fix: substring support utf8 character (#327)

string.go

@@ -2,6 +2,7 @@ package lo
 
 import (
 	"math/rand"
+	"strings"
 	"unicode/utf8"
 )
 
@@ -36,7 +37,8 @@ func RandomString(size int, charset []rune) string {
 // Substring return part of a string.
 // Play: https://go.dev/play/p/TQlxQi82Lu1
 func Substring[T ~string](str T, offset int, length uint) T {
-	size := len(str)
+	rs := []rune(str)
+	size := len(rs)
 
 	if offset < 0 {
 		offset = size + offset
@@ -53,7 +55,7 @@ func Substring[T ~string](str T, offset int, length uint) T {
 		length = uint(size - offset)
 	}
 
-	return str[offset : offset+int(length)]
+	return T(strings.Replace(string(rs[offset:offset+int(length)]), "\x00", "", -1))
 }
 
 // ChunkString returns an array of strings split into groups the length of size. If array can't be split evenly,

string_test.go

@@ -74,6 +74,7 @@ func TestSubstring(t *testing.T) {
 	str10 := Substring("hello", -2, 4)
 	str11 := Substring("hello", -4, 1)
 	str12 := Substring("hello", -4, math.MaxUint)
+	str13 := Substring("🏠🐶🐱", 0, 2)
 
 	is.Equal("", str1)
 	is.Equal("", str2)
@@ -87,6 +88,7 @@ func TestSubstring(t *testing.T) {
 	is.Equal("lo", str10)
 	is.Equal("e", str11)
 	is.Equal("ello", str12)
+	is.Equal("🏠🐶", str13)
 }
 
 func TestRuneLength(t *testing.T) {