1 // Copyright 2012 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 rand_test 6 7 import ( 8 "fmt" 9 "math/rand" 10 "os" 11 "text/tabwriter" 12 ) 13 14 // These tests serve as an example but also make sure we don't change 15 // the output of the random number generator when given a fixed seed. 16 17 func Example() { 18 rand.Seed(42) // Try changing this number! 19 answers := []string{ 20 "It is certain", 21 "It is decidedly so", 22 "Without a doubt", 23 "Yes definitely", 24 "You may rely on it", 25 "As I see it yes", 26 "Most likely", 27 "Outlook good", 28 "Yes", 29 "Signs point to yes", 30 "Reply hazy try again", 31 "Ask again later", 32 "Better not tell you now", 33 "Cannot predict now", 34 "Concentrate and ask again", 35 "Don't count on it", 36 "My reply is no", 37 "My sources say no", 38 "Outlook not so good", 39 "Very doubtful", 40 } 41 fmt.Println("Magic 8-Ball says:", answers[rand.Intn(len(answers))]) 42 // Output: Magic 8-Ball says: As I see it yes 43 } 44 45 // This example shows the use of each of the methods on a *Rand. 46 // The use of the global functions is the same, without the receiver. 47 func Example_rand() { 48 // Create and seed the generator. 49 // Typically a non-fixed seed should be used, such as time.Now().UnixNano(). 50 // Using a fixed seed will produce the same output on every run. 51 r := rand.New(rand.NewSource(99)) 52 53 // The tabwriter here helps us generate aligned output. 54 w := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', 0) 55 defer w.Flush() 56 show := func(name string, v1, v2, v3 interface{}) { 57 fmt.Fprintf(w, "%s\t%v\t%v\t%v\n", name, v1, v2, v3) 58 } 59 60 // Float32 and Float64 values are in [0, 1). 61 show("Float32", r.Float32(), r.Float32(), r.Float32()) 62 show("Float64", r.Float64(), r.Float64(), r.Float64()) 63 64 // ExpFloat64 values have an average of 1 but decay exponentially. 65 show("ExpFloat64", r.ExpFloat64(), r.ExpFloat64(), r.ExpFloat64()) 66 67 // NormFloat64 values have an average of 0 and a standard deviation of 1. 68 show("NormFloat64", r.NormFloat64(), r.NormFloat64(), r.NormFloat64()) 69 70 // Int31, Int63, and Uint32 generate values of the given width. 71 // The Int method (not shown) is like either Int31 or Int63 72 // depending on the size of 'int'. 73 show("Int31", r.Int31(), r.Int31(), r.Int31()) 74 show("Int63", r.Int63(), r.Int63(), r.Int63()) 75 show("Uint32", r.Uint32(), r.Uint32(), r.Uint32()) 76 77 // Intn, Int31n, and Int63n limit their output to be < n. 78 // They do so more carefully than using r.Int()%n. 79 show("Intn(10)", r.Intn(10), r.Intn(10), r.Intn(10)) 80 show("Int31n(10)", r.Int31n(10), r.Int31n(10), r.Int31n(10)) 81 show("Int63n(10)", r.Int63n(10), r.Int63n(10), r.Int63n(10)) 82 83 // Perm generates a random permutation of the numbers [0, n). 84 show("Perm", r.Perm(5), r.Perm(5), r.Perm(5)) 85 // Output: 86 // Float32 0.2635776 0.6358173 0.6718283 87 // Float64 0.628605430454327 0.4504798828572669 0.9562755949377957 88 // ExpFloat64 0.3362240648200941 1.4256072328483647 0.24354758816173044 89 // NormFloat64 0.17233959114940064 1.577014951434847 0.04259129641113857 90 // Int31 1501292890 1486668269 182840835 91 // Int63 3546343826724305832 5724354148158589552 5239846799706671610 92 // Uint32 2760229429 296659907 1922395059 93 // Intn(10) 1 2 5 94 // Int31n(10) 4 7 8 95 // Int63n(10) 7 6 3 96 // Perm [1 4 2 3 0] [4 2 1 3 0] [1 2 4 0 3] 97 } 98 99 func ExamplePerm() { 100 for _, value := range rand.Perm(3) { 101 fmt.Println(value) 102 } 103 104 // Unordered output: 1 105 // 2 106 // 0 107 } 108
