improved the generated code by using maps and using existing String method if available

example/shirtsize_jsonenums.go

@@ -7,34 +7,23 @@ import (
 	"fmt"
 )
 
-func (r ShirtSize) String() string {
+var _ShirtSizeValueToName = map[ShirtSize]string{
-	switch r {
+	NA: "NA", XS: "XS", S: "S", M: "M", L: "L", XL: "XL",
-
-	case NA:
-		return "NA"
-
-	case XS:
-		return "XS"
-
-	case S:
-		return "S"
-
-	case M:
-		return "M"
-
-	case L:
-		return "L"
-
-	case XL:
-		return "XL"
-
-	default:
-		return "unknown ShirtSize"
-	}
 }
 
 func (r ShirtSize) MarshalJSON() ([]byte, error) {
-	return json.Marshal(r.String())
+	if s, ok := r.(fmt.Stringer); ok {
+		return json.Marshal(s.String())
+	}
+	s, ok := _ShirtSizeValueToName[r]
+	if !ok {
+		return nil, fmt.Errorf("invalid ShirtSize: %d", r)
+	}
+	return json.Marshal(s)
+}
+
+var _ShirtSizeNameToValue = map[string]ShirtSize{
+	"NA": NA, "XS": XS, "S": S, "M": M, "L": L, "XL": XL,
 }
 
 func (r *ShirtSize) UnmarshalJSON(data []byte) error {
@@ -42,28 +31,10 @@ func (r *ShirtSize) UnmarshalJSON(data []byte) error {
 	if err := json.Unmarshal(data, &s); err != nil {
 		return fmt.Errorf("ShirtSize should be a string, got %s", data)
 	}
-	switch s {
+	v, ok := _ShirtSizeNameToValue[s]
-
+	if !ok {
-	case "NA":
-		*r = NA
-
-	case "XS":
-		*r = XS
-
-	case "S":
-		*r = S
-
-	case "M":
-		*r = M
-
-	case "L":
-		*r = L
-
-	case "XL":
-		*r = XL
-
-	default:
 		return fmt.Errorf("invalid ShirtSize %q", s)
 	}
+	*r = v
 	return nil
 }

example/weekday_jsonenums.go

@@ -7,37 +7,23 @@ import (
 	"fmt"
 )
 
-func (r WeekDay) String() string {
+var _WeekDayValueToName = map[WeekDay]string{
-	switch r {
+	Monday: "Monday", Tuesday: "Tuesday", Wednesday: "Wednesday", Thursday: "Thursday", Friday: "Friday", Saturday: "Saturday", Sunday: "Sunday",
-
-	case Monday:
-		return "Monday"
-
-	case Tuesday:
-		return "Tuesday"
-
-	case Wednesday:
-		return "Wednesday"
-
-	case Thursday:
-		return "Thursday"
-
-	case Friday:
-		return "Friday"
-
-	case Saturday:
-		return "Saturday"
-
-	case Sunday:
-		return "Sunday"
-
-	default:
-		return "unknown WeekDay"
-	}
 }
 
 func (r WeekDay) MarshalJSON() ([]byte, error) {
-	return json.Marshal(r.String())
+	if s, ok := r.(fmt.Stringer); ok {
+		return json.Marshal(s.String())
+	}
+	s, ok := _WeekDayValueToName[r]
+	if !ok {
+		return nil, fmt.Errorf("invalid WeekDay: %d", r)
+	}
+	return json.Marshal(s)
+}
+
+var _WeekDayNameToValue = map[string]WeekDay{
+	"Monday": Monday, "Tuesday": Tuesday, "Wednesday": Wednesday, "Thursday": Thursday, "Friday": Friday, "Saturday": Saturday, "Sunday": Sunday,
 }
 
 func (r *WeekDay) UnmarshalJSON(data []byte) error {
@@ -45,31 +31,10 @@ func (r *WeekDay) UnmarshalJSON(data []byte) error {
 	if err := json.Unmarshal(data, &s); err != nil {
 		return fmt.Errorf("WeekDay should be a string, got %s", data)
 	}
-	switch s {
+	v, ok := _WeekDayNameToValue[s]
-
+	if !ok {
-	case "Monday":
-		*r = Monday
-
-	case "Tuesday":
-		*r = Tuesday
-
-	case "Wednesday":
-		*r = Wednesday
-
-	case "Thursday":
-		*r = Thursday
-
-	case "Friday":
-		*r = Friday
-
-	case "Saturday":
-		*r = Saturday
-
-	case "Sunday":
-		*r = Sunday
-
-	default:
 		return fmt.Errorf("invalid WeekDay %q", s)
 	}
+	*r = v
 	return nil
 }

template.go

@@ -19,19 +19,23 @@ import (
 )
 
 {{range $typename, $values := .TypesAndValues}}
-func (r {{$typename}}) String() string {
+var _{{$typename}}ValueToName = map[{{$typename}}]string {
-    switch r {
+    {{range $values}}{{.}}: "{{.}}",{{end}}
-    {{range $values}}
-    case {{.}}:
-        return "{{.}}"
-    {{end}}
-    default:
-        return "unknown {{$typename}}"
-    }
 }
 
 func (r {{$typename}}) MarshalJSON() ([]byte, error) {
-    return json.Marshal(r.String())
+    if s, ok := r.(fmt.Stringer); ok {
+        return json.Marshal(s.String())
+    }
+    s, ok := _{{$typename}}ValueToName[r]
+    if !ok {
+        return nil, fmt.Errorf("invalid {{$typename}}: %d", r)
+    }
+    return json.Marshal(s)
+}
+
+var _{{$typename}}NameToValue = map[string]{{$typename}} {
+    {{range $values}}"{{.}}": {{.}},{{end}}
 }
 
 func (r *{{$typename}}) UnmarshalJSON(data []byte) error {
@@ -39,14 +43,11 @@ func (r *{{$typename}}) UnmarshalJSON(data []byte) error {
     if err := json.Unmarshal(data, &s); err != nil {
         return fmt.Errorf("{{$typename}} should be a string, got %s", data)
     }
-    switch s {
+    v, ok := _{{$typename}}NameToValue[s]
-    {{range $values}}
+    if !ok {
-    case "{{.}}":
-        *r = {{.}}
-    {{end}}
-    default:
         return fmt.Errorf("invalid {{$typename}} %q", s)
     }
+    *r = v
     return nil
 }