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Implement [OsStr]::join #96744

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May 6, 2022
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Implement [OsStr]::join #96744

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17 changes: 17 additions & 0 deletions library/std/src/ffi/os_str.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1222,6 +1222,23 @@ impl OsStr {
}
}

#[unstable(feature = "slice_concat_ext", issue = "27747")]
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The tracking issue #27747 was closed a while ago.

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I used the same tracking issue the other impl blocks for that trait have. The reason to close the tracking issue was because the feature is to be perma-unstable: #27747 (comment) . I'm not sure about changes in policy, but in the older times tracking issues for perma-unstable things would remain open indefinitely.

impl<S: Borrow<OsStr>> alloc::slice::Join<&OsStr> for [S] {
type Output = OsString;

fn join(slice: &Self, sep: &OsStr) -> OsString {
let Some(first) = slice.first() else {
return OsString::new();
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Why not use slice::split_first?

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Didn't know the function existed, thanks! Feel free to file a PR.

Ideally, one would make an optimized implementation like there is for str slices, but OsStr is platform dependent in its representation as well as the invariants, so it's not as easy as just exporting that function from alloc, probably as perma unstable and #[doc(hidden)] and then using it, at least not on unixes. It's a larger project and I wasn't sure if the PR was going to accepted at all, so I went with the simplest implementation I could think of, establishing a baseline that can later be improved. Maybe a good next step would be to use the join_generic_copy function on Unix and fall back on the current implementation on other operating systems, but without benchmarking I don't know how much that is an improvement.

};
let first = first.borrow().to_owned();
slice[1..].iter().fold(first, |mut a, b| {
a.push(sep);
a.push(b.borrow());
a
})
}
}

#[stable(feature = "rust1", since = "1.0.0")]
impl Borrow<OsStr> for OsString {
#[inline]
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14 changes: 14 additions & 0 deletions library/std/src/ffi/os_str/tests.rs
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Expand Up @@ -84,6 +84,20 @@ fn test_os_string_reserve_exact() {
assert!(os_string.capacity() >= 33)
}

#[test]
fn test_os_string_join() {
let strings = [OsStr::new("hello"), OsStr::new("dear"), OsStr::new("world")];
assert_eq!("hello", strings[..1].join(OsStr::new(" ")));
assert_eq!("hello dear world", strings.join(OsStr::new(" ")));
assert_eq!("hellodearworld", strings.join(OsStr::new("")));
assert_eq!("hello.\n dear.\n world", strings.join(OsStr::new(".\n ")));

assert_eq!("dear world", strings[1..].join(&OsString::from(" ")));

let strings_abc = [OsString::from("a"), OsString::from("b"), OsString::from("c")];
assert_eq!("a b c", strings_abc.join(OsStr::new(" ")));
}

#[test]
fn test_os_string_default() {
let os_string: OsString = Default::default();
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2 changes: 2 additions & 0 deletions library/std/src/lib.rs
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Expand Up @@ -241,6 +241,7 @@
#![feature(intra_doc_pointers)]
#![feature(lang_items)]
#![feature(let_chains)]
#![feature(let_else)]
#![feature(linkage)]
#![feature(min_specialization)]
#![feature(must_not_suspend)]
Expand Down Expand Up @@ -300,6 +301,7 @@
#![feature(toowned_clone_into)]
#![feature(try_reserve_kind)]
#![feature(vec_into_raw_parts)]
#![feature(slice_concat_trait)]
//
// Library features (unwind):
#![feature(panic_unwind)]
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