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
5package rand_test
6
7import (
8	"fmt"
9	"math/rand/v2"
10	"os"
11	"strings"
12	"text/tabwriter"
13	"time"
14)
15
16// These tests serve as an example but also make sure we don't change
17// the output of the random number generator when given a fixed seed.
18
19func Example() {
20	answers := []string{
21		"It is certain",
22		"It is decidedly so",
23		"Without a doubt",
24		"Yes definitely",
25		"You may rely on it",
26		"As I see it yes",
27		"Most likely",
28		"Outlook good",
29		"Yes",
30		"Signs point to yes",
31		"Reply hazy try again",
32		"Ask again later",
33		"Better not tell you now",
34		"Cannot predict now",
35		"Concentrate and ask again",
36		"Don't count on it",
37		"My reply is no",
38		"My sources say no",
39		"Outlook not so good",
40		"Very doubtful",
41	}
42	fmt.Println("Magic 8-Ball says:", answers[rand.IntN(len(answers))])
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.
47func Example_rand() {
48	// Create and seed the generator.
49	// Typically a non-fixed seed should be used, such as Uint64(), Uint64().
50	// Using a fixed seed will produce the same output on every run.
51	r := rand.New(rand.NewPCG(1, 2))
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 any) {
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	// Int32, Int64, and Uint32 generate values of the given width.
71	// The Int method (not shown) is like either Int32 or Int64
72	// depending on the size of 'int'.
73	show("Int32", r.Int32(), r.Int32(), r.Int32())
74	show("Int64", r.Int64(), r.Int64(), r.Int64())
75	show("Uint32", r.Uint32(), r.Uint32(), r.Uint32())
76
77	// IntN, Int32N, and Int64N 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("Int32N(10)", r.Int32N(10), r.Int32N(10), r.Int32N(10))
81	show("Int64N(10)", r.Int64N(10), r.Int64N(10), r.Int64N(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     0.95955694          0.8076733            0.8135684
87	// Float64     0.4297927436037299  0.797802349388613    0.3883664855410056
88	// ExpFloat64  0.43463410545541104 0.5513632046504593   0.7426404617374481
89	// NormFloat64 -0.9303318111676635 -0.04750789419852852 0.22248301107582735
90	// Int32       2020777787          260808523            851126509
91	// Int64       5231057920893523323 4257872588489500903  158397175702351138
92	// Uint32      314478343           1418758728           208955345
93	// IntN(10)    6                   2                    0
94	// Int32N(10)  3                   7                    7
95	// Int64N(10)  8                   9                    4
96	// Perm        [0 3 1 4 2]         [4 1 2 0 3]          [4 3 2 0 1]
97}
98
99func ExamplePerm() {
100	for _, value := range rand.Perm(3) {
101		fmt.Println(value)
102	}
103
104	// Unordered output: 1
105	// 2
106	// 0
107}
108
109func ExampleN() {
110	// Print an int64 in the half-open interval [0, 100).
111	fmt.Println(rand.N(int64(100)))
112
113	// Sleep for a random duration between 0 and 100 milliseconds.
114	time.Sleep(rand.N(100 * time.Millisecond))
115}
116
117func ExampleShuffle() {
118	words := strings.Fields("ink runs from the corners of my mouth")
119	rand.Shuffle(len(words), func(i, j int) {
120		words[i], words[j] = words[j], words[i]
121	})
122	fmt.Println(words)
123}
124
125func ExampleShuffle_slicesInUnison() {
126	numbers := []byte("12345")
127	letters := []byte("ABCDE")
128	// Shuffle numbers, swapping corresponding entries in letters at the same time.
129	rand.Shuffle(len(numbers), func(i, j int) {
130		numbers[i], numbers[j] = numbers[j], numbers[i]
131		letters[i], letters[j] = letters[j], letters[i]
132	})
133	for i := range numbers {
134		fmt.Printf("%c: %c\n", letters[i], numbers[i])
135	}
136}
137
138func ExampleIntN() {
139	fmt.Println(rand.IntN(100))
140	fmt.Println(rand.IntN(100))
141	fmt.Println(rand.IntN(100))
142}
143