MINOR: dashcase rewrite for performance

misc/stringutil.go

@@ -109,38 +109,32 @@ func SnakeCase(fieldName string) string {
 }
 
 // DashCase turns camel case to snake case string
-func DashCase(fieldName string) string {
-	fieldName = strings.Trim(fieldName, " ")
-	n := ""
-	for i, v := range fieldName {
-		// treat acronyms as words, eg for JSONData -> JSON is a whole word
-		nextCaseIsChanged := false
-		if i+1 < len(fieldName) {
-			next := fieldName[i+1]
-			if (v >= 'A' && v <= 'Z' && next >= 'a' && next <= 'z') || (v >= 'a' && v <= 'z' && next >= 'A' && next <= 'Z') {
-				nextCaseIsChanged = true
+func DashCase(input string) string {
+	var result strings.Builder
+	n := len(input)
+	// Grow to worst case where a dash is inserted every character.
+	result.Grow(n * 2)
+
+	for i, r := range input {
+		// if r is capital ..
+		if r >= 'A' && r <= 'Z' {
+			// add a dash  before if :
+			// 1. we're not on the first or last character.
+			// 2. the previous character is not capital.
+			// 3. the next character is not capital.
+			// To understand the rules take "JSONData" -> "json-data" as an example
+			if i > 0 && !(input[i-1] >= 'A' && input[i-1] <= 'Z' && (i+1 == n || i+1 < n && input[i+1] >= 'A' && input[i+1] <= 'Z')) {
+				result.WriteByte('-')
 			}
-		}
-
-		switch {
-		case i > 0 && n[len(n)-1] != '-' && nextCaseIsChanged:
-			// add underscore if next letter case type is changed
-			if v >= 'A' && v <= 'Z' {
-				n += "-" + string(v)
-			} else if v >= 'a' && v <= 'z' {
-				n += string(v) + "-"
-			}
-		case v == ' ':
-			// replace spaces with underscores
-			n += "-"
-		default:
-			n += string(v)
+			// Lower the case of the character
+			result.WriteByte(byte(r + ('a' - 'A')))
+		} else {
+			// If lowercase just write it
+			result.WriteRune(r)
 		}
 	}
-	n = strings.ToLower(n)
-	// special case
-	n = strings.ReplaceAll(n, "httpuri", "http-uri")
-	return n
+
+	return strings.ReplaceAll(result.String(), "httpuri", "http-uri")
 }
 
 func ParseSize(size string) *int64 {