I have a piece of code, that moves an array depending on it's type. If the array is of TypeA objects, it will change TypeA. If it is TypeB it will change TypeB. The issue with the current code is the repeative blocks.
private function scrollRight():void
{
if (SELECTED == CONSTANT)
{
if (_avatarDataInstance.isFirstPage())
{
_buttons.enableLeftScroll();
}
setCurrentItems(_avatarDataInstance.getNextPage());
if (_avatarDataInstance.isLastPage())
{
_buttons.disableRightScroll();
}
}
if (SELECTED == DECOR)
{
if (_decorDataInstance.isFirstPage()) {
_buttons.enableLeftScroll();
}
setCurrentItems(_decorDataInstance.getNextPage());
if (_decorDataInstance.isLastPage()) {
_buttons.disableRightScroll();
}
}
}
This would be my idea code, where _selectedInstance is the instance of either TypeA or TypeB whichever is selected (TypeA and TypeB are classes).
private function scrollRight():void
{
if (_selectedInstance.isFirstPage())
{
_buttons.enableLeftScroll();
}
setCurrentItems(_selectedInstance.getNextPage());
if (_selectedInstance.isLastPage())
{
_buttons.disableRightScroll();
}
Any way, I can achieve this in actionscript? I have tried this :
_selectedInstance:Class;
if(somethingA)
selectedInstance(somethingA);
else
selectedInstance(somethingB);
Which stops working whenever I need to access any property (user) selectedInstance.testSomething();
You could create an interface or an abstract class , let's say TypeAbstract for instance , that TypeA and TypeB would extend ( or implement , depending on your choice ).
private function scrollRight():void
{
var instance:TypeAbstract;
switch( SELECTED )
{
case CONSTANT:
instance = _avatarDataInstance as TypeA;
break;
case DECOR:
instance = _decorDataInstance as TypeB;
break;
}
if(instance.isFirstPage() )
_buttons.enableLeftScroll();
setCurrentItems(instance.getNextPage());
if(instance.isLastPage() )
_buttons.disableRightScroll();
}
The general idea is to implement the common methods for TypeA & TypeB in the TypeAbstract class. Then you can override these methods in TypeA & TypeB to adapt the methods to the specifics of the subclass.
For more detailed information, check the links given by George Profenza.
Related
In my project, I have this special function that does needs to evaluate the following:
State -- represented by an enum -- and there are about 6 different states
Left Argument
Right Argument
Left and Right arguments are represented by strings, but their values can be the following:
"_" (a wildcard)
"1" (an integer string)
"abc" (a normal string)
So as you can see, to cover all every single possibility, there's about 2 * 3 * 6 = 36 different logics to evaluate and of course, using if-else in one giant function will not be feasible at all. I have encapsulated the above 3 input into an object that I'll pass to my function.
How would one try to use OOP to solve this. Would it make sense to have 6 different subclasses of the main State class with an evaluate() method, and then in their respective methods, I have if else statements to check:
if left & right arg are wildcards, do something
if left is number, right is string, do something else
Repeat for all the valid combinations in each State subclass
This feels like the right direction, but it also feels like theres alot of duplicate logic (for example check if both args are wildcards, or both strings etc.) for all 6 subclasses. Then my thought is to abstract it abit more and make another subclass:
For each state subclass, I have stateWithTwoWildCards, statewithTwoString etc.
But I feel like this is going way overboard and over-engineering and being "too" specific (I get that this technically adheres tightly to SOLID, especially SRP and OCP concepts). Any thoughts on this?
Possibly something like template method pattern can be useful in this case. I.e. you will encapsulate all the checking logic in the base State.evaluate method and create several methods which subclasses will override. Something along this lines:
class StateBase
def evaluate():
if(bothWildcards)
evalBothWildcards()
else if(bothStrings)
evalBothStrings()
else if ...
def evalBothWildcards():
...
def evalBothStrings():
...
Where evalBothWildcards, evalBothStrings, etc. will be overloaded in inheritors.
there's about 2 * 3 * 6 = 36 different logics to evaluate
We can apply divide and conquer technique.
you have 6 states. It is possible to use Chain of Responibility pattern here to choose appropriate state handler
when desired state handler is found, then we can apply desired function. The appropriate function can be considered as strategy. So it is a place where Strategy pattern can be applied.
we can separate strategies by appropriate states and put them in simple factory to get desired strategy by key.
This is what we will do. So let's see it more thoroughly.
Chain of responsibility pattern
If you have a lot if else statements, it is possible to use Chain of Responsibility pattern. As wiki says about Chain of Responsibility:
The chain-of-responsibility pattern is a behavioral design pattern
consisting of a source of command objects and a series of processing
objects. Each processing object contains logic that defines the
types of command objects that it can handle; the rest are passed to
the next processing object in the chain. A mechanism also exists for
adding new processing objects to the end of this chain
So let's dive in code. Let me show an example via C#.
So this is our Argument class which has Left and Right operands:
public class Arguments
{
public string Left { get; private set; }
public string Right { get; private set; }
public MyState MyState { get; private set; }
public MyKey MyKey => new MyKey(MyState, Left);
public Arguments(string left, string right, MyState myState)
{
Left = left;
Right = right;
MyState = myState;
}
}
And this is your 6 states:
public enum MyState
{
One, Two, Three, Four, Five, Six
}
This is start of Decorator pattern. This is an abstraction of StateHandler which defines behaviour to to set next handler:
public abstract class StateHandler
{
public abstract MyState State { get; }
private StateHandler _nextStateHandler;
public void SetSuccessor(StateHandler nextStateHandler)
{
_nextStateHandler = nextStateHandler;
}
public virtual IDifferentLogicStrategy Execute(Arguments arguments)
{
if (_nextStateHandler != null)
return _nextStateHandler.Execute(arguments);
return null;
}
}
and its concrete implementations of StateHandler:
public class OneStateHandler : StateHandler
{
public override MyState State => MyState.One;
public override IDifferentLogicStrategy Execute(Arguments arguments)
{
if (arguments.MyState == State)
return new StrategyStateFactory().GetInstanceByMyKey(arguments.MyKey);
return base.Execute(arguments);
}
}
public class TwoStateHandler : StateHandler
{
public override MyState State => MyState.Two;
public override IDifferentLogicStrategy Execute(Arguments arguments)
{
if (arguments.MyState == State)
return new StrategyStateFactory().GetInstanceByMyKey(arguments.MyKey);
return base.Execute(arguments);
}
}
and the third state handler looks like this:
public class ThreeStateHandler : StateHandler
{
public override MyState State => MyState.Three;
public override IDifferentLogicStrategy Execute(Arguments arguments)
{
if (arguments.MyState == State)
return new StrategyStateFactory().GetInstanceByMyKey(arguments.MyKey);
return base.Execute(arguments);
}
}
Strategy pattern
Let's pay attention to the following row of code:
return new StrategyStateFactory().GetInstanceByMyKey(arguments.MyKey);
The above code is an example of using Strategy pattern. We have different ways or strategies to handle
your cases. Let me show a code of strategies of evaluation of your expressions.
This is an abstraction of strategy:
public interface IDifferentLogicStrategy
{
string Evaluate(Arguments arguments);
}
And its concrete implementations:
public class StrategyWildCardStateOne : IDifferentLogicStrategy
{
public string Evaluate(Arguments arguments)
{
// your logic here to evaluate "_" (a wildcard)
return "StrategyWildCardStateOne";
}
}
public class StrategyIntegerStringStateOne : IDifferentLogicStrategy
{
public string Evaluate(Arguments arguments)
{
// your logic here to evaluate "1" (an integer string)
return "StrategyIntegerStringStateOne";
}
}
And the third strategy:
public class StrategyNormalStringStateOne : IDifferentLogicStrategy
{
public string Evaluate(Arguments arguments)
{
// your logic here to evaluate "abc" (a normal string)
return "StrategyNormalStringStateOne";
}
}
Simple factory
There is no pattern like simple factory. However, it is a place where we can get instances of strategies by key. So by doing this we avoided to use multiple if else statements to choose correct strategy.
So, we need a place where we can store strategies by state and argument value. At first, let's create MyKey struct. It will have help us to differentiate State and arguments:
public struct MyKey
{
public readonly MyState MyState { get; }
public readonly string ArgumentValue { get; } // your three cases: "_",
// an integer string, a normal string
public MyKey(MyState myState, string argumentValue)
{
MyState = myState;
ArgumentValue = argumentValue;
}
public override bool Equals([NotNullWhen(true)] object? obj)
{
return obj is MyKey mys
&& mys.MyState == MyState
&& mys.ArgumentValue == ArgumentValue;
}
public override int GetHashCode()
{
unchecked // Overflow is fine, just wrap
{
int hash = 17;
hash = hash * 23 + MyState.GetHashCode();
hash = hash * 23 + ArgumentValue.GetHashCode();
return hash;
}
}
}
and then we can create a simple factory:
public class StrategyStateFactory
{
private Dictionary<MyKey, IDifferentLogicStrategy>
_differentLogicStrategyByStateAndValue =
new Dictionary<MyKey, IDifferentLogicStrategy>()
{
{ new MyKey(MyState.One, "_"), new StrategyWildCardStateOne() },
{ new MyKey(MyState.One, "intString"),
new StrategyIntegerStringStateOne() },
{ new MyKey(MyState.One, "normalString"),
new StrategyNormalStringStateOne() }
};
public IDifferentLogicStrategy GetInstanceByMyKey(MyKey myKey)
{
return _differentLogicStrategyByStateAndValue[myKey];
}
}
So we've written our strategies and we've stored these strategies in simple factory StrategyStateFactory.
Then we need to check the above implementation:
StateHandler chain = new OneStateHandler();
StateHandler secondStateHandler = new TwoStateHandler();
StateHandler thirdStateHandler = new ThreeStateHandler();
chain.SetSuccessor(secondStateHandler);
secondStateHandler.SetSuccessor(thirdStateHandler);
Arguments arguments = new Arguments("_", "_", MyState.One);
IDifferentLogicStrategy differentLogicStrategy = chain.Execute(arguments);
string evaluatedResult =
differentLogicStrategy.Evaluate(arguments); // output: "StrategyWildCardStateOne"
I believe I gave basic idea how it can be done.
I am trying to clean and refactor my service code which currently looks like this-
public void generateBalance(Receipt receipt) {
if (receipt.getType().equals(X) && receipt.getRegion.equals(EMEA)) {
// do something to the receipt that's passed
} else if (receiptType.equals(Y)) {
// do something to the receipt
} else if (receipt.getRegion.equals(APAC) {
// call an external API and update the receipt
}....
...
// finally
dataStore.save(receipt);
Basically there's a bunch of conditionals that are in this main service which look for certain fields in the object that is being passed. Either it's the type or the region.
I was looking to use this design pattern- https://www.refactoring.com/catalog/replaceConditionalWithPolymorphism.html
However, I am not sure how this would work for a service class. Currently my REST handler calls this particular service. Also how can I do polymorphism for both the "receiptType" and "region"?
Is there a way I can just do all the updates to the receipt once in different services, then finally save the receipt at one location? (maybe a base class?) I am really confused on how to start. TIA!
If your classes should have the same behaviour, then it becomes pretty simple to use polymorpism. The pattern is called as Strategy. Let me show an example.
At first we need to use enum. If you do not have enum, then you can create a method which will return enum value based on your conditions:
if (receipt.getType().equals(X) && receipt.getRegion.equals(EMEA)) // other
// code is omitted for the brevity
So enum will look like this:
public enum ReceiptType
{
Emea, Y, Apac
}
Then we need an abstract class which will describe behaviour for derived classes:
public abstract class ActionReceipt
{
public abstract string Do();
}
And our derived classes will look this:
public class ActionReceiptEmea : ActionReceipt
{
public override string Do()
{
return "I am Emea";
}
}
public class ActionReceiptY : ActionReceipt
{
public override string Do()
{
return "I am Y";
}
}
public class ActionReceiptApac : ActionReceipt
{
public override string Do()
{
return "I am Apac";
}
}
Moreover, we need a factory which will create derived classes based on enum. So we can use Factory pattern with a slight modification:
public class ActionReceiptFactory
{
private Dictionary<ReceiptType, ActionReceipt> _actionReceiptByType =
new Dictionary<ReceiptType, ActionReceipt>
{
{
ReceiptType.Apac, new ActionReceiptApac()
},
{
ReceiptType.Emea, new ActionReceiptEmea()
},
{
ReceiptType.Y, new ActionReceiptY()
}
};
public ActionReceipt GetInstanceByReceiptType(ReceiptType receiptType) =>
_actionReceiptByType[receiptType];
}
And then polymorpism in action will look like this:
void DoSomething(ReceiptType receiptType)
{
ActionReceiptFactory actionReceiptFactory = new ActionReceiptFactory();
ActionReceipt receipt =
actionReceiptFactory.GetInstanceByReceiptType(receiptType);
string someDoing = receipt.Do(); // Output: "I am Emea"
}
UPDATE:
You can create some helper method which will return enum value based on
your logic of region and receiptType:
public class ReceiptTypeHelper
{
public ReceiptType Get(ActionReceipt actionReceipt)
{
if (actionReceipt.GetType().Equals("Emea"))
return ReceiptType.Emea;
else if (actionReceipt.GetType().Equals("Y"))
return ReceiptType.Y;
return ReceiptType.Apac;
}
}
and you can call it like this:
void DoSomething()
{
ReceiptTypeHelper receiptTypeHelper = new ReceiptTypeHelper();
ReceiptType receiptType = receiptTypeHelper
.Get(new ActionReceiptEmea());
ActionReceiptFactory actionReceiptFactory = new
ActionReceiptFactory();
ActionReceipt receipt =
actionReceiptFactory.GetInstanceByReceiptType(receiptType);
string someDoing = receipt.Do(); // Output: "I am Emea"
}
I've been dabbling in Dlang recently as C++ just wasn't quite sitting right with me after having used Python for so long. While dabbling, I came across what I thought would be a very simple exercise in polymorphism. I suppose how you would expect something to work and what it actually does are two entirely different things for reasons an end user probably can't comprehend. That being said, here is the source code of my "sandbox.D":
import std.stdio;
class Animal {
string voice = "--silence--";
void speak() {
writeln(this.voice);
}
}
class Dog : Animal {
string voice = "Whoof!";
}
int main() {
auto a = new Animal();
auto d = new Dog();
writeln(a.voice); // Prints "--silence--"
writeln(d.voice); // Prints "Whoof!"
a.speak(); // Prints "--silence--"
d.speak(); // Prints "--silence--" NOT "Whoof!"
return 0;
}
I guess my issue is why the "this" keyword just doesn't seem to be functioning how you would expect it to in the C++ successor language.
Methods are polymorphic, variables aren't. So instead of making the voice a variable, you want to override speak in the child.
Also, the auto return type doesn't work with polymorphism, you need to actually specify the types. (The reason is that auto return makes a function template in the compiler, which in theory could have multiple overridable slots in the function table, so it just doesn't try to put it in.)
So try this out:
import std.stdio;
class Animal {
void speak() { // changed to void instead of auto
writeln("--silence--");
}
}
class Dog : Animal {
override void speak() { // the override tells it to override the base method
writeln("woof");
}
}
int main() {
auto d = new Dog();
d.speak();
return 0;
}
If you have a lot of shared functionality and want to reuse one function with slight changes in child classes, you might make a method instead of a variable that just returns something.
Like string voice() { return "woof"; }, then it can be overridden in children.
Another way is to use template this parameter:
import std.stdio;
class Animal {
string voice;
void speak(this C)() {
writeln((cast(C)this).voice);
}
}
class Dog : Animal {
string voice = "Whoof!";
}
int main() {
auto a = new Animal();
auto d = new Dog();
a.speak(); // Prints ""
d.speak(); // Prints "Whoof!"
return 0;
}
Or when you do not need to have voice as a member:
import std.stdio;
class Animal {
static immutable voice = "";
void speak(this C)() {
writeln(C.voice);
}
}
class Dog : Animal {
static immutable voice = "Whoof!";
}
int main() {
auto a = new Animal();
auto d = new Dog();
a.speak(); // Prints ""
d.speak(); // Prints "Whoof!"
return 0;
}
I have a constructor such as:
public AnalyticsController(ClassA classA, ClassB classB, bool isLiveEnvironment)
{
...
}
isLiveEnvironment is determined using a call to an existing static class such as:
MultiTenancyDetection.GetInstance().IsLive();
I would like to be able to make this call outside of the controller and inject the result into isLiveEnvironment. Is this possible? I can not see how this can be done.
You can accomplish this using WithConstructorArgument and using a callback:
kernel.Bind<AnalyticsController>()
.ToSelf()
.WithConstructorArgument("isLiveEnvironment", ctx => MultiTenancyDetection.GetInstance().IsLive() );
You can even achieve this more generally (but i would not really recommend binding such a generic type for such a specific use case):
IBindingRoot.Bind<bool>().ToMethod(x => MultiTenancyDetection.GetInstance().IsLive())
.When(x => x.Target.Name == "isLiveEnvironment");
Alternatively, if you need the same configuration value in several / a lot of classes, create an interface for it:
public interface IEnvironment
{
bool IsLive { get; }
}
internal class Environment : IEnvironment
{
public bool IsLive
{
get
{
return MultiTenancyDetection.GetInstance().IsLive();
}
}
}
IBindingRoot.Bind<IEnvironment>().To<Environment>();
How can I bind InitializerForXXX (non-generic implementation) to IInitializer<XXX> (generic interface) using Ninject Conventions so that requests for an IInitializer<T> resolve a non-generic implementation whose name starts with InitializerFor and end with typeof(T).Name like:
initializerFactory.CreateFor<Blue>(); //resolves InitializerOfBlue
initializerFactory.CreateFor<ShadeOfBlue>(); //resolves InitializerOfShadeOfBlue
where no non-abstract class directly implement IInitializer<T>, and some implementations inherit from other implementations:
InitializerForShadeOfBlue inherits from InitializerForBlue
InitializerForBlue inherits from abstract Initializer<Blue>
abstract Initializer<T> directly implements IInitializer<T>
I'm hoping I can use a .EndsWith(typeof(T).Name) for a given IInitializer<T> convention I can use, because there are literally hundreds of initializers in the ShadeOfxxx vein. If I have to map all of them, I'm better off finding a way to resolve with reflection at runtime.
Given the following:
UPDATE: bindings with custom binding generator (see my answer below for implementation)
void Bootstrap(IBindingRoot kernel)
{
kernel.Bind<IInitializerFactory>()
.To<InitializerFactory>()
.InSingletonScope();
kernel.Bind(scanner =>
scanner.FromThisAssembly().SelectAllClasses()
.WhichAreNotGeneric()
.InheritedFrom(typeof(IComplexContent))
.BindAllInterfaces());
kernel.Bind(scanner =>
scanner.FromThisAssembly().SelectAllClasses()
.WhichAreNotGeneric()
.InheritedFrom(typeof(IInitializer<>))
.BindWith<FirstTypeParameterNameMatchesEndOfBoundClassNameGenerator>());
}
main method
void Main(IEnumerable<string> values)
{
// setup bindings
var kernel = new StandardKernel();
Bootstrap(kernel);
IInitializerFactory initializerFactory =
kernel.Get<IInitializerFactory>();
IInitializer<ShadeOfBlueComplexContent> initializer =
initializerFactory.CreateFor<ShadeOfBlueComplexContent>();
initializer.Initialize(values);
}
initializer factory
interface IInitializerFactory
{
IInitializer<T> CreateFor<T>() where T : class, IComplexContent, new();
}
class InitializerFactory : IInitializerFactory
{
public IInitializer<T> CreateFor<T>() where T : class, IComplexContent, new()
{
return MagicallyGetInitializer<T>();
}
//behind the curtain, whirring noises are heard as 't' is resolved...
private static IInitializer<T> MagicallyGetInitializer<T>()
where T : class, IComplexContent, new()
{
IInitializer<T> i = null;
return i;
}
}
initializers
interface IInitializer<out T> where T : IComplexContent
{
T Initialize(IEnumerable<string> values);
}
abstract class Initializer<T> : IInitializer<T> where T : IComplexContent
{
public abstract T Initialize(IEnumerable<string> values);
}
class InitializerOfBlue : Initializer<Blue>
{
private readonly Blue _content;
public InitializerOfBlue(Blue content) {_content = content;}
public override Blue Initialize(IEnumerable<string> values)
{
_content.BlueSpecificProperty = values.ElementAt(0);
//... populate other blue-specific properties like this
return _content;
}
}
class InitializerOfShadeOfBlue : InitializerOfBlue
{
public InitializerOfShadeOfBlue(ShadeOfBlue content) : base(content){}
}
content models
interface IComplexContent
{
string OneBasicProperty { get; set; }
// other properties are specific to implementation
string UniqueOperation();
}
abstract class BaseComplexContent : IComplexContent
{
public string OneBasicProperty { get; set; }
public abstract string UniqueOperation();
}
class Blue : BaseComplexContent
{
// initializer sets this
public string PropertyForAllKindsOfBlue { get; set; }
// initializer doesn't interact with this
public override string UniqueOperation() {return "I'm plain.";}
}
class ShadeOfBlue : Blue
{
// initializer doesn't interact with this
public override string UniqueOperation() {return "I'm fabulous!";}
}
You are over specifying the class selection
kernel.Bind(scanner =>
scanner.FromThisAssembly().SelectAllClasses()
.WhichAreNotGeneric()
.InheritedFrom(typeof (IInitializer<>))
This is already enough. What you need to do though is to add a custom Binding Generator. That selects IInitializer<Blue> for InitializerForBlue and IInitializer<ShadeOfBlue> for InitializerForShadeOfBlue
https://github.com/ninject/ninject.extensions.conventions/wiki/Projecting-Services-to-Bind
BEGIN SOLUTION CANDIDATE - custom binding generator:
custom binding generator
Thanks for the advice, #RemoGloor and #RubenBartelink. I'm stumped though - the problem is that I wind up binding the IInitializer<Blue> to InitializerOfShadeOfBlue. I need to be able to somehow change the generic type argument from Blue to ShadeOfBlue in the IInitializer<Blue> binding candidate, since IInitializer<ShadeOfBlue> is what will be requested from the factory method at runtime.
Is there a way to modify the generic type argument list of the binding candidate? Or am I barking up the wrong implementation? Any edit suggestions to my OP or this answer are appreciated.
/// <summary>Creates bindings on open generic types where bound implementations'
/// names end with the name of the generic type argument</summary>
public class FirstTypeParameterNameMatchesEndOfBoundClassNameGenerator : IBindingGenerator
{
public IEnumerable<IBindingWhenInNamedWithOrOnSyntax<object>> CreateBindings(Type type, IBindingRoot bindingRoot)
{
if (type == null) throw new ArgumentNullException("type");
if (bindingRoot == null) throw new ArgumentNullException("bindingRoot");
// only consider concrete, non-abstract classes
if (type.IsInterface || type.IsAbstract) yield break;
var bindingType = GetBindingType(type);
if (bindingType != null)
yield return bindingRoot.Bind(bindingType).To(type);
// ARGH! bindingType == IInitializer`1[[Blue]] but I want
// IInitializer`1[[ShadeOfBlue]] for type == ShadeOfBlue
}
private static Type GetBindingType(Type type)
{
Type goodMatch = null;
foreach (var candidate in type.GetInterfaces())
{
// skip non-generic interfaces
if (!candidate.IsGenericType) continue;
// assumption: using argument in first position
var firstArg = candidate.GetGenericArguments().First();
if (!type.Name.EndsWith(firstArg.Name)) continue;
// IInitializer<XXX> matches InitializerOfXXX
goodMatch = candidate;
break;
}
if (goodMatch == null)
{
// if no match on interfaces, walk through the ancestor types
foreach (var candidate in type.GetAllAncestors())
{
goodMatch = GetBindingType(candidate);
if (goodMatch != null) break;
}
}
return goodMatch;
}
Type Extension helper
public static class TypeExtensions
{
// returns all ancestor types starting with the parent
public static IEnumerable<Type> GetAllAncestors(this Type type)
{
for (var current = type.BaseType; current != null; current = current.BaseType)
yield return current;
}
}
END SOLUTION CANDIDATE - custom binding generator