libgo/go/sort/example_interface_test.go

   1 // Copyright 2011 The Go Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style
   3 // license that can be found in the LICENSE file.
   4
   5 package sort_test
   6
   7 import (
   8         "fmt"
   9         "sort"
  10 )
  11
  12 type Person struct {
  13         Name string
  14         Age  int
  15 }
  16
  17 func (p Person) String() string {
  18         return fmt.Sprintf("%s: %d", p.Name, p.Age)
  19 }
  20
  21 // ByAge implements sort.Interface for []Person based on
  22 // the Age field.
  23 type ByAge []Person
  24
  25 func (a ByAge) Len() int           { return len(a) }
  26 func (a ByAge) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
  27 func (a ByAge) Less(i, j int) bool { return a[i].Age < a[j].Age }
  28
  29 func Example() {
  30         people := []Person{
  31                 {"Bob", 31},
  32                 {"John", 42},
  33                 {"Michael", 17},
  34                 {"Jenny", 26},
  35         }
  36
  37         fmt.Println(people)
  38         // There are two ways to sort a slice. First, one can define
  39         // a set of methods for the slice type, as with ByAge, and
  40         // call sort.Sort. In this first example we use that technique.
  41         sort.Sort(ByAge(people))
  42         fmt.Println(people)
  43
  44         // The other way is to use sort.Slice with a custom Less
  45         // function, which can be provided as a closure. In this
  46         // case no methods are needed. (And if they exist, they
  47         // are ignored.) Here we re-sort in reverse order: compare
  48         // the closure with ByAge.Less.
  49         sort.Slice(people, func(i, j int) bool {
  50                 return people[i].Age > people[j].Age
  51         })
  52         fmt.Println(people)
  53
  54         // Output:
  55         // [Bob: 31 John: 42 Michael: 17 Jenny: 26]
  56         // [Michael: 17 Jenny: 26 Bob: 31 John: 42]
  57         // [John: 42 Bob: 31 Jenny: 26 Michael: 17]
  58 }