docs(slice): Clarification in binary_search_by #46870

ffflorian · 2017-12-20T09:08:52Z

This PR ~~fixes a small comment typo~~ adds some clarification to a half-open interval in the binary_search_by function in slice.

rust-highfive · 2017-12-20T09:08:58Z

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @withoutboats (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

Please see the contribution instructions for more information.

hanna-kruppe · 2017-12-20T10:10:53Z

Thanks for the PR!

However, I don't think this is a typo. [a, b) denotes a half-open interval (>= a and < b) as opposed to a closed interval [a, b] (>= a and <= b), and mid < size is exactly what is needed for this code to work correctly. But perhaps we could clarify the comment a bit to make this clearer for people who haven't seen that notation before?

ffflorian · 2017-12-20T10:11:52Z

@rkruppe
Oh, I understand. Yes, I can add some clarification. Thanks!

hanna-kruppe · 2017-12-20T10:11:34Z

src/libcore/slice/mod.rs

@@ -400,14 +400,14 @@ impl<T> SliceExt for [T] {
        while size > 1 {
            let half = size / 2;
            let mid = base + half;
-            // mid is always in [0, size).
+            // mid is always in [0, size].


Maybe a connective here, e.g., "mid is always in [0, size), i.e., [bullet points below]"

hanna-kruppe · 2017-12-20T10:12:10Z

src/libcore/slice/mod.rs

            // mid >= 0: by definition
            // mid < size: mid = size / 2 + size / 4 + size / 8 ...
            let cmp = f(unsafe { s.get_unchecked(mid) });
            base = if cmp == Greater { base } else { mid };
            size -= half;
        }
-        // base is always in [0, size) because base <= mid.
+        // base is always in [0, size] because base <= mid.


... and here maybe spell out base < size?

What do you mean by that?

Was just thinking about how to make this line more explicit, too. But if you don't see the need to change it, that's fine by me too.

ffflorian · 2017-12-20T10:20:25Z

@rkruppe
Sorry, your change requests appeared only after I pushed my latest commit.

hanna-kruppe

Changes look basically good. However, I'm afraid I'll have to ask you to squash the commits into one -- generally the project prefers to not have unfinished and "undo this" commits, but rather one commit per finished logical step.

Since you're touching the commits anyway, you might want to consider the subjective style issue below.

hanna-kruppe · 2017-12-20T10:20:08Z

src/libcore/slice/mod.rs

@@ -400,14 +400,15 @@ impl<T> SliceExt for [T] {
        while size > 1 {
            let half = size / 2;
            let mid = base + half;
-            // mid is always in [0, size].
+            // mid is always in [0, size).
+            // (that means mid is >= 0 and < size)


Very minor style nit, but since the lines below are effectively subordinate bullet points, I think it would look nicer if this was one line. Fix if you want, or don't.

hanna-kruppe · 2017-12-20T10:24:48Z

No worries! I guess I should have bundled them together with my first comment. What you wrote independently is good too, these were just suggestions.

ffflorian · 2017-12-20T10:30:53Z

@rkruppe
I implemented your suggested changes and squashed my commits into one. 🙂

hanna-kruppe · 2017-12-20T10:34:57Z

src/libcore/slice/mod.rs

            // mid >= 0: by definition
            // mid < size: mid = size / 2 + size / 4 + size / 8 ...
            let cmp = f(unsafe { s.get_unchecked(mid) });
            base = if cmp == Greater { base } else { mid };
            size -= half;
        }
-        // base is always in [0, size) because base <= mid.
+        // base is always in [0, size) because base <= mid and base < size.


Hm, as written that isn't exactly clarifying. Let's just drop it — you're the one who was confused by this and evidently you didn't see the need to clarify this line.

Drop the PR or this line?

This line. The other change is great :)

hanna-kruppe · 2017-12-20T10:45:02Z

Great. Thanks again for taking the time, and sorry for all the back and forth ❤️

@bors r+

bors · 2017-12-20T10:45:03Z

📌 Commit f6ab79d has been approved by rkruppe

ffflorian · 2017-12-20T10:46:11Z

@rkruppe

sorry for all the back and forth

No worries, thanks for taking your time! 🙂

docs(slice): Clarification in binary_search_by This PR ~fixes a small comment typo~ adds some clarification to a half-open interval in the `binary_search_by` function in `slice`.

Rollup of 14 pull requests - Successful merges: #46359, #46517, #46671, #46751, #46760, #46787, #46794, #46828, #46831, #46835, #46851, #46852, #46856, #46870 - Failed merges:

rust-highfive assigned withoutboats Dec 20, 2017

hanna-kruppe suggested changes Dec 20, 2017

View reviewed changes

ffflorian changed the title ~~fix(slice): Typo in binary_search_by~~ fix(slice): Clarification in binary_search_by Dec 20, 2017

hanna-kruppe suggested changes Dec 20, 2017

View reviewed changes

ffflorian changed the title ~~fix(slice): Clarification in binary_search_by~~ docs(slice): Clarification in binary_search_by Dec 20, 2017

hanna-kruppe reviewed Dec 20, 2017

View reviewed changes

docs(slice): Clarify half-open interval

f6ab79d

kennytm mentioned this pull request Dec 20, 2017

Rollup of 14 pull requests #46874

Merged

kennytm added the S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. label Dec 20, 2017

bors merged commit f6ab79d into rust-lang:master Dec 20, 2017

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docs(slice): Clarification in binary_search_by #46870

docs(slice): Clarification in binary_search_by #46870

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docs(slice): Clarification in binary_search_by #46870

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