Optimize Key.Strings by reducing memory re-allocations and simplifying control flow (#385)

bench_test.go

@@ -114,3 +114,16 @@ func Benchmark_Key_SetValue_VisSection(b *testing.B) {
 		sec.Key("NAME").SetValue("10")
 	}
 }
+
+func Benchmark_Key_Strings_LargeArray(b *testing.B) {
+	c, err := Load("testdata/large_array.ini")
+	if err != nil {
+		b.Fatal(err)
+	}
+	key := c.Section("").Key("ARRAY")
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_ = key.Strings(",")
+	}
+}

key.go

@@ -15,12 +15,12 @@
 package ini
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"strconv"
 	"strings"
 	"time"
+	"unicode/utf8"
 )
 
 // Key represents a key under a section.
@@ -495,31 +495,38 @@ func (k *Key) Strings(delim string) []string {
 		return []string{}
 	}
 
-	runes := []rune(str)
-	vals := make([]string, 0, 2)
-	var buf bytes.Buffer
-	escape := false
-	idx := 0
+	maxParts := strings.Count(str, delim) + 1
+	vals := make([]string, 0, maxParts)
+
+	var buf strings.Builder
+	buf.Grow(len(str))
+
+	i := 0
 	for {
-		if escape {
-			escape = false
-			if runes[idx] != '\\' && !strings.HasPrefix(string(runes[idx:]), delim) {
+		if str[i] == '\\' {
+			i++
+			if i >= len(str) {
+				break
+			}
+
+			if str[i] != '\\' && !strings.HasPrefix(str[i:], delim) {
 				buf.WriteRune('\\')
 			}
-			buf.WriteRune(runes[idx])
-		} else {
-			if runes[idx] == '\\' {
-				escape = true
-			} else if strings.HasPrefix(string(runes[idx:]), delim) {
-				idx += len(delim) - 1
+
+			r, size := utf8.DecodeRuneInString(str[i:])
+			i += size
+			buf.WriteRune(r)
+		} else if strings.HasPrefix(str[i:], delim) {
+			i += len(delim)
 			vals = append(vals, strings.TrimSpace(buf.String()))
 			buf.Reset()
 		} else {
-				buf.WriteRune(runes[idx])
+			r, size := utf8.DecodeRuneInString(str[i:])
+			i += size
+			buf.WriteRune(r)
 		}
-		}
-		idx++
-		if idx == len(runes) {
+
+		if i >= len(str) {
 			break
 		}
 	}