How can I abstract that a methods has optional parameters?
abstract class CopyWith<T>{
T copyWith({}); // Error : Expected an identifier.
}
If I add an identifier like {test} it works and subclasses can have additional arguments
What I want to achieve?
I have a complex state manager, I make some abstraction , the following code is a minimal code, show my problem
import 'dart:collection';
abstract class CopyWith<T> {
T copyWith(OPTIONAL_NAMED_ARGUMENTS);
}
abstract class Manager<K, V extends CopyWith> {
final _map = HashMap<K, V>();
add(K key,V value){
_map[key] = value;
}
void copyWith(K key,OPTIONAL_NAMED_ARGUMENTS) {
assert(key != null);
if (_map.containsKey(key)) {
_map[key].copyWith(OPTIONAL_NAMED_ARGUMENTS);
}
}
}
class User implements CopyWith {
final int id;
final String name;
User({this.id, this.name});
User copyWith({int id, String name}) {
return User(
id: id ?? this.id,
name: name ?? this.name,
);
}
}
class UserManager extends Manager<int, User> {}
void main() {
final userManager = UserManager();
userManager.add(1,User(1,'test'));
userManager.copyWith(1,{test:'test2'})
}
As some one who has faced this issue in my library, I would say the only way is to not put a copyWith in your base class.
Why? Because you should only make a function polymorphic when there IS actually a shared calling convention and behavior. In your example, The way that these two classes perform copyWith is just different. It is, and should be, an error to send a name to Manager.copyWith, because Manager does not have a name to begin with. If you encounter a name inside a Manager.copyWith, that means there is some serious error in your code.
Also, if you actually try to invoke copyWith, as a responsible programmer, you will probably check if you are allowed to pass a name, which is,
if (someObj is User) {
someObj.copyWith(key, name: name);
} else if (someObj is Manager) {
throw IllegalStateError('You should not pass a name to a Manager! What am I supposed to do with the name now?');
}
There, you have already done type checking, so no need to make copyWith polymorphic.
However, some common behaviors can be made polymorphic, like updateKey. You can make Keyable as an interface, and Keyable updateKey(Key key) as an abstract method, and delegate to a non-polymorphic copyWith inside each subclasses.
Related
I'm trying to have a base Freezed interface which my app entity interfaces can extend so I can call the freezed functions on the interfaces. I've started the process here which seems to be working so far:
abstract class IUserRegistrationEntity<T> extends FreezedClass<T> {
String get nickName;
String get email;
String get confirmEmail;
String get password;
String get confirmPassword;
}
abstract class FreezedClass<T> {
T get copyWith;
Map<String, dynamic> toJson();
}
freezed class:
import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:vepo/domain/user_registration/i_user_registration_entity.dart';
part 'user_registration_entity.freezed.dart';
part 'user_registration_entity.g.dart';
#freezed
abstract class UserRegistrationEntity with _$UserRegistrationEntity {
#Implements.fromString(
'IUserRegistrationEntity<\$UserRegistrationEntityCopyWith<IUserRegistrationEntity>>')
const factory UserRegistrationEntity(
{String nickName,
String email,
String confirmEmail,
String password,
String confirmPassword}) = _IUserRegistrationEntity;
factory UserRegistrationEntity.fromJson(Map<String, dynamic> json) =>
_$UserRegistrationEntityFromJson(json);
}
But now I need to add the fromJson factory constructor to the interface. I think this may be what I'm looking for although I can't really tell how to implement it in my code:
T deserialize<T extends JsonSerializable>(
String json,
T factory(Map<String, dynamic> data),
) {
return factory(jsonDecode(json) as Map<String, dynamic>);
}
You an then call it with:
var myValue = deserialize(jsonString, (x) => MyClass.fromJson(x));
Any help adding the fromJson to my freezed interface would be appreciated.
I've found a way to get the same benefits of programming to an interface or "abstraction" with freezed objects, while still getting to call those freezed functions:
#freezed
abstract class Person with _$Person {
#With(BasicPersonMixin)
const factory Person.basicPerson(
{int? id, String? firstName, String? lastName}) = BasicPerson;
#With(FancyPersonMixin)
const factory Person.fancyPerson({String? firstName, required String extraPropMiddleName, String? lastName}) =
FancyPerson;
factory Person.fromJson(Map<String, dynamic> json) => _$PersonFromJson(json);
const Person._();
void functionThatEveryPersonShares() {
print('I am a person');
}
String greet() {
return 'override me with a mixin or abstract class';
}
}
mixin FancyPersonMixin {
String get extraPropMiddleName {
return 'my default middle name is John`;
}
String greet() {
return 'Salutations!';
}
void specialisedFunctionThatOnlyIHave() {
print('My middle name is $extraPropMiddleName');
}
}
mixin BasicPersonMixin {
String greet() {
return 'Hi.';
}
}
Now we have 2 concrete classes: BasicPerson, and FancyPerson which are both a Person. Now we can program to Person throughout the app, and still call .copyWith and .fromJson and so on and so forth. The different types of Person can vary independently from each other by using mixins and still be used as a Person type. Works with generics etc (from docs - #With.fromString('AdministrativeArea<House>')) but I have kept the example simple for this question to most simply show the benefits. You can also make Person extend another base class.
I've found another way to let you be a bit more abstract than my other answer. Say you're in a highly abstract super-class, so you don't want to work with objects as specific as Person. You want to work with "a base freezed object"; just cast your type to dynamic in brackets and go ahead and use copyWith freely. Sure, it's not typesafe, but it's a worthy option if it allows you to do something in a super-class rather than in every sub-class.
mixin LocalSaveMixin<TEntity extends LocalSaveMixin<TEntity>> on Entity {
LocalRepository<TEntity> get $repository;
Ref? get provider;
TEntity $localFetch() {
return ($repository.$localFetch() as dynamic).copyWith(provider: provider)
as TEntity;
}
TEntity $localSave() {
return $repository.$localSave(entity: this as TEntity);
}
}
I am trying to create a base class for my models but I am struggling with the error The name 'cls' isn't a type so it can't be used as a type argument.. So, how can I pass the object's constructor to the Hive.box method?
import 'package:hive/hive.dart';
class AppModel {
#HiveField(0)
int id;
#HiveField(1)
DateTime createdAt;
#HiveField(2)
DateTime updatedAt;
save() async {
final Type cls = this.runtimeType;
// The name 'cls' isn't a type so it can't be used as a type argument.
final Box box = await Hive.openBox<cls>(cls.toString());
await box.put(this.id, this);
return this;
}
}
#HiveType(typeId: 0)
class UserModel extends AppModel {
#HiveField(3)
String email;
#HiveField(4)
String displayName;
}
void main() {
final UserModel user = UserModel()
..email = 'user#domain.com'
..displayName = 'john doe';
user.save().then(() {
print('saved');
});
}
Dart does not have a way to refer to the dynamic type of this (a "self type").
The way such things are often handled is to have a self-type as type argument, so:
class AppModel<T extends AppModel> {
save() async {
final Box box = await Hive.openBox<T>(T.toString());
await box.put(this.id, this as T);
return this;
}
...
and then ensure that each subclass tells the superclass what type it is:
class UserModel extends AppModel<UserModel> {
...
}
(or, if you expect to subclass UserModel eventually:
class UserModel<T extends UserModel> extends AppModel<T> {
...
}
so that a subclass can still pass its type through).
You are also talking about constructors, and for that there is no easy solution.
Dart's type parameters are types, not classes. You cannot access static members or constructors from a type variable, and there is also no other way to pass a class around.
The only way you can have something call a constructor that it doesn't refer to statically, is to wrap the constructor call in a function and pass that function.
(I can't see how you need the constructor here).
A few times now I've run into a use case where I need to define an interface for how classes construct themselves. One such example could be if I want to make an Interface Class that defines the interface by which objects can serialize and unserialize themselves (for input into a database, to be sent as JSON, etc). You might write something like this:
abstract class Serializable {
String serialize();
Serializable unserialize(String serializedString);
}
But now you have a problem, as serialize() is properly an instance method, and unserialize() should instead be a static method (which isn't inheritable or enforced by the Interface) or a constructor (which also isn't inheritable).
This leaves a state where classes that impliment the Serializable interface are required to define a serialize() method, but there is no way to require those classes to define a static unserialize() method or Foo.fromSerializedString() constructor.
If you make unserialize() an instance method, then unserializing an implementing class Foo would look like:
Foo foo = new Foo();
foo = foo.unserialize(serializedString);
which is rather cumbersome and ugly.
The only other option I can think of is to add a comment in the Serializable interface asking nicely that implementing classes define the appropriate static method or constructor, but this is obviously prone to error if a developer misses it and also hurts code completion.
So, is there a better way to do this? Is there some pattern by which you can have an interface which forces implementing classes to define a way to construct themselves, or something that gives that general effect?
You will have to use instance methods if you want the inheritance guarantees. You can do a bit nicer than manual instantiation though, by using reflection.
abstract class Serializable {
static Serializable fromSerializedString(Type type, String serializedString) {
ClassMirror cm = reflectClass(type);
InstanceMirror im = cm.newInstance(const Symbol(''), []);
var obj = im.reflectee;
obj.unserialize(serializedString);
return obj;
}
String serialize();
void unserialize(String serializedString);
}
Now if someone implements Serializable they will be forced to provide an unserialize method:
class Foo implements Serializable {
#override
String serialize() {
// TODO: implement serialize
}
#override
void unserialize(String string) {
// TODO: implement unserialize
}
}
You can get an instance like so:
var foo = Serializable.fromSerializedString(Foo, 'someSerializedString');
This might be a bit prettier and natural than the manual method, but keep in mind that it uses reflection with all the problems that can entail.
If you decide to go with a static method and a warning comment instead, it might be helpful to also provide a custom Transformer that scans through all classes implementing Serializable and warn the user or stops the build if any don't have a corresponding static unserialize method or constructor (similar to how Polymer does things). This obviously wouldn't provide the instant feedback the an editor could with instance methods, but would be more visible than a simple comment in the docs.
I think this example is a more Dart-like way to implement the encoding and decoding. In practice I don't think "enforcing" the decode signature will actually help catch bugs, or improve code quality. If you need to make the decoder types pluggable then you can make the decoders map configurable.
const Map<String,Function> _decoders = const {
'foo': Foo.decode,
'bar': Bar.decode
};
Object decode(String s) {
var obj = JSON.decode(s);
var decoder = _decoders[obj['type']];
return decoder(s);
}
abstract class Encodable {
abstract String encode();
}
class Foo implements Encodable {
encode() { .. }
static Foo decode(String s) { .. }
}
class Bar implements Encodable {
encode() { .. }
static Foo decode(String s) { .. }
}
main() {
var foo = decode('{"type": "foo", "i": 42}');
var bar = decode('{"type": "bar", "k": 43}');
}
A possible pattern I've come up with is to create a Factory class that utilize instance methods in a slightly less awkward way. Something like follows:
typedef Constructable ConstructorFunction();
abstract class Constructable {
ConstructorFunction constructor;
}
abstract class Serializable {
String serialize();
Serializable unserialize(String serializedString);
}
abstract class SerializableModel implements Serializable, Constructable {
}
abstract class ModelFactory extends Model {
factory ModelFactory(ConstructorFunction constructor) {
return constructor();
}
factory ModelFactory.fromSerializedString(ConstructorFunction constructor, String serializedString) {
Serializable object = constructor();
return object.unserialize(serializedString);
}
}
and finally a concrete implementation:
class Foo extends SerializableModel {
//required by Constructable interface
ConstructorFunction constructor = () => new Foo();
//required by Serializable interface
String serialize() => "I'm a serialized string!";
Foo unserialize(String serializedString) {
Foo foo = new Foo();
//do unserialization work here to populate foo
return foo;
};
}
and now Foo (or anything that extends SerializableModel can be constructed with
Foo foo = new ModelFactory.fromSerializedString(Foo.constructor, serializedString);
The result of all this is that it enforces that every concrete class has a method which can create a new instance of itself from a serialized string, and there is also a common interface which allows that method to be called from a static context. It's still creating an extra object whose whole purpose is to switch from static to instance context, and then is thrown away, and there is a lot of other overhead as well, but at least all that ugliness is hidden from the user. Still, I'm not yet convinced that this is at all the best way to achieve this.
I suggest you define the unserialize function as named constructor like so:
abstract class Serializable<T> {
String serialize();
Serializable.unserialize(String serializedString);
}
This eliminates the need of static methods.
A possible implementation could look like this:
import 'dart:convert';
class JsonMap implements Serializable<JsonMap> {
Map map = {};
JsonMap() {
}
String serialize() {
return JSON.encode(map);
}
JsonMap.unserialize(String serializedString) {
this.map = JSON.decode(serializedString);
}
}
You can (de)serialize like so:
JsonMap m = new JsonMap();
m.map = { 'test': 1 };
print(m.serialize());
JsonMap n = new JsonMap.unserialize('{"hello": 1}');
print(n.map);
While testing this, I noticed that Dart will not throw any errors at you if you dont actually implement the methods that your class promises to implement with implements. This might just be a hicc-up with my local Dart, though.
I'm having a problem where the related table id fields return 'null' from my domain objects when using inheritance. Here is an example:
In /src/groovy/
BaseClass1.groovy
class BaseClass1 {
Long id
static mapping = {
tablePerConcreteClass true
}
}
BaseClass2.groovy
class BaseClass2 extends BaseClass1 {
String someOtherProperty
static constraints = {
someOtherProperty(maxSize:200)
}
static mapping = BaseClass1.mapping
}
In /grails-app/domain
ParentClass.groovy
class ParentClass extends BaseClass2 {
ChildClass myChild
static mapping = BaseClass2.mapping << {
version false
}
}
ChildClass.groovy
class ChildClass extends BaseClass1 {
String property
static mapping = BaseClass1.mapping
}
The problem appears here:
SomeotherCode.groovy
print parentClassInstance.myChild.id // returns the value
print parentClassInstance.myChildId // returns null
Any ideas what might be going on to get those dynamic properties to break like this?
After debugging into the get(AssociationName)Id source, I found the following:
The handler for this is:
GrailsDomainConfigurationUtil.getAssociationIdentifier(Object target, String propertyName,
GrailsDomainClass referencedDomainClass) {
String getterName = GrailsClassUtils.getGetterName(propertyName);
try {
Method m = target.getClass().getMethod(getterName, EMPTY_CLASS_ARRAY);
Object value = m.invoke(target);
if (value != null && referencedDomainClass != null) {
String identifierGetter = GrailsClassUtils.getGetterName(referencedDomainClass.getIdentifier().getName());
m = value.getClass().getDeclaredMethod(identifierGetter, EMPTY_CLASS_ARRAY);
return (Serializable)m.invoke(value);
}
}
catch (NoSuchMethodException e) {
// ignore
}
catch (IllegalAccessException e) {
// ignore
}
catch (InvocationTargetException e) {
// ignore
}
return null;
}
It threw an exception on the related class (value.getClass().getDeclaredMethod), saying NoSuchMethod for the method getId(). I was unable to remove the id declaration from the base class without Grails complaining that an identifier column was required. I tried marking id as public and it also complained that it wasn't there. So, I tried this
BaseClass {
Long id
public Long getId() { return this.#id }
}
and things worked on some classes, but not on others.
When I removed the ID declaration, I go an error: "Identity property not found, but required in domain class". On a whim, I tried adding #Entity to the concrete classes and viola! everything started working.
class BaseClass {
//Don't declare id!
}
#Entity
class ParentClass {}
#Entity
class ChildClass {}
I still think it is a grails bug that it needs to be added, but at least it is easy enough to work around.
I'm not sure why you are seeing this behavior, but I'm also not sure why you are doing some of the things you are doing here. Why have a domain class extend a POGO? Domains, Controllers, and Services are heavily managed by the Grails machinery, which probably was not designed for this sort of use. Specifically, I believe Grails builds the dynamic property getters for the GrailsDomainProperty(s) of GrailsDomainClass(es), not POGO's. In this case, you have an explicitly declared id field in BaseClass1 that is not a GrailsDomainProperty. I suspect that this POGO id property is not picked up by the Grails machinery that creates the dynamic property getters for Domains.
You might try putting BaseClass1/2 in /grails-app/domain, perhaps making them abstract if you don't want them instantiated, then extending them as you are and seeing if you observe the behavior you want.
I'm get null returned when attempting to access a subclass static variable through a overridden subclass accessor:
library resource;
abstract class Resource
{
String name;
String description;
Resource(this.name, this.description);
Resource.map(Map data)
{
...
_getDb()[this] = data;
}
abstract Map _getDb();
}
class Skill extends Resource
{
static Map _skills = {}
Skill.map(Map data) : super.map(data);
Map_getDb()
{
return _skills;
}
}
import 'resource.dart'
void main() {
useVMConfiguration();
test('constructor', () {
Skill skill = new Skill.map({
'name': 'foo'
});
}
}
Here I'm trying to call _getDb() on the (hopefully) now constructed subclass in the super constructor. Despite _skills being instantiated, _getDb() returns null.
Is this possible?
EDIT:
_skills is not present when inspecting this at _getDb():
this Skill [id=0]
description "bar" [id=19]
name "foo" [id=18]
Your example has several flaws as DartEditor shows.
Map_getDb() is missing a space between Map and _getDb().
Is this only in your question or in the code you run too?
abstract Map _getDb(); is also a syntax error.
In Dart a method is made abstract when you don't provide an implementation (; instead of {})
After this fixes the code works fine.