util/reflect: add useful helpers

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

util/reflect/reflect.go

@@ -81,3 +81,41 @@ func StructFields(src interface{}) ([]reflect.StructField, error) {
 
 	return fields, nil
 }
+
+// CopyDefaults for a from b
+// a and b should be pointers to the same kind of struct
+func CopyDefaults(a, b interface{}) {
+	pt := reflect.TypeOf(a)
+	t := pt.Elem()
+	va := reflect.ValueOf(a).Elem()
+	vb := reflect.ValueOf(b).Elem()
+	for i := 0; i < t.NumField(); i++ {
+		aField := va.Field(i)
+		if aField.CanSet() {
+			bField := vb.Field(i)
+			aField.Set(bField)
+		}
+	}
+}
+
+// CopyFrom sets the public members of a from b
+// a and b should be pointers to structs
+// a can be a different type from b
+// Only the Fields which have the same name and assignable type on a
+// and b will be set.
+func CopyFrom(a, b interface{}) {
+	ta := reflect.TypeOf(a).Elem()
+	tb := reflect.TypeOf(b).Elem()
+	va := reflect.ValueOf(a).Elem()
+	vb := reflect.ValueOf(b).Elem()
+	for i := 0; i < tb.NumField(); i++ {
+		bField := vb.Field(i)
+		tbField := tb.Field(i)
+		name := tbField.Name
+		aField := va.FieldByName(name)
+		taField, found := ta.FieldByName(name)
+		if found && aField.IsValid() && bField.IsValid() && aField.CanSet() && tbField.Type.AssignableTo(taField.Type) {
+			aField.Set(bField)
+		}
+	}
+}