I'm looking for a way to reduce the boilerplate code of my NodeJS backend. In Lombok there is e.g. the possibility to inject constructors and getter/setter by annotation for objects.
Is there a way to do this in TypeScript?
I googled it quickly and found projects like this which attempt to bring Lombok-like capabilities to TypeScript, but as you can see, those project are scarce and not that widely used. That implies a question: Why would you want a tool like that?
TS is already pretty good in reducing boilerplate. When I define a class, I usually do it like this:
class A {
constructor(private fieldA: string, private readonly fieldB = 0) {}
}
This is quite concise, isn't it? I guess you are comparing capabilities of TS to those of Java. Java is very wordy and Lombok helps with that greatly. But TS and JS are different, and while some problems, which Lombok solves, are solved by TS already, others are not an issue in the world of TS and JS.
First of all, the syntax above creates class fields of certain types, with access modifiers and you can also spot the readonly keyword in front of fieldB and its default value 0. On top of that, those are created together with a constructor, which implicitly assigns values to instance fields upon execution (see, there is no this.fieldA = fieldA). So this already more than covers the Lombok's capability to inject constructors. Note on this: In JS (and therefore in TS), you can have only single constructor. JS doesn't support method overloading.
Now about the getters/setters, those are not used the same way in JS (or TS) as they are in Java. In JS, it is a norm that you are working with fields directly, and the setters and getters are used only in special cases where you want to:
Forbid setting a value to an object's property in runtime by defining only a getter. Now this is usually a bit of an overkill, and since you use TS, you can just declare the field as readonly and compiler will make sure you don't assign to that property - no need to use a getter. If you develop in JS without compile time checks, the convention is to mark properties that are private (those you definitely shouldn't modify) with underscore. Either way, it can still happen that you modify a variable that you aren't supposed to modify, but unlike in Java, this is not deemed a reason good enough to use get/set everywhere in JS (and TS). Instead, if you really need to be certain that no modifications happen in runtime, you either use the aforementioned getter without setter, or you configure the object's property as non-writable.
Having a custom logic in set/get functions is the other good reason to employ them. A common use case for this is a getter that is computed out of multiple variables but you still want it to look like an field on an object. That's because in JS, when you invoke a getter, you don't actually use () after the getter name. Now because this logic is custom, it can't be generated just by using an annotation.
So as you can see, some problems Lombok deals with in Java are already dealt with in TS and others are non-issues.
Edit 5-9-2021 - answer to #Reijo's question:
Lomboks functionality goes beyond getters/setters/constructors. Looking at the #Builder Annotation, I am interested in what you would say about this.
If the question is just about whether there is a TypeScript/JavaScript library that offers more or less the same collection of utilities as Lombok for Java, to my knowledge the answer is NO. I think partly it is due to capabilities that TypeScript provides out of the box (as I already outlined above), which brings me back to the point that Java needs Lombok more than languages like TypeScript or Groovy do. When you need something that TS doesn't provide, like the builder pattern, you can use libraries solving a particular problem, like builder-pattern (using JS Proxy in its core) or thanks to the flexible nature of JS (and in effect TS) write it on your own easily.
That's all nice, but you'd perhaps like to add functionality in more declarative way - via annotations (in TS world those are called decorators and they work differently), as Lombok does it. This might prove complex.
First of all, if you modify the type via decorator in TS, TS compiler doesn't recognize the change. So if you augment class by, let's say, adding a method to it in your decorator, TS won't recognize that new method. See this discussion for details.
This means that you either give up on decorators and use functions instead to modify the type (which you can), or you dive into AST. That's btw how Lombok works. It takes annotated types in a compilation phase called annotation processing and thanks to a hack in javac (and Eclipse compiler) modifies their AST (to eg. create an inner builder for given class). One could do it in a somewhat similar way with TS/JS.
Though there is nothing like annotations processing in TS nor JS as such, you could still create a build step that takes a source code and modifies it's AST to achieve your goals (which is how Babel works too). This might result in adding a method to a class, generating a builder etc. based on an annotation (in a broad sense - not necessarily a decorator) used.
This approach is a challenge though. Besides AST being an advanced topic, even if you get it working, you'd need support from your IDE, which nowadays also means support from language servers. And that's not for the faint of heart.
However, my edit is not supposed to scare anyone away if you plan to create something like Lombok for TS, since it seems quite some people would like to see it in TS/JS world. It should only show you what lies ahead ;).
I found an alternative to #Getters and #Setters Lombok decorators.
Try this :
import { capitalize } from "lodash";
const Getters = () => <T extends {new(...args:any[]):{}}>(constructor:T) => {
return class extends constructor {
constructor(...args: any[]) {
super(...args);
const props = Reflect.ownKeys(this);
props.forEach((prop: string) => {
const capitalizedKey = capitalize(prop);
const methodName = `get${capitalizedKey}`;
Object.defineProperty(this, methodName, { value: () => this[prop] });
});
}
}
}
const Setters = () => <T extends {new(...args:any[]):{}}>(constructor:T) => {
return class extends constructor {
constructor(...args: any[]) {
super(...args);
const props = Reflect.ownKeys(this);
props.forEach((prop: string) => {
const capitalizedKey = capitalize(prop);
const methodName = `set${capitalizedKey}`;
Object.defineProperty(this, methodName, { value: (newValue: any) => { this[prop] = newValue } });
});
}
}
}
#Getters()
#Setters()
export class Person {
[x: string]: any;
nom: string;
prenom: string;
constructor(nom: string, prenom: string) {
this.nom = nom;
this.prenom = prenom;
}
}
What's the advantage of using getters and setters - that only get and set - instead of simply using public fields for those variables?
If getters and setters are ever doing more than just the simple get/set, I can figure this one out very quickly, but I'm not 100% clear on how:
public String foo;
is any worse than:
private String foo;
public void setFoo(String foo) { this.foo = foo; }
public String getFoo() { return foo; }
Whereas the former takes a lot less boilerplate code.
There are actually many good reasons to consider using accessors rather than directly exposing fields of a class - beyond just the argument of encapsulation and making future changes easier.
Here are the some of the reasons I am aware of:
Encapsulation of behavior associated with getting or setting the property - this allows additional functionality (like validation) to be added more easily later.
Hiding the internal representation of the property while exposing a property using an alternative representation.
Insulating your public interface from change - allowing the public interface to remain constant while the implementation changes without affecting existing consumers.
Controlling the lifetime and memory management (disposal) semantics of the property - particularly important in non-managed memory environments (like C++ or Objective-C).
Providing a debugging interception point for when a property changes at runtime - debugging when and where a property changed to a particular value can be quite difficult without this in some languages.
Improved interoperability with libraries that are designed to operate against property getter/setters - Mocking, Serialization, and WPF come to mind.
Allowing inheritors to change the semantics of how the property behaves and is exposed by overriding the getter/setter methods.
Allowing the getter/setter to be passed around as lambda expressions rather than values.
Getters and setters can allow different access levels - for example the get may be public, but the set could be protected.
Because 2 weeks (months, years) from now when you realize that your setter needs to do more than just set the value, you'll also realize that the property has been used directly in 238 other classes :-)
A public field is not worse than a getter/setter pair that does nothing except returning the field and assigning to it. First, it's clear that (in most languages) there is no functional difference. Any difference must be in other factors, like maintainability or readability.
An oft-mentioned advantage of getter/setter pairs, isn't. There's this claim that you can change the implementation and your clients don't have to be recompiled. Supposedly, setters let you add functionality like validation later on and your clients don't even need to know about it. However, adding validation to a setter is a change to its preconditions, a violation of the previous contract, which was, quite simply, "you can put anything in here, and you can get that same thing later from the getter".
So, now that you broke the contract, changing every file in the codebase is something you should want to do, not avoid. If you avoid it you're making the assumption that all the code assumed the contract for those methods was different.
If that should not have been the contract, then the interface was allowing clients to put the object in invalid states. That's the exact opposite of encapsulation If that field could not really be set to anything from the start, why wasn't the validation there from the start?
This same argument applies to other supposed advantages of these pass-through getter/setter pairs: if you later decide to change the value being set, you're breaking the contract. If you override the default functionality in a derived class, in a way beyond a few harmless modifications (like logging or other non-observable behaviour), you're breaking the contract of the base class. That is a violation of the Liskov Substitutability Principle, which is seen as one of the tenets of OO.
If a class has these dumb getters and setters for every field, then it is a class that has no invariants whatsoever, no contract. Is that really object-oriented design? If all the class has is those getters and setters, it's just a dumb data holder, and dumb data holders should look like dumb data holders:
class Foo {
public:
int DaysLeft;
int ContestantNumber;
};
Adding pass-through getter/setter pairs to such a class adds no value. Other classes should provide meaningful operations, not just operations that fields already provide. That's how you can define and maintain useful invariants.
Client: "What can I do with an object of this class?"
Designer: "You can read and write several variables."
Client: "Oh... cool, I guess?"
There are reasons to use getters and setters, but if those reasons don't exist, making getter/setter pairs in the name of false encapsulation gods is not a good thing. Valid reasons to make getters or setters include the things often mentioned as the potential changes you can make later, like validation or different internal representations. Or maybe the value should be readable by clients but not writable (for example, reading the size of a dictionary), so a simple getter is a nice choice. But those reasons should be there when you make the choice, and not just as a potential thing you may want later. This is an instance of YAGNI (You Ain't Gonna Need It).
Lots of people talk about the advantages of getters and setters but I want to play devil's advocate. Right now I'm debugging a very large program where the programmers decided to make everything getters and setters. That might seem nice, but its a reverse-engineering nightmare.
Say you're looking through hundreds of lines of code and you come across this:
person.name = "Joe";
It's a beautifully simply piece of code until you realize its a setter. Now, you follow that setter and find that it also sets person.firstName, person.lastName, person.isHuman, person.hasReallyCommonFirstName, and calls person.update(), which sends a query out to the database, etc. Oh, that's where your memory leak was occurring.
Understanding a local piece of code at first glance is an important property of good readability that getters and setters tend to break. That is why I try to avoid them when I can, and minimize what they do when I use them.
In a pure object-oriented world getters and setters is a terrible anti-pattern. Read this article: Getters/Setters. Evil. Period. In a nutshell, they encourage programmers to think about objects as of data structures, and this type of thinking is pure procedural (like in COBOL or C). In an object-oriented language there are no data structures, but only objects that expose behavior (not attributes/properties!)
You may find more about them in Section 3.5 of Elegant Objects (my book about object-oriented programming).
There are many reasons. My favorite one is when you need to change the behavior or regulate what you can set on a variable. For instance, lets say you had a setSpeed(int speed) method. But you want that you can only set a maximum speed of 100. You would do something like:
public void setSpeed(int speed) {
if ( speed > 100 ) {
this.speed = 100;
} else {
this.speed = speed;
}
}
Now what if EVERYWHERE in your code you were using the public field and then you realized you need the above requirement? Have fun hunting down every usage of the public field instead of just modifying your setter.
My 2 cents :)
One advantage of accessors and mutators is that you can perform validation.
For example, if foo was public, I could easily set it to null and then someone else could try to call a method on the object. But it's not there anymore! With a setFoo method, I could ensure that foo was never set to null.
Accessors and mutators also allow for encapsulation - if you aren't supposed to see the value once its set (perhaps it's set in the constructor and then used by methods, but never supposed to be changed), it will never been seen by anyone. But if you can allow other classes to see or change it, you can provide the proper accessor and/or mutator.
Thanks, that really clarified my thinking. Now here is (almost) 10 (almost) good reasons NOT to use getters and setters:
When you realize you need to do more than just set and get the value, you can just make the field private, which will instantly tell you where you've directly accessed it.
Any validation you perform in there can only be context free, which validation rarely is in practice.
You can change the value being set - this is an absolute nightmare when the caller passes you a value that they [shock horror] want you to store AS IS.
You can hide the internal representation - fantastic, so you're making sure that all these operations are symmetrical right?
You've insulated your public interface from changes under the sheets - if you were designing an interface and weren't sure whether direct access to something was OK, then you should have kept designing.
Some libraries expect this, but not many - reflection, serialization, mock objects all work just fine with public fields.
Inheriting this class, you can override default functionality - in other words you can REALLY confuse callers by not only hiding the implementation but making it inconsistent.
The last three I'm just leaving (N/A or D/C)...
Depends on your language. You've tagged this "object-oriented" rather than "Java", so I'd like to point out that ChssPly76's answer is language-dependent. In Python, for instance, there is no reason to use getters and setters. If you need to change the behavior, you can use a property, which wraps a getter and setter around basic attribute access. Something like this:
class Simple(object):
def _get_value(self):
return self._value -1
def _set_value(self, new_value):
self._value = new_value + 1
def _del_value(self):
self.old_values.append(self._value)
del self._value
value = property(_get_value, _set_value, _del_value)
Well i just want to add that even if sometimes they are necessary for the encapsulation and security of your variables/objects, if we want to code a real Object Oriented Program, then we need to STOP OVERUSING THE ACCESSORS, cause sometimes we depend a lot on them when is not really necessary and that makes almost the same as if we put the variables public.
EDIT: I answered this question because there are a bunch of people learning programming asking this, and most of the answers are very technically competent, but they're not as easy to understand if you're a newbie. We were all newbies, so I thought I'd try my hand at a more newbie friendly answer.
The two main ones are polymorphism, and validation. Even if it's just a stupid data structure.
Let's say we have this simple class:
public class Bottle {
public int amountOfWaterMl;
public int capacityMl;
}
A very simple class that holds how much liquid is in it, and what its capacity is (in milliliters).
What happens when I do:
Bottle bot = new Bottle();
bot.amountOfWaterMl = 1500;
bot.capacityMl = 1000;
Well, you wouldn't expect that to work, right?
You want there to be some kind of sanity check. And worse, what if I never specified the maximum capacity? Oh dear, we have a problem.
But there's another problem too. What if bottles were just one type of container? What if we had several containers, all with capacities and amounts of liquid filled? If we could just make an interface, we could let the rest of our program accept that interface, and bottles, jerrycans and all sorts of stuff would just work interchangably. Wouldn't that be better? Since interfaces demand methods, this is also a good thing.
We'd end up with something like:
public interface LiquidContainer {
public int getAmountMl();
public void setAmountMl(int amountMl);
public int getCapacityMl();
}
Great! And now we just change Bottle to this:
public class Bottle implements LiquidContainer {
private int capacityMl;
private int amountFilledMl;
public Bottle(int capacityMl, int amountFilledMl) {
this.capacityMl = capacityMl;
this.amountFilledMl = amountFilledMl;
checkNotOverFlow();
}
public int getAmountMl() {
return amountFilledMl;
}
public void setAmountMl(int amountMl) {
this.amountFilled = amountMl;
checkNotOverFlow();
}
public int getCapacityMl() {
return capacityMl;
}
private void checkNotOverFlow() {
if(amountOfWaterMl > capacityMl) {
throw new BottleOverflowException();
}
}
I'll leave the definition of the BottleOverflowException as an exercise to the reader.
Now notice how much more robust this is. We can deal with any type of container in our code now by accepting LiquidContainer instead of Bottle. And how these bottles deal with this sort of stuff can all differ. You can have bottles that write their state to disk when it changes, or bottles that save on SQL databases or GNU knows what else.
And all these can have different ways to handle various whoopsies. The Bottle just checks and if it's overflowing it throws a RuntimeException. But that might be the wrong thing to do.
(There is a useful discussion to be had about error handling, but I'm keeping it very simple here on purpose. People in comments will likely point out the flaws of this simplistic approach. ;) )
And yes, it seems like we go from a very simple idea to getting much better answers quickly.
Please note also that you can't change the capacity of a bottle. It's now set in stone. You could do this with an int by declaring it final. But if this was a list, you could empty it, add new things to it, and so on. You can't limit the access to touching the innards.
There's also the third thing that not everyone has addressed: getters and setters use method calls. That means that they look like normal methods everywhere else does. Instead of having weird specific syntax for DTOs and stuff, you have the same thing everywhere.
I know it's a bit late, but I think there are some people who are interested in performance.
I've done a little performance test. I wrote a class "NumberHolder" which, well, holds an Integer. You can either read that Integer by using the getter method
anInstance.getNumber() or by directly accessing the number by using anInstance.number. My programm reads the number 1,000,000,000 times, via both ways. That process is repeated five times and the time is printed. I've got the following result:
Time 1: 953ms, Time 2: 741ms
Time 1: 655ms, Time 2: 743ms
Time 1: 656ms, Time 2: 634ms
Time 1: 637ms, Time 2: 629ms
Time 1: 633ms, Time 2: 625ms
(Time 1 is the direct way, Time 2 is the getter)
You see, the getter is (almost) always a bit faster. Then I tried with different numbers of cycles. Instead of 1 million, I used 10 million and 0.1 million.
The results:
10 million cycles:
Time 1: 6382ms, Time 2: 6351ms
Time 1: 6363ms, Time 2: 6351ms
Time 1: 6350ms, Time 2: 6363ms
Time 1: 6353ms, Time 2: 6357ms
Time 1: 6348ms, Time 2: 6354ms
With 10 million cycles, the times are almost the same.
Here are 100 thousand (0.1 million) cycles:
Time 1: 77ms, Time 2: 73ms
Time 1: 94ms, Time 2: 65ms
Time 1: 67ms, Time 2: 63ms
Time 1: 65ms, Time 2: 65ms
Time 1: 66ms, Time 2: 63ms
Also with different amounts of cycles, the getter is a little bit faster than the regular way. I hope this helped you.
Don't use getters setters unless needed for your current delivery I.e. Don't think too much about what would happen in the future, if any thing to be changed its a change request in most of the production applications, systems.
Think simple, easy, add complexity when needed.
I would not take advantage of ignorance of business owners of deep technical know how just because I think it's correct or I like the approach.
I have massive system written without getters setters only with access modifiers and some methods to validate n perform biz logic. If you absolutely needed the. Use anything.
We use getters and setters:
for reusability
to perform validation in later stages of programming
Getter and setter methods are public interfaces to access private class members.
Encapsulation mantra
The encapsulation mantra is to make fields private and methods public.
Getter Methods: We can get access to private variables.
Setter Methods: We can modify private fields.
Even though the getter and setter methods do not add new functionality, we can change our mind come back later to make that method
better;
safer; and
faster.
Anywhere a value can be used, a method that returns that value can be added. Instead of:
int x = 1000 - 500
use
int x = 1000 - class_name.getValue();
In layman's terms
Suppose we need to store the details of this Person. This Person has the fields name, age and sex. Doing this involves creating methods for name, age and sex. Now if we need create another person, it becomes necessary to create the methods for name, age, sex all over again.
Instead of doing this, we can create a bean class(Person) with getter and setter methods. So tomorrow we can just create objects of this Bean class(Person class) whenever we need to add a new person (see the figure). Thus we are reusing the fields and methods of bean class, which is much better.
I spent quite a while thinking this over for the Java case, and I believe the real reasons are:
Code to the interface, not the implementation
Interfaces only specify methods, not fields
In other words, the only way you can specify a field in an interface is by providing a method for writing a new value and a method for reading the current value.
Those methods are the infamous getter and setter....
It can be useful for lazy-loading. Say the object in question is stored in a database, and you don't want to go get it unless you need it. If the object is retrieved by a getter, then the internal object can be null until somebody asks for it, then you can go get it on the first call to the getter.
I had a base page class in a project that was handed to me that was loading some data from a couple different web service calls, but the data in those web service calls wasn't always used in all child pages. Web services, for all of the benefits, pioneer new definitions of "slow", so you don't want to make a web service call if you don't have to.
I moved from public fields to getters, and now the getters check the cache, and if it's not there call the web service. So with a little wrapping, a lot of web service calls were prevented.
So the getter saves me from trying to figure out, on each child page, what I will need. If I need it, I call the getter, and it goes to find it for me if I don't already have it.
protected YourType _yourName = null;
public YourType YourName{
get
{
if (_yourName == null)
{
_yourName = new YourType();
return _yourName;
}
}
}
One aspect I missed in the answers so far, the access specification:
for members you have only one access specification for both setting and getting
for setters and getters you can fine tune it and define it separately
In languages which don't support "properties" (C++, Java) or require recompilation of clients when changing fields to properties (C#), using get/set methods is easier to modify. For example, adding validation logic to a setFoo method will not require changing the public interface of a class.
In languages which support "real" properties (Python, Ruby, maybe Smalltalk?) there is no point to get/set methods.
One of the basic principals of OO design: Encapsulation!
It gives you many benefits, one of which being that you can change the implementation of the getter/setter behind the scenes but any consumer of that value will continue to work as long as the data type remains the same.
You should use getters and setters when:
You're dealing with something that is conceptually an attribute, but:
Your language doesn't have properties (or some similar mechanism, like Tcl's variable traces), or
Your language's property support isn't sufficient for this use case, or
Your language's (or sometimes your framework's) idiomatic conventions encourage getters or setters for this use case.
So this is very rarely a general OO question; it's a language-specific question, with different answers for different languages (and different use cases).
From an OO theory point of view, getters and setters are useless. The interface of your class is what it does, not what its state is. (If not, you've written the wrong class.) In very simple cases, where what a class does is just, e.g., represent a point in rectangular coordinates,* the attributes are part of the interface; getters and setters just cloud that. But in anything but very simple cases, neither the attributes nor getters and setters are part of the interface.
Put another way: If you believe that consumers of your class shouldn't even know that you have a spam attribute, much less be able to change it willy-nilly, then giving them a set_spam method is the last thing you want to do.
* Even for that simple class, you may not necessarily want to allow setting the x and y values. If this is really a class, shouldn't it have methods like translate, rotate, etc.? If it's only a class because your language doesn't have records/structs/named tuples, then this isn't really a question of OO…
But nobody is ever doing general OO design. They're doing design, and implementation, in a specific language. And in some languages, getters and setters are far from useless.
If your language doesn't have properties, then the only way to represent something that's conceptually an attribute, but is actually computed, or validated, etc., is through getters and setters.
Even if your language does have properties, there may be cases where they're insufficient or inappropriate. For example, if you want to allow subclasses to control the semantics of an attribute, in languages without dynamic access, a subclass can't substitute a computed property for an attribute.
As for the "what if I want to change my implementation later?" question (which is repeated multiple times in different wording in both the OP's question and the accepted answer): If it really is a pure implementation change, and you started with an attribute, you can change it to a property without affecting the interface. Unless, of course, your language doesn't support that. So this is really just the same case again.
Also, it's important to follow the idioms of the language (or framework) you're using. If you write beautiful Ruby-style code in C#, any experienced C# developer other than you is going to have trouble reading it, and that's bad. Some languages have stronger cultures around their conventions than others.—and it may not be a coincidence that Java and Python, which are on opposite ends of the spectrum for how idiomatic getters are, happen to have two of the strongest cultures.
Beyond human readers, there will be libraries and tools that expect you to follow the conventions, and make your life harder if you don't. Hooking Interface Builder widgets to anything but ObjC properties, or using certain Java mocking libraries without getters, is just making your life more difficult. If the tools are important to you, don't fight them.
From a object orientation design standpoint both alternatives can be damaging to the maintenance of the code by weakening the encapsulation of the classes. For a discussion you can look into this excellent article: http://typicalprogrammer.com/?p=23
Code evolves. private is great for when you need data member protection. Eventually all classes should be sort of "miniprograms" that have a well-defined interface that you can't just screw with the internals of.
That said, software development isn't about setting down that final version of the class as if you're pressing some cast iron statue on the first try. While you're working with it, code is more like clay. It evolves as you develop it and learn more about the problem domain you are solving. During development classes may interact with each other than they should (dependency you plan to factor out), merge together, or split apart. So I think the debate boils down to people not wanting to religiously write
int getVar() const { return var ; }
So you have:
doSomething( obj->getVar() ) ;
Instead of
doSomething( obj->var ) ;
Not only is getVar() visually noisy, it gives this illusion that gettingVar() is somehow a more complex process than it really is. How you (as the class writer) regard the sanctity of var is particularly confusing to a user of your class if it has a passthru setter -- then it looks like you're putting up these gates to "protect" something you insist is valuable, (the sanctity of var) but yet even you concede var's protection isn't worth much by the ability for anyone to just come in and set var to whatever value they want, without you even peeking at what they are doing.
So I program as follows (assuming an "agile" type approach -- ie when I write code not knowing exactly what it will be doing/don't have time or experience to plan an elaborate waterfall style interface set):
1) Start with all public members for basic objects with data and behavior. This is why in all my C++ "example" code you'll notice me using struct instead of class everywhere.
2) When an object's internal behavior for a data member becomes complex enough, (for example, it likes to keep an internal std::list in some kind of order), accessor type functions are written. Because I'm programming by myself, I don't always set the member private right away, but somewhere down the evolution of the class the member will be "promoted" to either protected or private.
3) Classes that are fully fleshed out and have strict rules about their internals (ie they know exactly what they are doing, and you are not to "fuck" (technical term) with its internals) are given the class designation, default private members, and only a select few members are allowed to be public.
I find this approach allows me to avoid sitting there and religiously writing getter/setters when a lot of data members get migrated out, shifted around, etc. during the early stages of a class's evolution.
There is a good reason to consider using accessors is there is no property inheritance. See next example:
public class TestPropertyOverride {
public static class A {
public int i = 0;
public void add() {
i++;
}
public int getI() {
return i;
}
}
public static class B extends A {
public int i = 2;
#Override
public void add() {
i = i + 2;
}
#Override
public int getI() {
return i;
}
}
public static void main(String[] args) {
A a = new B();
System.out.println(a.i);
a.add();
System.out.println(a.i);
System.out.println(a.getI());
}
}
Output:
0
0
4
Getters and setters are used to implement two of the fundamental aspects of Object Oriented Programming which are:
Abstraction
Encapsulation
Suppose we have an Employee class:
package com.highmark.productConfig.types;
public class Employee {
private String firstName;
private String middleName;
private String lastName;
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getMiddleName() {
return middleName;
}
public void setMiddleName(String middleName) {
this.middleName = middleName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public String getFullName(){
return this.getFirstName() + this.getMiddleName() + this.getLastName();
}
}
Here the implementation details of Full Name is hidden from the user and is not accessible directly to the user, unlike a public attribute.
There is a difference between DataStructure and Object.
Datastructure should expose its innards and not behavior.
An Object should not expose its innards but it should expose its behavior, which is also known as the Law of Demeter
Mostly DTOs are considered more of a datastructure and not Object. They should only expose their data and not behavior. Having Setter/Getter in DataStructure will expose behavior instead of data inside it. This further increases the chance of violation of Law of Demeter.
Uncle Bob in his book Clean code explained the Law of Demeter.
There is a well-known heuristic called the Law of Demeter that says a
module should not know about the innards of the objects it
manipulates. As we saw in the last section, objects hide their data
and expose operations. This means that an object should not expose its
internal structure through accessors because to do so is to expose,
rather than to hide, its internal structure.
More precisely, the Law of Demeter says that a method f of a class C
should only call the methods of these:
C
An object created by f
An object passed as an argument to f
An object held in an instance variable of C
The method should not invoke methods on objects that are returned by any of the allowed functions.
In other words, talk to friends, not to strangers.
So according this, example of LoD violation is:
final String outputDir = ctxt.getOptions().getScratchDir().getAbsolutePath();
Here, the function should call the method of its immediate friend which is ctxt here, It should not call the method of its immediate friend's friend. but this rule doesn't apply to data structure. so here if ctxt, option, scratchDir are datastructure then why to wrap their internal data with some behavior and doing a violation of LoD.
Instead, we can do something like this.
final String outputDir = ctxt.options.scratchDir.absolutePath;
This fulfills our needs and doesn't even violate LoD.
Inspired by Clean Code by Robert C. Martin(Uncle Bob)
If you don't require any validations and not even need to maintain state i.e. one property depends on another so we need to maintain the state when one is change. You can keep it simple by making field public and not using getter and setters.
I think OOPs complicates things as the program grows it becomes nightmare for developer to scale.
A simple example; we generate c++ headers from xml. The header contains simple field which does not require any validations. But still as in OOPS accessor are fashion we generates them as following.
const Filed& getfield() const
Field& getField()
void setfield(const Field& field){...}
which is very verbose and is not required. a simple
struct
{
Field field;
};
is enough and readable.
Functional programming don't have the concept of data hiding they even don't require it as they do not mutate the data.
Additionally, this is to "future-proof" your class. In particular, changing from a field to a property is an ABI break, so if you do later decide that you need more logic than just "set/get the field", then you need to break ABI, which of course creates problems for anything else already compiled against your class.
One other use (in languages that support properties) is that setters and getters can imply that an operation is non-trivial. Typically, you want to avoid doing anything that's computationally expensive in a property.
One relatively modern advantage of getters/setters is that is makes it easier to browse code in tagged (indexed) code editors. E.g. If you want to see who sets a member, you can open the call hierarchy of the setter.
On the other hand, if the member is public, the tools don't make it possible to filter read/write access to the member. So you have to trudge though all uses of the member.
Getters and setters coming from data hiding. Data Hiding means We
are hiding data from outsiders or outside person/thing cannot access
our data.This is a useful feature in OOP.
As a example:
If you create a public variable, you can access that variable and change value in anywhere(any class). But if you create as private that variable cannot see/access in any class except declared class.
public and private are access modifiers.
So how can we access that variable outside:
This is the place getters and setters coming from. You can declare variable as private then you can implement getter and setter for that variable.
Example(Java):
private String name;
public String getName(){
return this.name;
}
public void setName(String name){
this.name= name;
}
Advantage:
When anyone want to access or change/set value to balance variable, he/she must have permision.
//assume we have person1 object
//to give permission to check balance
person1.getName()
//to give permission to set balance
person1.setName()
You can set value in constructor also but when later on when you want
to update/change value, you have to implement setter method.
I have a very common pattern of "given a Foo, return a Bar," for example, given a user_id, return a User.
Is there a conventional naming pattern for these sorts of functions? Following Joel on Software, I've personally used a lot of bar_from_foo(), but I rarely see other people do this and it quickly becomes verbose, e.g.
widgets = user_widgets_from_user(user_from_param_map(params))
Is there a conventional way to name, or namespace (e.g. User.from_map()) in any of the popular languages out there? I am particularly interested in Python but any language you can think of would br useful.
I would take advantage of Clojure's naming flexibility and call it:
(defn foo->bar [] ...)
To me that makes the intent quite clear and it's pretty short.
In Python, and various other OO languages, this should be a constructor on Bar that takes a single Foo as its only argument. Since Python doesn't do method overloading (and attempts to emulate it are usually fragile), if Bar.__init__ already takes a different signature, then the convention is exactly your last one. Importantly, this is usually defined as a class method rather than a static method (for the benefit of subclasses):
class Bar:
#classmethod
def from_foo(cls, f):
'''Create a new Bar from the given Foo'''
ret = cls()
# ...
If you want to convert something into another, for example a string to an integer, the method is to be defined on the receiver, and hence its class is clear, so you should not put the receiver class as part of the method name: String#to_i, not String#string_to_i. This in one of the core ideas of object oriented programming (polymorphism).
If the receiver is too general to be assigned such method, for example if user_id is a mere string, and defining a method on String to convert it to a User does not look right, then you should define a constructor method on the class that you expect the return value to be: User.new or User.from_id.
I think it depends a lot on context and choosing a meaningful metaphor. ActiveRecord for instance uses the class method "find" for finding records in the database, a more meaningful idea than "input a user_id, output a user". For example:
User.find(user_id)
User.find_by_email(user_email)
For conversions, I usually like to write the conversion methods to make it easy to use in higher order functions. For example in ruby, conversions are often done with to_* instance methods, for example to convert a Foo to a Bar it would make sense to have a to_bar method for all foos, so you could write:
foo = Foo.new(...) # make a new Foo
bar = foo.to_bar # convert it to a Bar
And then to convert a bunch of foos, you could simply:
bars = foos.map(&:to_bar)
Ruby also tends to have Foo.parse(str) for converting a string to the object.
For javascript, I like having class methods (which I got from standard ml), for example:
Foo.toBar = function(foo) {
return new Bar(...);
};
And then you can map over it as well (using underscore in this example):
var bars = _.map(foos, Foo.toBar);
the Standard ML convention is structure (class) methods. Example fn types:
Foo.toBar : foo -> bar
Foo.fromBar : bar -> foo
And you'd use it like:
val bar = Foo.toBar foo;
val bars = map Foo.toBar foos;
Why placing the type of the parameter the name of the function? I think it would be clearer something like
a_bar = bar_from(a_foo)
then you can rely on dynamic dispatch or overload in many languages... for example in Python the implementation could try to call x.toBar() if present or it could check for a global registry like Bar_builders[type(x)](x); in Lisp you could rely on methods; in C++ on overloads...
TL;DR:
Do we need factories/constructors in prototypical OO? Can we make a paradigm switch and drop them completely?
The BackStory:
I've been toying with doing prototypical OO in JavaScript lately and find that 99% of OO done in JavaScript is forcing classical OO patterns into it.
My take on prototypical OO is that it involves two things. A static prototype of methods (and static data) and a data binding. We don't need factories or constructors.
In JavaScript these are Object literals containing functions and Object.create.
This would mean we can model everything as a static blueprint/prototype and a data binding abstraction that's preferably hooked straight into a document-style database. I.e. objects are taken out of the database and created by cloning a prototype with the data. This would mean there is no constructor logic, no factories, no new.
The Example code:
An pseudo example would be :
var Entity = Object.create(EventEmitter, {
addComponent: {
value: function _addComponent(component) {
if (this[component.type] !== undefined) {
this.removeComponent(this[component.type]);
}
_.each(_.functions(component), (function _bind(f) {
component[f] = component[f].bind(this);
}).bind(this));
component.bindEvents();
Object.defineProperty(this, component.type, {
value: component,
configurable: true
});
this.emit("component:add", this, component);
}
},
removeComponent: {
value: function _removeComponent(component) {
component = component.type || component;
delete this[component];
this.emit("component:remove", this, component);
}
}
}
var entity = Object.create(Entity, toProperties(jsonStore.get(id)))
The minor explanation:
The particular code is verbose because ES5 is verbose. Entity above is a blueprint/prototype. Any actual object with data would be created by using Object.create(Entity, {...}).
The actual data (in this case the components) is directly loaded from a JSON store and injected directly into the Object.create call. Of course a similar pattern is applied to creating components and only properties that pass Object.hasOwnProperty are stored in the database.
When an entity is created for the first time it's created with an empty {}
The actual Questions:
Now my actual questions are
Open source examples of JS prototypical OO?
Is this a good idea?
Is it in-line with the ideas and concepts behind prototypical OOP?
Will not using any constructors/factory functions bite me in the ass somewhere? Can we really get away with not using constructors. Are there any limitations using the above methodology where we would need factories to overcome them.
I don't think the constructor/factory logic is necessary at all, as long as you change how you think about Object-Oriented Programming. In my recent exploration of the topic, I've discovered that Prototypical inheritance lends itself more to defining a set of functions that use particular data. This isn't a foreign concept to those trained in classical inheritance, but the hitch is that these "parent" objects don't define the data to be operated on.
var animal = {
walk: function()
{
var i = 0,
s = '';
for (; i < this.legs; i++)
{
s += 'step ';
}
console.log(s);
},
speak: function()
{
console.log(this.favoriteWord);
}
}
var myLion = Object.create(animal);
myLion.legs = 4;
myLion.favoriteWord = 'woof';
So, in the above example, we create the functionality that goes along with an animal, and then create an object that has that functionality, along with the data necessary to complete the actions. This feels uncomfortable and odd to anyone who's used to classical inheritance for any length of time. It has none of the warm fuzziness of the public/private/protected hierarchy of member visibility, and I'll be the first to admit that it makes me nervous.
Also, my first instinct, when I see the above initialization of the myLion object is to create a factory for animals, so I can create lions, and tigers, and bears (oh my) with a simple function call. And, I think, that's a natural way of thinking for most programmers - the verbosity of the above code is ugly, and seems to lack elegance. I haven't decided whether that's simply due to classical training, or whether that's an actual fault of the above method.
Now, on to inheritance.
I have always understood inhertance in JavaScript to be difficult. Navigating the ins and outs of the prototype chain is not exactly clear. Until you use it with Object.create, which takes all the function-based, new-keyword redirection out of the equation.
Let's say we wanted to extend the above animal object, and make a human.
var human = Object.create(animal)
human.think = function()
{
console.log('Hmmmm...');
}
var myHuman = Object.create(human);
myHuman.legs = 2;
myHuman.favoriteWord = 'Hello';
This creates an object which has human as a prototype, which, in turn, has animal as a prototype. Easy enough. No misdirection, no "new object with a prototype equal to the prototype of the function". Just simple prototypal inheritance. It's simple, and straightforward. Polymorphism is easy, too.
human.speak = function()
{
console.log(this.favoriteWord + ', dudes');
}
Due to the way the prototype chain works, myHuman.speak will be found in human before it's found in animal, and thus our human is a surfer instead of just a boring old animal.
So, in conclusion (TLDR):
The pseudo-classical constructor functionality was kind of tacked on to JavaScript to make those programmers trained in classical OOP more comfortable. It is not, by any means, necessary, but it means giving up classical concepts such as member visibility and (tautologically) constructors.
What you get in return is flexibility, and simplicity. You can create "classes" on the fly - every object is, itself, a template for other objects. Setting values on child objects will not affect the prototype of those objects (i.e. if I used var child = Object.create(myHuman), and then set child.walk = 'not yet', animal.walk would be unaffected - really, test it).
The simplicity of inheritance is honestly mind-boggling. I've read a lot on inheritance in JavaScript, and written many lines of code attempting to understand it. But it really boils down to objects inherit from other objects. It's as simple as that, and all the new keyword does is muddle that up.
This flexibility is difficult to use to its fullest extent, and I'm sure I have yet to do it, but it's there, and it's interesting to navigate. I think most of the reason that it hasn't been used for a large project is that it simply isn't understood as well as it could be, and, IMHO, we're locked into the classical inheritance patterns we all learned when we were taught C++, Java, etc.
Edit
I think I've made a pretty good case against constructors. But my argument against factories is fuzzy.
After further contemplation, during which I've flip-flopped to both sides of the fence several times, I have come to the conclusion that factories are also unnecessary. If animal (above) were given another function initialize, it would be trivial to create and initialize a new object that inherits from animal.
var myDog = Object.create(animal);
myDog.initialize(4, 'Meow');
New object, initialized and ready for use.
#Raynos - You totally nerd sniped me on this one. I should be getting ready for 5 days of doing absolutely nothing productive.
As per your comment that the question is mainly "is constructor knowledge necessary?" I feel it is.
A toy example would be storing partial data. On a given data set in memory, when persisting I may only choose to store certain elements (either for the sake of efficiency or for data consistency purposes, e.g. the values are inherently useless once persisted). Let's take a session where I store the user name and the number of times they've clicked on the help button (for lack of a better example). When I persist this in my example, I do have no use for the number of clicks, since I keep it in memory now, and next time I load the data (next time the user logs in or connects or whatever) I will initialise the value from scratch (presumably to 0). This particular use case is a good candidate for constructor logic.
Aahh, but you could always just embed that in the static prototype: Object.create({name:'Bob', clicks:0}); Sure, in this case. But what if the value wasn't always 0 at first, but rather it was something that required computation. Uummmm, say, the users age in seconds (assuming we stored the name and the DOB). Again, an item that there is little use persisting, since it will need to be recalculated on retrieval anyway. So how do you store the user's age in the static prototype?
The obvious answer is constructor/initialiser logic.
There are many more scenarios, although I don't feel the idea is much related to js oop or any language in particular. The necessity for entity creation logic is inherent in the way I see computer systems model the world. Sometimes the items we store will be a simple retrieval and injection into a blueprint like prototype shell, and sometimes the values are dynamic, and will need to be initialised.
UPDATE
OK, I'm going to try for a more real-world example, and to avoid confusion assume that I have no database and need not persist any data. Let's say I'm making a solitaire server. Each new game will be (naturally) a new instance of the Game prototype. It is clear to me that their is initialiser logic required here (and lots of it):
I will, for example, need on each game instance not just a static/hard-coded deck of cards, but a randomly shuffled deck. If it were static the user would play the same game every time, which is clearly not good.
I may also have to start a timer to finish the game if the player runs out. Again, not something that can be static, since my game has a few requirements: the number of seconds is inversely related to the number of games the connected player has won so far (again, no saved info, just how many for this connection), and proportional to the difficulty of the shuffle (there is an algorithm that according to the shuffle results can determine the degree of difficulty of the game).
How do you do that with a static Object.create()?
Example of a staticly-clonable "Type":
var MyType = {
size: Sizes.large,
color: Colors.blue,
decay: function _decay() { size = Sizes.medium },
embiggen: function _embiggen() { size = Sizes.xlarge },
normal: function _normal() { size = Sizes.normal },
load: function _load( dbObject ) {
size = dbObject.size
color = dbObject.color
}
}
Now, we could clone this type elsewhere, yes? Sure, we would need to use var myType = Object.Create(MyType), but then we're done, yes? Now we can just myType.size and that is the size of the thing. Or we could read the color, or change it, etc. We haven't created a constructor or anything, right?
If you said there's no constructor there, you're wrong. Let me show you where the constructor is:
// The following var definition is the constructor
var MyType = {
size: Sizes.large,
color: Colors.blue,
decay: function _decay() { size = Sizes.medium },
embiggen: function _embiggen() { size = Sizes.xlarge },
normal: function _normal() { size = Sizes.normal },
load: function _load( dbObject ) {
size = dbObject.size
color = dbObject.color
}
}
Because we've already gone and created all the things we wanted and we've already defined everything. That's all a constructor does. So even if we only clone/use static things (which is what I see the above snippets as doing) we've still had a constructor. Just a static constructor. By defining a type, we have defined a constructor. The alternative is this model of object construction:
var MyType = {}
MyType.size = Sizes.large
But eventually you're going to want to use Object.Create(MyType) and when you do, you will have used a static object to create the target object. And then it becomes the same as the previous example.
The short answer to your question "Do we need factories/constructors in prototypical OO?" is no. Factories/Constructors serve 1 purpose only: initialize the newly created object (an instance) to a specific state.
That being said, it is often uses because some objects need initialization code of some sort.
Let's use the component-based entity code you provided. A typical entity is simply a collection of components and few properties:
var BaseEntity = Object.create({},
{
/* Collection of all the Entity's components */
components:
{
value: {}
}
/* Unique identifier for the entity instance */
, id:
{
value: new Date().getTime()
, configurable: false
, enumerable: true
, writable: false
}
/* Use for debugging */
, createdTime:
{
value: new Date()
, configurable: false
, enumerable: true
, writable: false
}
, removeComponent:
{
value: function() { /* code left out for brevity */ }
, enumerable: true
, writable: false
}
, addComponent:
{
value: function() { /* code left out for brevity */ }
, enumerable: true
, writable: false
}
});
Now the following code will create new entities based on the 'BaseEntity'
function CreateEntity()
{
var obj = Object.create(BaseEntity);
//Output the resulting object's information for debugging
console.log("[" + obj.id + "] " + obj.createdTime + "\n");
return obj;
}
Seems straight forward enough, until you go to reference the properties:
setTimeout(CreateEntity, 1000);
setTimeout(CreateEntity, 2000);
setTimeout(CreateEntity, 3000);
outputs:
[1309449384033] Thu Jun 30 2011 11:56:24 GMT-0400 (EDT)
[1309449384033] Thu Jun 30 2011 11:56:24 GMT-0400 (EDT)
[1309449384033] Thu Jun 30 2011 11:56:24 GMT-0400 (EDT)
So why is this? The answer is simple: because of prototype based inheritance. When we created the objects, there wasn't any code to set the properties id and createdTime on the actual instance, as is normally done in constructors/factories. As a result, when the property is accessed, it pulls from the prototype chain, which ends up being a single value for all entities.
The argument to this is that the Object.create() should be passed the second parameter to set this values. My response would simply be: Isn't that basically the same as calling a constructor or using a factory? It's just another way of setting an object's state.
Now with your implementation where you treat (and rightfully so) all prototypes as a collection of static methods and properties, you do initialize the object by assigning the values of the properties to the data from a data source. It may not be using new or some type of factory, but it is initialization code.
To summarize:
In JavaScript prototype OOP
- new is not needed
- Factories are not needed
- Initialization code is usually needed, which is normally done through new, factories, or some other implementation that you don't want to admit is initializing an object