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Add custom nth_back to Skip #60454

Merged
merged 1 commit into from
Jun 20, 2019
Merged

Add custom nth_back to Skip #60454

merged 1 commit into from
Jun 20, 2019

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acrrd
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@acrrd acrrd commented May 1, 2019

Implementation of nth_back for Skip.
Part of #54054

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r? @cramertj

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label May 1, 2019
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cramertj commented May 1, 2019

r? @scottmcm

@rust-highfive rust-highfive assigned scottmcm and unassigned cramertj May 1, 2019
@timvermeulen
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Looks correct to me, though I don't think we want nth_back to skip any of the elements at the front, similar to how next_back doesn't skip any. I think we can call self.iter.nth_back(n) as long as n < self.len(), without having to involve self.n.

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acrrd commented May 2, 2019

Didn't notice that, I changed it

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scottmcm commented May 9, 2019

Look good, thanks!

@bors r+ rollup

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bors commented May 9, 2019

📌 Commit 1edecacf2021a3381f447c949e6dc3018f4b0be4 has been approved by scottmcm

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 9, 2019
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bors commented May 9, 2019

⌛ Testing commit 1edecacf2021a3381f447c949e6dc3018f4b0be4 with merge 8e9bb42c1edf098a01f7a18737f23ad257978854...

if n < self.len() {
self.iter.nth_back(n)
} else {
None

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scottmcm commented May 9, 2019

@bors r-

Good point, @sinkuu; Thanks!

@acrrd Can you add some more tests for bigger n, and maybe some with by_ref to ensure behavior doesn't change here?

@bors bors added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 9, 2019
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kennytm commented May 9, 2019

@bors r- retry

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 9, 2019
@acrrd acrrd force-pushed the issues/54054_skip branch from 1edecac to b118deb Compare May 9, 2019 19:07
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acrrd commented May 9, 2019

@sinkuu thanks!

@scottmcm I added the test for a bigger n and another test that check that nth_back behave as a non skipped iterator. It's not clear to me how to do the tests you meant using by_ref

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I don't think we want nth_back to skip any of the elements at the front, similar to how next_back doesn't skip any

Isn't this still a concern with the current implementation?

@acrrd acrrd force-pushed the issues/54054_skip branch 2 times, most recently from b7fe202 to edd4879 Compare May 27, 2019 20:22
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acrrd commented May 27, 2019

@timvermeulen thanks :)

fn nth_back(&mut self, n: usize) -> Option<I::Item> {
if n < self.len() {
self.iter.nth_back(n)
} else {
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@sinkuu sinkuu May 28, 2019

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In case n >= self.len() && self.len() != 0, additionally you need to do self.iter.nth_back(self.len() - 1); (or whatever that takes self.len()-items from the back) since the underlying iterator could have side effects.

let mut v = vec![];
let mut it = [1, 2, 3, 4, 5]
    .iter()
    .cloned()
    .inspect(|x| v.push(*x))
    .skip(1);
assert_eq!(it.len(), 4);
assert_eq!(it.nth_back(4), None);
assert_eq!(v, vec![5, 4, 3, 2]);

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Why let _ = and not just the call to nth_back?

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@sinkuu sinkuu May 28, 2019

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It was just for expressing intent to throw away the return value of nth_back, and I don't meant it is actually needed.

@@ -2280,6 +2280,32 @@ fn test_skip_try_folds() {
assert_eq!(iter.next_back(), Some(24));
}

#[test]
fn test_skip_nth_back() {
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I don't think the comment above was addressed; if disagree please add a test that demonstrates that the underlying iterator is still advanced.

(You could do that with inspect, or something like let mut it = ...; it.by_ref().skip(10).nth_back(100); assert_eq!(it.next_back(), ...);)

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Ok, I didn't understand you meant that.

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You're now calling self.len() three times, maybe it's better to store it in a variable first.

@acrrd acrrd force-pushed the issues/54054_skip branch 2 times, most recently from 8e83410 to 2966f58 Compare May 29, 2019 20:13
@acrrd acrrd force-pushed the issues/54054_skip branch from 2966f58 to e80a375 Compare May 29, 2019 20:34
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Ping from triage, @acrrd what's the status of this? Are there still open review comments to be addressed, or is this waiting on someone to approve?

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acrrd commented Jun 19, 2019

@jonas-schievink I think all comments are addressed, waiting for approval.

@jonas-schievink jonas-schievink added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jun 19, 2019
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Sorry for the delay re-reviewing, this looks great now!

@bors r+ rollup

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bors commented Jun 20, 2019

📌 Commit e80a375 has been approved by scottmcm

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jun 20, 2019
Centril added a commit to Centril/rust that referenced this pull request Jun 20, 2019
Add custom nth_back to Skip

Implementation of nth_back for Skip.
Part of rust-lang#54054
bors added a commit that referenced this pull request Jun 20, 2019
Rollup of 4 pull requests

Successful merges:

 - #60454 (Add custom nth_back to Skip)
 - #60772 (Implement nth_back for slice::{Iter, IterMut})
 - #61782 (suggest tuple struct syntax)
 - #61968 (rustc: disallow cloning HIR nodes.)

Failed merges:

r? @ghost
@bors bors merged commit e80a375 into rust-lang:master Jun 20, 2019
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9 participants