small string split join optimization

internal/utils/strutils/split_join.go

@@ -0,0 +1,81 @@
+package strutils
+
+import (
+	"math"
+	"strings"
+)
+
+// SplitRune is like strings.Split but takes a rune as separator.
+func SplitRune(s string, sep rune) []string {
+	if sep == 0 {
+		return strings.Split(s, "")
+	}
+	n := strings.Count(s, string(sep)) + 1
+	if n > len(s)+1 {
+		n = len(s) + 1
+	}
+	a := make([]string, n)
+	n--
+	i := 0
+	for i < n {
+		m := strings.IndexRune(s, sep)
+		if m < 0 {
+			break
+		}
+		a[i] = s[:m]
+		s = s[m+1:]
+		i++
+	}
+	a[i] = s
+	return a[:i+1]
+}
+
+// SplitComma is a wrapper around SplitRune(s, ',').
+func SplitComma(s string) []string {
+	return SplitRune(s, ',')
+}
+
+// SplitLine is a wrapper around SplitRune(s, '\n').
+func SplitLine(s string) []string {
+	return SplitRune(s, '\n')
+}
+
+// SplitSpace is a wrapper around SplitRune(s, ' ').
+func SplitSpace(s string) []string {
+	return SplitRune(s, ' ')
+}
+
+// JoinRune is like strings.Join but takes a rune as separator.
+func JoinRune(elems []string, sep rune) string {
+	switch len(elems) {
+	case 0:
+		return ""
+	case 1:
+		return elems[0]
+	}
+	if sep == 0 {
+		return strings.Join(elems, "")
+	}
+
+	var n int
+	for _, elem := range elems {
+		if len(elem) > math.MaxInt-n {
+			panic("strings: Join output length overflow")
+		}
+		n += len(elem)
+	}
+
+	var b strings.Builder
+	b.Grow(n)
+	b.WriteString(elems[0])
+	for _, s := range elems[1:] {
+		b.WriteRune(sep)
+		b.WriteString(s)
+	}
+	return b.String()
+}
+
+// JoinLines is a wrapper around JoinRune(elems, '\n').
+func JoinLines(elems []string) string {
+	return JoinRune(elems, '\n')
+}