Add RandomString (#266)

* Add RandomString

* PR update

README.md

@@ -143,6 +143,7 @@ Supported math helpers:
 
 Supported helpers for strings:
 
+- [RandomString](#randomstring)
 - [Substring](#substring)
 - [ChunkString](#chunkstring)
 - [RuneLength](#runelength)
@@ -1207,6 +1208,17 @@ sum := lo.SumBy(strings, func(item string) int {
 
 [[play](https://go.dev/play/p/Dz_a_7jN_ca)]
 
+### RandomString
+
+Returns a random string of the specified length and made of the specified charset.
+
+```go
+str := lo.RandomString(5, lo.LettersCharset)
+// example: "eIGbt"
+```
+
+[[play](https://go.dev/play/p/rRseOQVVum4)]
+
 ### Substring
 
 Return part of a string.

string.go

@@ -1,9 +1,38 @@
 package lo
 
 import (
+	"math/rand"
 	"unicode/utf8"
 )
 
+var (
+	LowerCaseLettersCharset = []rune("abcdefghijklmnopqrstuvwxyz")
+	UpperCaseLettersCharset = []rune("ABCDEFGHIJKLMNOPQRSTUVWXYZ")
+	LettersCharset          = append(LowerCaseLettersCharset, UpperCaseLettersCharset...)
+	NumbersCharset          = []rune("0123456789")
+	AlphanumericCharset     = append(LettersCharset, NumbersCharset...)
+	SpecialCharset          = []rune("!@#$%^&*()_+-=[]{}|;':\",./<>?")
+	AllCharset              = append(AlphanumericCharset, SpecialCharset...)
+)
+
+// RandomString return a random string.
+// Play: https://go.dev/play/p/rRseOQVVum4
+func RandomString(size int, charset []rune) string {
+	if size <= 0 {
+		panic("lo.RandomString: Size parameter must be greater than 0")
+	}
+	if len(charset) <= 0 {
+		panic("lo.RandomString: Charset parameter must not be empty")
+	}
+
+	b := make([]rune, size)
+	possibleCharactersCount := len(charset)
+	for i := range b {
+		b[i] = charset[rand.Intn(possibleCharactersCount)]
+	}
+	return string(b)
+}
+
 // Substring return part of a string.
 // Play: https://go.dev/play/p/TQlxQi82Lu1
 func Substring[T ~string](str T, offset int, length uint) T {

string_test.go

@@ -2,11 +2,35 @@ package lo
 
 import (
 	"math"
+	"math/rand"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
 
+func TestRandomString(t *testing.T) {
+	t.Parallel()
+	is := assert.New(t)
+
+	rand.Seed(time.Now().UnixNano())
+
+	str1 := RandomString(100, LowerCaseLettersCharset)
+	is.Equal(100, RuneLength(str1))
+	is.Subset(LowerCaseLettersCharset, []rune(str1))
+
+	str2 := RandomString(100, LowerCaseLettersCharset)
+	is.NotEqual(str1, str2)
+
+	noneUtf8Charset := []rune("明1好休2林森")
+	str3 := RandomString(100, noneUtf8Charset)
+	is.Equal(100, RuneLength(str3))
+	is.Subset(noneUtf8Charset, []rune(str3))
+
+	is.PanicsWithValue("lo.RandomString: Charset parameter must not be empty", func() { RandomString(100, []rune{}) })
+	is.PanicsWithValue("lo.RandomString: Size parameter must be greater than 0", func() { RandomString(0, LowerCaseLettersCharset) })
+}
+
 func TestChunkString(t *testing.T) {
 	t.Parallel()
 	is := assert.New(t)