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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:23:18 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-16 19:23:18 +0000 |
commit | 43a123c1ae6613b3efeed291fa552ecd909d3acf (patch) | |
tree | fd92518b7024bc74031f78a1cf9e454b65e73665 /src/sort/example_keys_test.go | |
parent | Initial commit. (diff) | |
download | golang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.tar.xz golang-1.20-43a123c1ae6613b3efeed291fa552ecd909d3acf.zip |
Adding upstream version 1.20.14.upstream/1.20.14upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'src/sort/example_keys_test.go')
-rw-r--r-- | src/sort/example_keys_test.go | 96 |
1 files changed, 96 insertions, 0 deletions
diff --git a/src/sort/example_keys_test.go b/src/sort/example_keys_test.go new file mode 100644 index 0000000..648f919 --- /dev/null +++ b/src/sort/example_keys_test.go @@ -0,0 +1,96 @@ +// Copyright 2013 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package sort_test + +import ( + "fmt" + "sort" +) + +// A couple of type definitions to make the units clear. +type earthMass float64 +type au float64 + +// A Planet defines the properties of a solar system object. +type Planet struct { + name string + mass earthMass + distance au +} + +// By is the type of a "less" function that defines the ordering of its Planet arguments. +type By func(p1, p2 *Planet) bool + +// Sort is a method on the function type, By, that sorts the argument slice according to the function. +func (by By) Sort(planets []Planet) { + ps := &planetSorter{ + planets: planets, + by: by, // The Sort method's receiver is the function (closure) that defines the sort order. + } + sort.Sort(ps) +} + +// planetSorter joins a By function and a slice of Planets to be sorted. +type planetSorter struct { + planets []Planet + by func(p1, p2 *Planet) bool // Closure used in the Less method. +} + +// Len is part of sort.Interface. +func (s *planetSorter) Len() int { + return len(s.planets) +} + +// Swap is part of sort.Interface. +func (s *planetSorter) Swap(i, j int) { + s.planets[i], s.planets[j] = s.planets[j], s.planets[i] +} + +// Less is part of sort.Interface. It is implemented by calling the "by" closure in the sorter. +func (s *planetSorter) Less(i, j int) bool { + return s.by(&s.planets[i], &s.planets[j]) +} + +var planets = []Planet{ + {"Mercury", 0.055, 0.4}, + {"Venus", 0.815, 0.7}, + {"Earth", 1.0, 1.0}, + {"Mars", 0.107, 1.5}, +} + +// ExampleSortKeys demonstrates a technique for sorting a struct type using programmable sort criteria. +func Example_sortKeys() { + // Closures that order the Planet structure. + name := func(p1, p2 *Planet) bool { + return p1.name < p2.name + } + mass := func(p1, p2 *Planet) bool { + return p1.mass < p2.mass + } + distance := func(p1, p2 *Planet) bool { + return p1.distance < p2.distance + } + decreasingDistance := func(p1, p2 *Planet) bool { + return distance(p2, p1) + } + + // Sort the planets by the various criteria. + By(name).Sort(planets) + fmt.Println("By name:", planets) + + By(mass).Sort(planets) + fmt.Println("By mass:", planets) + + By(distance).Sort(planets) + fmt.Println("By distance:", planets) + + By(decreasingDistance).Sort(planets) + fmt.Println("By decreasing distance:", planets) + + // Output: By name: [{Earth 1 1} {Mars 0.107 1.5} {Mercury 0.055 0.4} {Venus 0.815 0.7}] + // By mass: [{Mercury 0.055 0.4} {Mars 0.107 1.5} {Venus 0.815 0.7} {Earth 1 1}] + // By distance: [{Mercury 0.055 0.4} {Venus 0.815 0.7} {Earth 1 1} {Mars 0.107 1.5}] + // By decreasing distance: [{Mars 0.107 1.5} {Earth 1 1} {Venus 0.815 0.7} {Mercury 0.055 0.4}] +} |