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| author | Tom Levy <tomlevy93@gmail.com> | 2017-08-22 17:10:46 +1200 |
|---|---|---|
| committer | Joe Tsai <thebrokentoaster@gmail.com> | 2017-08-25 20:48:39 +0000 |
| commit | 2bba267120ad8ce7e9ecd97f3ce4b08bce80b41b (patch) | |
| tree | 3bd5bf913274ae453d29e0710f9e74714df4e45b /src/sort | |
| parent | aea286b449c5ffe6d69fb7bb0c5b05e480ed3ad9 (diff) | |
| download | go-2bba267120ad8ce7e9ecd97f3ce4b08bce80b41b.tar.gz go-2bba267120ad8ce7e9ecd97f3ce4b08bce80b41b.zip | |
sort: fix mix-up between "!less" and "greater" in examples
If Less(a, b) returns true when a is less than b, the correct way to
check if a is greater than b is to use Less(b, a). It is wrong to use
!Less(a, b) because that checks if a is greater than *or equal to* b.
1. The decreasingDistance function in Example_sortKeys makes this
mistake. Fix it.
2. The documentation of multiSorter.Less says it loops along the less
functions until it finds a comparison "that is either Less or
!Less". This is nonsense, because (Less(a, b) or !Less(a, b)) is
always true. Fix the documentation to say that it finds a
comparison "that discriminates between the two items (one is less
than the other)". The implementation already does this correctly.
Change-Id: If52b79f68e4fdb0d1095edf29bdecdf154a61b8d
Reviewed-on: https://go-review.googlesource.com/57752
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Diffstat (limited to 'src/sort')
| -rw-r--r-- | src/sort/example_keys_test.go | 2 | ||||
| -rw-r--r-- | src/sort/example_multi_test.go | 9 |
2 files changed, 6 insertions, 5 deletions
diff --git a/src/sort/example_keys_test.go b/src/sort/example_keys_test.go index a8e47e4926..648f919e68 100644 --- a/src/sort/example_keys_test.go +++ b/src/sort/example_keys_test.go @@ -73,7 +73,7 @@ func Example_sortKeys() { return p1.distance < p2.distance } decreasingDistance := func(p1, p2 *Planet) bool { - return !distance(p1, p2) + return distance(p2, p1) } // Sort the planets by the various criteria. diff --git a/src/sort/example_multi_test.go b/src/sort/example_multi_test.go index 40d12152ce..de6ec142d1 100644 --- a/src/sort/example_multi_test.go +++ b/src/sort/example_multi_test.go @@ -49,10 +49,11 @@ func (ms *multiSorter) Swap(i, j int) { } // Less is part of sort.Interface. It is implemented by looping along the -// less functions until it finds a comparison that is either Less or -// !Less. Note that it can call the less functions twice per call. We -// could change the functions to return -1, 0, 1 and reduce the -// number of calls for greater efficiency: an exercise for the reader. +// less functions until it finds a comparison that discriminates between +// the two items (one is less than the other). Note that it can call the +// less functions twice per call. We could change the functions to return +// -1, 0, 1 and reduce the number of calls for greater efficiency: an +// exercise for the reader. func (ms *multiSorter) Less(i, j int) bool { p, q := &ms.changes[i], &ms.changes[j] // Try all but the last comparison. |