Implement Vec::splice and String::splice #32355

SimonSapin · 2016-03-19T14:18:09Z

RFC: rust-lang/rfcs#1432, tracking issue: #32310

rust-highfive · 2016-03-19T14:18:25Z

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SimonSapin · 2016-03-19T14:24:48Z

src/libcollections/vec.rs

+            }
+
+            // There may be more elements. Use the lower bound as an estimate.
+            // FIXME: Is the upper bound a better guess? Or something else?


I’d like some other opinions here. Getting this guess wrong either way causes the tail to be moved twice.

If we over-estimate (which it the moment only happens if size_hint is incorrect) we reserve more space than necessary in the vector. But that space can still be used later (with further calls to Vec::push and friends). Vec::reserve often over-allocates anyway.

If we under-estimate, we allocate a temporary vector and soon drop it.

Maybe over-estimating is better, and this should use the upper bound when it’s Some? (And fall back to the lower bound otherwise.)

Maybe if the optimistic route is only used if Some(lower) == upper, i.e the iterator claims to know its exact size?

If Some(lower) == upper we already use that. If they’re accurate the Vec we then collect is zero-length. The question is what to do when the two bounds are not equal?

bluss · 2016-03-19T18:12:31Z

src/libcollections/vec.rs

+            // There may be more elements. Use the lower bound as an estimate.
+            // FIXME: Is the upper bound a better guess? Or something else?
+            let (lower_bound, _upper_bound) = self.replace_with.size_hint();
+            if lower_bound > 0  {


This condition lower_bound > 0 could be replaced by lower_bound > 0 && Some(lower_bound) == _upper_bound. Just to clarify what I mean.

Ok, I see. In that case we’d avoid moving "tail" elements twice, but we’d allocate a temporary Vec in more cases.

SimonSapin · 2016-03-19T19:51:40Z

It may also make sense to rewrite drain to be based on splice (and std::iter::empty) rather than the reverse. In that case, could Drain be a pub type Drain<'a, T> = Splice<'a, Empty<T>> type alias or would it have to be a wrapper struct?

apasel422 · 2016-03-19T21:21:23Z

src/libcollections/string.rs

@@ -1301,6 +1301,63 @@ impl String {
        }
    }

+    /// Create a splicing iterator that removes the specified range in the string,


s/Create/Creates/

All three fixed, thanks.

SimonSapin · 2016-03-27T18:29:13Z

While we’re talking API (#32355 (comment)), should the replace_with argument of String::splice be I: Iterator<Item=char> rather than &str?

alexcrichton · 2016-03-28T21:29:52Z

Hm for consistency it seems like you may want that but on the other hand it seems like most of the time you'd want to splice in another slice. It's also arguably less performant as splicing a slice would require decoding and re-encoding utf-8, although perhaps we could recover the performance through specialization?

This may be a good question to have open for stabilization (and the tracking issue), but doesn't necessarily seem like an immediately blocker for landing the PR.

SimonSapin · 2016-03-29T12:48:30Z

There is indeed the UTF-8 round-trip overhead, and also the accuracy loss of size_hint. The lower bound of str:Chars::size_hint is utf8_len / 4.

alexcrichton · 2016-03-29T17:14:50Z

Hm the loss of size_hint may be killer for now, perhaps &str can be favored?

SimonSapin · 2016-03-30T05:55:19Z

I’m fine with sticking to &str.

bors · 2016-04-12T14:17:33Z

☔ The latest upstream changes (presumably #32804) made this pull request unmergeable. Please resolve the merge conflicts.

alexcrichton · 2016-05-08T18:28:40Z

ping @SimonSapin, any update on this?

SimonSapin · 2016-05-09T12:34:53Z

I still need to write more tests and haven’t taken the time to do it yet. If someone wants to do so before I do, feel free.

alexcrichton · 2016-05-21T00:25:19Z

Ok, in that case I'm gonna close this out of inactivity, but feel free to reopen/resubmit once the tests are there!

solson · 2017-02-04T16:21:42Z

@alexcrichton Is there some way we can advertise this to see if someone wants to work on it? I hate to see merged RFCs go unimplemented for so long.

alexcrichton · 2017-02-04T19:30:54Z

@solson an interesting idea! @rust-lang/libs, thoughts?

glaebhoerl · 2017-02-05T12:09:00Z

There is (or used to be?) a "help wanted" section in TWiR...

aturon · 2017-02-06T20:57:23Z

I added a comment to the tracking issue and marked it "help wanted", which (I think?) will lead it to TWiR (@brson?).

We ultimately should do something more persistent and general, maybe on the roadmap tracker.

@SimonSapin

Implement Vec::splice and String::splice (RFC 1432) RFC: rust-lang/rfcs#1432, tracking issue: rust-lang#32310 A rebase of rust-lang#32355 with a few more tests. Let me know if you have any ideas for more tests. cc @SimonSapin

@SimonSapin

Implement Vec::splice and String::splice (RFC 1432) RFC: rust-lang/rfcs#1432, tracking issue: rust-lang#32310 A rebase of rust-lang#32355 with a few more tests. Let me know if you have any ideas for more tests. cc @SimonSapin

@SimonSapin

Implement Vec::splice and String::splice (RFC 1432) RFC: rust-lang/rfcs#1432, tracking issue: rust-lang#32310 A rebase of rust-lang#32355 with a few more tests. Let me know if you have any ideas for more tests. cc @SimonSapin

@SimonSapin

Implement Vec::splice and String::splice (RFC 1432) RFC: rust-lang/rfcs#1432, tracking issue: rust-lang#32310 A rebase of rust-lang#32355 with a few more tests. Let me know if you have any ideas for more tests. cc @SimonSapin

@SimonSapin

Implement Vec::splice and String::splice (RFC 1432) RFC: rust-lang/rfcs#1432, tracking issue: #32310 A rebase of #32355 with a few more tests. Let me know if you have any ideas for more tests. cc @SimonSapin

rust-highfive assigned alexcrichton Mar 19, 2016

SimonSapin reviewed Mar 19, 2016
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SimonSapin force-pushed the splice branch from a94d1bb to b589685 Compare March 19, 2016 14:27

bluss reviewed Mar 19, 2016
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SimonSapin force-pushed the splice branch from b589685 to 42266fb Compare March 19, 2016 19:49

apasel422 reviewed Mar 19, 2016
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Add Vec::splice and String::splice

887f35f

SimonSapin force-pushed the splice branch from b11df41 to 887f35f Compare March 25, 2016 08:18

alexcrichton closed this May 21, 2016

alexcrichton mentioned this pull request Jul 12, 2016

Add method String::insert_str #34771

Merged

SimonSapin mentioned this pull request Aug 20, 2016

Implement insert_many<IntoIterator> for SmallVec servo/rust-smallvec#28

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aturon mentioned this pull request Feb 6, 2017

Tracking issue for {Vec,String}::splice #32310

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mattico mentioned this pull request Mar 11, 2017

Implement Vec::splice and String::splice (RFC 1432) #40434

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Implement Vec::splice and String::splice #32355

Implement Vec::splice and String::splice #32355

SimonSapin commented Mar 19, 2016

rust-highfive commented Mar 19, 2016

SimonSapin Mar 19, 2016

bluss Mar 19, 2016

SimonSapin Mar 19, 2016

bluss Mar 19, 2016

SimonSapin Mar 19, 2016

SimonSapin commented Mar 19, 2016

apasel422 Mar 19, 2016

SimonSapin Mar 19, 2016

SimonSapin commented Mar 27, 2016

alexcrichton commented Mar 28, 2016

SimonSapin commented Mar 29, 2016

alexcrichton commented Mar 29, 2016

SimonSapin commented Mar 30, 2016

bors commented Apr 12, 2016

alexcrichton commented May 8, 2016

SimonSapin commented May 9, 2016

alexcrichton commented May 21, 2016

solson commented Feb 4, 2017

alexcrichton commented Feb 4, 2017

glaebhoerl commented Feb 5, 2017

aturon commented Feb 6, 2017

Implement Vec::splice and String::splice #32355

Implement Vec::splice and String::splice #32355

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