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  }
    59
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