare March 23, 2015 22:11

alexcrichton added a commit to alexcrichton/rust that referenced this pull request Mar 23, 2015

rollup merge of rust-lang#23538: aturon/conversion

fd13400

Conflicts: src/librustc_back/rpath.rs

aturon force-pushed the conversion branch from 97c8e43 to 08ee682 Compare March 23, 2015 23:38

alexcrichton closed this Mar 24, 2015

SimonSapin mentioned this pull request Mar 25, 2015

Implement generic conversion traits #23567

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Add generic conversion traits #23538

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