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 // Copyright 2011 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" ) type Person struct { Name string Age int } func (p Person) String() string { return fmt.Sprintf("%s: %d", p.Name, p.Age) } // ByAge implements sort.Interface for []Person based on // the Age field. type ByAge []Person func (a ByAge) Len() int { return len(a) } func (a ByAge) Swap(i, j int) { a[i], a[j] = a[j], a[i] } func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age } func Example() { people := []Person{ {"Bob", 31}, {"John", 42}, {"Michael", 17}, {"Jenny", 26}, } fmt.Println(people) // There are two ways to sort a slice. First, one can define // a set of methods for the slice type, as with ByAge, and // call sort.Sort. In this first example we use that technique. sort.Sort(ByAge(people)) fmt.Println(people) // The other way is to use sort.Slice with a custom Less // function, which can be provided as a closure. In this // case no methods are needed. (And if they exist, they // are ignored.) Here we re-sort in reverse order: compare // the closure with ByAge.Less. sort.Slice(people, func(i, j int) bool { return people[i].Age > people[j].Age }) fmt.Println(people) // Output: // [Bob: 31 John: 42 Michael: 17 Jenny: 26] // [Michael: 17 Jenny: 26 Bob: 31 John: 42] // [John: 42 Bob: 31 Jenny: 26 Michael: 17] }