I'm programming a generic cache mechanism and i need to set some attributes in a struct knowing only their reflect.Type, attribute name and reflect.Value to be setted in the attribute, but i can't avoid the type assertion, that makes my code not generic...
func main() {
addressNew := Address{"New Address description!"}
// In the real problem, i know the reflect.Type of value, but
// the struct came to me as a interface{}, just like this method
// Return many kinds of values from redis as interface{},
// (Customer, Order, Address, Product, SKU etc), in a generic way,
// but returns the reflect.Type of value also.
interfaceSomeValue := getMyValue()
fmt.Printf("%v", interfaceSomeValue)
fmt.Println("")
// This portion of code comes from my cache mechanism, that is a library
// used by other projects. My cache lib really can't know all others
// type structs to perform the type assertion, but the cache mechanism know
// the reflect.Type of the interface.
// If you try at this way, will cause a panic by try to access a FieldByName
// in a interface, because the Customer comes from getMyValue and
// becomes a interface{}, and now a type assertion is
// required -> http://play.golang.org/p/YA8U9_KzC9
newCustomerNewAttribute := SetAttribute(&interfaceSomeValue, "Local", interface{}(addressNew), reflect.TypeOf(Customer{}))
fmt.Printf("%v", newCustomerNewAttribute)
fmt.Println("")
}
func SetAttribute(object interface{}, attributeName string, attValue interface{}, objectType reflect.Type) interface{} {
if reflect.ValueOf(object).Kind() != reflect.Ptr {
panic("need a pointer")
}
value := reflect.ValueOf(object).Elem()
field := value.FieldByName(attributeName)
valueForAtt := reflect.ValueOf(attValue)
field.Set(valueForAtt)
return value.Interface()
}
Go Playground for the problem (works by hard coded type assertion)...
Go Playground for the problem (doesn't work with an unknown interface)
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