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# Source file src/sort/example_interface_test.go

## Documentation: sort

```     1  // Copyright 2011 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
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  }
59
```

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