feat(Enc): allows the caller to change the tag used to locate custom field aliases

query/encode.go

@@ -110,7 +110,12 @@ type Encoder interface {
 //
 // Multiple fields that encode to the same URL parameter name will be included
 // as multiple URL values of the same name.
+
 func Values(v interface{}) (url.Values, error) {
+	return values(v, "url")
+}
+
+func values(v interface{}, tag string) (url.Values, error) {
 	values := make(url.Values)
 	val := reflect.ValueOf(v)
 	for val.Kind() == reflect.Ptr {
@@ -128,14 +133,33 @@ func Values(v interface{}) (url.Values, error) {
 		return nil, fmt.Errorf("query: Values() expects struct input. Got %v", val.Kind())
 	}
 
-	err := reflectValue(values, val, "")
-	return values, err
+	err := reflectValue(values, val, "", tag)
+	return values, err	
+}
+
+
+type Enc struct{
+	tag string
 }
 
+func NewEncoder()*Enc{
+	return &Enc{tag: "url"}
+}
+
+// SetAliasTag changes the tag used to locate custom field aliases. The default tag is "url".
+func(e *Enc)SetAliasTag(tag string)*Enc{
+	e.tag = tag
+	return e
+}
+
+func (e *Enc)Values(v interface{}) (url.Values, error){
+	return values(v, e.tag)
+} 
+
 // reflectValue populates the values parameter from the struct fields in val.
 // Embedded structs are followed recursively (using the rules defined in the
 // Values function documentation) breadth-first.
-func reflectValue(values url.Values, val reflect.Value, scope string) error {
+func reflectValue(values url.Values, val reflect.Value, scope, tagSel string) error {
 	var embedded []reflect.Value
 
 	typ := val.Type()
@@ -146,7 +170,7 @@ func reflectValue(values url.Values, val reflect.Value, scope string) error {
 		}
 
 		sv := val.Field(i)
-		tag := sf.Tag.Get("url")
+		tag := sf.Tag.Get(tagSel)
 		if tag == "-" {
 			continue
 		}
@@ -230,15 +254,15 @@ func reflectValue(values url.Values, val reflect.Value, scope string) error {
 		}
 
 		if sv.Kind() == reflect.Struct {
-			reflectValue(values, sv, name)
+			reflectValue(values, sv, name, tagSel)
 			continue
 		}
 
 		values.Add(name, valueString(sv, opts))
 	}
 
 	for _, f := range embedded {
-		if err := reflectValue(values, f, scope); err != nil {
+		if err := reflectValue(values, f, scope, tagSel); err != nil {
 			return err
 		}
 	}

query/encode_test.go

@@ -171,6 +171,42 @@ func TestValues_types(t *testing.T) {
 	}
 }
 
+func TestEnc(t *testing.T){
+	var tests = []struct{
+		in interface{}
+		want url.Values
+	}{
+		{
+			in:	struct{
+				C []string `xyz:"a"`
+			}{
+				C: []string{"a", "b"},
+			},
+			want:	url.Values{"a":   {"a", "b"},},
+		},
+		{
+			in:	struct{
+				C []string 
+			}{
+				C: []string{"a", "b"},
+			},
+			want:	url.Values{"C":   {"a", "b"},},
+		},
+
+	}
+	for i, tt := range tests {
+		en := NewEncoder().SetAliasTag("xyz")
+		v, err := en.Values(tt.in)
+		if err != nil {
+			t.Errorf("%d. Values(%q) returned error: %v", i, tt.in, err)
+		}
+
+		if !reflect.DeepEqual(tt.want, v) {
+			t.Errorf("%d. Enc(%q) returned %v, want %v", i, tt.in, v, tt.want)
+		}
+	}	
+}
+
 func TestValues_omitEmpty(t *testing.T) {
 	str := ""
 	s := struct {