Add core::iter::once_with() #57579

ghost · 2019-01-13T16:43:35Z

Functions iter::once() and iter::repeat() construct iterators from values. The latter has the lazy variant iter::repeat_with(), but the former doesn't. This PR therefore adds iter::once_with().

Another way to think of iter::once_with() is that it's a function that converts FnOnce() -> T into Iterator<Item = T>.

If this seems like a reasonable addition, I'll open a tracking issue and update the #[feature(...)] attributes.

frewsxcv · 2019-01-13T17:50:16Z

cc @rust-lang/libs

Centril · 2019-01-13T18:14:38Z

r? @SimonSapin

I once promised @eddyb to make a PR for this but the playground ate my work... :(
Thank you for writing this up!

SimonSapin · 2019-01-14T16:07:46Z

r=me, but the doc-comment still needs #![feature(iter_once_with)]

SimonSapin · 2019-01-14T16:22:45Z

src/libcore/iter/sources.rs

+/// over each file of the `.foo` directory, but also a configuration file,
+/// `.foorc`:
+///
+/// ```no_run


I’d guess here too? IIRC no_run doc-tests are still compiled.

SimonSapin · 2019-01-14T20:07:58Z

@bors r+

bors · 2019-01-14T20:08:00Z

📌 Commit 3a1f013 has been approved by SimonSapin

Add core::iter::once_with() Functions `iter::once()` and `iter::repeat()` construct iterators from values. The latter has the lazy variant `iter::repeat_with()`, but the former doesn't. This PR therefore adds `iter::once_with()`. Another way to think of `iter::once_with()` is that it's a function that converts `FnOnce() -> T` into `Iterator<Item = T>`. If this seems like a reasonable addition, I'll open a tracking issue and update the `#[feature(...)]` attributes.

@ghost

Rollup of 7 pull requests Successful merges: - #57253 (Make privacy checking, intrinsic checking and liveness checking incremental) - #57352 (forbid manually impl'ing one of an object type's marker traits) - #57537 (Small perf improvement for fmt) - #57579 (Add core::iter::once_with()) - #57587 (Add 'rustc-env:RUST_BACKTRACE=0' to const-pat-ice test) - #57608 (Simplify 'product' factorial example) - #57614 ([rustdoc] Fix crates filtering box not being filled) Failed merges: r? @ghost

Add core::iter::once_with() Functions `iter::once()` and `iter::repeat()` construct iterators from values. The latter has the lazy variant `iter::repeat_with()`, but the former doesn't. This PR therefore adds `iter::once_with()`. Another way to think of `iter::once_with()` is that it's a function that converts `FnOnce() -> T` into `Iterator<Item = T>`. If this seems like a reasonable addition, I'll open a tracking issue and update the `#[feature(...)]` attributes.

@ghost

Rollup of 8 pull requests Successful merges: - #56044 (Drop partially bound function parameters in the expected order) - #57352 (forbid manually impl'ing one of an object type's marker traits) - #57456 (RawVec doesn't always abort on allocation errors) - #57467 (Implement `check_attribute` to forbid `#[allow_internal_unsafe]`) - #57579 (Add core::iter::once_with()) - #57587 (Add 'rustc-env:RUST_BACKTRACE=0' to const-pat-ice test) - #57608 (Simplify 'product' factorial example) - #57614 ([rustdoc] Fix crates filtering box not being filled) Failed merges: r? @ghost

kumbayo · 2019-01-15T18:50:58Z

src/libcore/iter/sources.rs

@@ -377,6 +377,119 @@ pub fn once<T>(value: T) -> Once<T> {
    Once { inner: Some(value).into_iter() }
 }

+/// An iterator that repeats elements of type `A` endlessly by
+/// applying the provided closure `F: FnMut() -> A`.
+///


It seems like his comment was copy pasted from RepeatWith.
It talks about endless repeating and FnMut().

@kumbayo could you file a PR to fix this?

Add core::iter::once_with

04c74f4

rust-highfive assigned kennytm Jan 13, 2019