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Closed 13 years ago.
Other being able to sanity check values in a setter is there a more underlying reason to prefer properties to public variables?
We've had this subject before but I can't find anything now.
In brief: your needs might change: where there's no sanity check now, one might be required in the future. However, if you change your public fields to properties, this breaks binary compatiblity: every client who uses your code/library would have to re-compile.
This is bad because it potentially costs a lot of money.
Using properties from the beginning avoids this problem. This even counts for code that is not part of a library. Why? Because you never know: the code (even if highly domain-specific!) might prove useful so you want to refactor it to a library. This refactoring process is obviously made much easier if you are already using properties in place of public/protected fields.
Additionally, writing public properties is easy in C# 3.0 because you can just use the auto-implemented properties, saving you quite a bit of code:
public DataType MyProperty { get; set; }
Will implement the necessary backing field and getter/setter code for you.
I will add a personal note: .NET's behaviour in this regard is somewhat lazy. The compiler could just change public fields to properties on the fly, thus avoiding the problem. VB6 already did this for COM-exposed classes and I see absolutely no reason for VB.NET and C# not to do the same. Perhaps someone on the compiler teams (Jared?) could comment on this.
In a nutshell:
You can control acces (readonly,
writeonly, read/write)
You can validate values when setting
a property (check for null etc)
You can do additional processing,
such as lazy initialization
You can change the underlying
implementation. For example, a
property may be backed by a member
variable now, but you can change it
to be backed by a DB row without
breaking any user code.
Jeff Atwood has blogged about it:
There are valid reasons to make a trivial property, exactly as depicted above:
Reflection works differently on variables vs. properties, so if you rely on reflection, it's easier to use all properties.
You can't databind against a variable.
Changing a variable to a property is a breaking change.
It's a shame there's so much meaningless friction between variables and properties; most of the time they do the exact same thing. Kevin Dente proposed a bit of new syntax that would give us the best of both worlds:
public property int Name;
However, if the distinction between variable and property is such an ongoing problem, I wonder if a more radical solution is in order. Couldn't we ditch variables entirely in favor of properties? Don't properties do exactly the same thing as variables, but with better granular control over visibility?
Changing a field to a property in the future is considered a breaking change. Fields are considered implementation details of classes and exposing them publicly breaks encapsulation.
Use of properties makes your code more object oriented. By making member variables public, you are exposing your implementation.
Also see this link from C#'s Programming Guide
You can also protect write access and allow read access with a property:
public int Version { get; private set; }
If you work in a closed environment -- you dont develop a SDK, all classes are used within a same project framework -- there is no difference.
The usual argument is that "in the future you may need to do some check on the values, so it is easier with properties". I dont buy it at all.
Using public fields is more readable, less decoration and easier to use.
Yes.
Consider a public varibale which now holds a string, you can simply set it. However, if you decide that that public variable should hold an object which should be initialized with a string then you would have to change all your code using your original object. But if you would have used setter you would only have to change the setter to initialize the object with the provided string.
Related
We're often told we should protect encapsulation by making getter and setter methods (properties in C#) for class fields, instead of exposing the fields to the outside world.
But there are many times when a field is just there to hold a value and doesn't require any computation to get or set. For these we would all do this number:
public class Book
{
private string _title;
public string Title
{
get => _title;
set => _title = value;
}
}
Well, I have a confession, I couldn't bear writing all that (really, it wasn't having to write it, it was having to look at it), so I went rogue and used public fields.
Then along comes C# 3.0 and I see they added automatic properties:
public class Book
{
public string Title { get; set; }
}
Which is tidier, and I'm thankful for it, but really, what's so different than just making a public field?
public class Book
{
public string Title;
}
In a related question I had some time ago, there was a link to a posting on Jeff's blog, explaining some differences.
Properties vs. Public Variables
Reflection works differently on variables vs. properties, so if you rely on reflection, it's easier to use all properties.
You can't databind against a variable.
Changing a variable to a property is a breaking change. For example:
TryGetTitle(out book.Title); // requires a variable
Ignoring the API issues, the thing I find most valuable about using a property is debugging.
The CLR debugger does not support data break points (most native debuggers do). Hence it's not possible to set a break point on the read or write of a particular field on a class. This is very limiting in certain debugging scenarios.
Because properties are implemented as very thin methods, it is possible to set breakpoints on the read and write of their values. This gives them a big leg up over fields.
Changing from a field to a property breaks the contract (e.g. requires all referencing code to be recompiled). So when you have an interaction point with other classes - any public (and generally protected) member, you want to plan for future growth. Do so by always using properties.
It's nothing to make it an auto-property today, and 3 months down the line realize you want to make it lazy-loaded, and put a null check in the getter. If you had used a field, this is a recompile change at best and impossible at worst, depending on who & what else relies on your assemblies.
Just because no one mentioned it: You can't define fields on Interfaces. So, if you have to implement a specific interface which defines properties, auto-properties sometimes are a really nice feature.
A huge difference that is often overlooked and is not mentioned in any other answer: overriding. You can declare properties virtual and override them whereas you cannot do the same for public member fields.
It's all about versioning and API stability. There is no difference, in version 1 - but later, if you decide you need to make this a property with some type of error checking in version 2, you don't have to change your API- no code changes, anywhere, other than the definition of the property.
Another advantage of auto-implemented properties over public fields is that you can make set accessors private or protected, providing the class of objects where it was defined better control than that of public fields.
There is nothing wrong in making a field public. But remember creating getter/setter with private fields is no encapsulation. IMO, If you do not care about other features of a Property, you might as well make it public.
Trivial properties like these make me sad. They are the worst kind of cargo culting and the hatred for public fields in C# needs to stop. The biggest argument against public fields is future-proofing: If you later decide you need to add extra logic to the getter and setter, then you will have to do a huge refactor in any other code that uses the field. This is certainly true in other languages like C++ and Java where the semantics for calling a getter and setter method are very different from those for setting and getting a field. However, in C#, the semantics for accessing a property are exactly the same as those for accessing a field, so 99% of your code should be completely unaffected by this.
The one example I have seen of changing a field into a property actually being a breaking change at the source level is something like:
TryGetTitle(out book.Title); // requires a variable
To this I have to ask, why TF are you passing some other class's field as a reference? Depending on that not being a property seems like the real coding failure here. Assuming that you can directly write to data in another class that you know nothing about is bad practice. Make your own local variable and set book.Title from that. Any code that does something like this deserves to break.
Other arguments I have seen against it:
Changing a field to a property breaks binary compatibility and requires any code that uses it to be recompiled: This is a concern iff you are writing code for distribution as a closed-source library. In that case, yes, make sure none of your user-facing classes have public fields and use trivial properties as needed. If however you are like 99% of C# developers and writing code purely for internal consumption within your project, then why is recompilation a big concern? Just about any other change you make is going to require recompilation too, and so what if it does? Last I checked, it is no longer 1995, we have fast computers with fast compilers and incremental linkers, even larger recompilations shouldn't need more than a few minutes, and it has been quite some time since I have been able to use "my code's compiling" as an excuse for swordfighting through the office.
You can't databind against a variable: Great, when you need to do that, make it into a property.
Properties have features that make them better for debugging like reflection and setting breakpoints: Great, one you need to use one of those things, make it into a property. When you're done debugging and ready to release, if you don't still need those functionalities, change it back into a field.
Properties allow you to override behavior in derived classes: Great, if you are making a base class where you think such a scenario is likely, then make the appropriate members into properties. If you're not sure, leave it as a field and you can change it later. Yes, that will probably require some recompilation, but again, so what?
So in summary, yes there are some legitimate uses for trivial properties, but unless you are making a closed source library for public release, fields are easy enough to convert into properties when needed, and an irrational fear of public fields is just some object oriented dogma that we would do well to rid ourselves of.
For me, the absolute deal breaker for not using public fields was the lack of IntelliSense, showing the references:
Which is not available for fields.
If you decide later to check that the title is unique, by comparing to a collection or a database, you can do that in the property without changing any code that depends on it.
If you go with just a public attribute then you will have less flexibility.
The extra flexibility without breaking the contract is what is most important to me about using properties, and, until I actually need the flexibility, auto-generation makes the most sense.
One thing you can do with Fields but not with Properties (or didn't used to be able to ... I'll come to that in a moment) is that Fields can be designated as readonly whereas Properties cannot. So Fields give you a clear way of indicating your intention that a variable is there to be set (from within the constructor) at object-instantiation time only and should not be changed thereafter. Yes, you can set a Property to have a private setter, but that just says "this is not to be changed from outside the class", which is not the same as "this is not to be changed after instantiation" - you can still change it post-instantiation from within the class. And yes you can set the backing field of your property to be readonly, but that moves post-instantiation attempts to change it to being run-time errors rather than compile-time errors. So readonly Fields did something useful which Properties cannot.
However, that changes with C# 9, whereby we get this helpful syntax for Properties:
public string Height { get; init; }
which says "this can get used from outside of the class but it may only be set when the object is initialized", whereupon the readonly advantage of Fields disappears.
One thing I find very useful as well as all the code and testing reasons is that if it is a property vs a field is that the Visual Studio IDE shows you the references for a property but not a field.
My pov after did some researches
Validation.
Allow overriding the accessor to change the behaviour of a property.
Debugging purpose. We'll be able to know when and what the property change by setting a breakpoint in the accessor.
We can have a field set-only. For instance, public set() and private get(). This is not possible with the public field.
It really gives us more possibility and extensibility.
First just to clarify and avoid unnecessary duplicate tagging, this question is not a duplicate of this one, neither a duplicate of this other one or others I have already searched. Why? they all talk about public fields or private fields WITH the classical C#'s "properties".
My question is why should I write something like this (Public Properties)
class myClass{
public int AValue{get; set;}
}
when I can write instead (Private fields without any properties involved) (Just classic old C++ style way of writing things)
class myClass{
private int aValue;
public int getValue{ return aValue;}
public void setValue(int value){ aValue=value;}
I am scratching my head, reading many many resources, answers and questions, and no one of them answer this question. They all talk about the advantages over public fiels (which I am not asking about) or about the advantages of the new automatic properties over the old ones (which I am not asking either).
I guess my question is why C# does not use the same way of writing that has worked well in Java or C++ that works well. I don't see any advantage. I would very much appreciate someone teaches me the advantage because afaik is not written anywhere else. (not even in my C# books)
From my understanding the public properties that you are referring to are merely syntactic sugar wrapping the pattern that you describe above.
It comes down to readablity and platform standards I guess. While there is nothing wrong with the way that you are talking about, we also need to consider maintainability. To another .Net developer, that pattern does not fit what they are used to and could cause confusion.
And the there is the superficial reason, it is just a lot more code to write. Especially when you have something like a DTO.
The properties in c# are further encapsulated and eventually translated into an intermediate language of a private field and the corresponding Get Set method, so you don't have to be bothered
Auto-accessors are syntactical sugar for exactly that. The generated code has a backing field and get/set methods. Fields don't have accessors, whereas properties do.
Public/private is about encapsulation/security, i.e. who should be able to access your information.
In the way you presented it (writing get and set method) is good, but you have two methods - one for setting the value of the field and one for getting this value. Using properties, it's more natural to me, since you "encapsulate" set and get method under one name and accessing it is better this way (in my opinion).
The main reason for using public int AValue { get; set; } instead of a private field and a getAValue and setAValue pair of functions is that that's just the way that things are done in C#. From a "what the code does at runtime" perspective, the two are pretty much the same as an "auto property" (the type of property you've got where you let the compiler take care of generating a private backing field) compiles down into code very similar to that which you've written (see this stackoverflow questions accepted answer for an example).
The main "advantage" in the context of your question (why use a property instead of a field and a get/set pair of methods) is predictability and comprehensibility. Anyone who's working with your code will expect to see properties, rather than a private field/get/set implementation and thus your code will be more immediately comprehensible to them. Seeing it implemented differently will cause them to question why, assume that there's a reason for it and thus slow them down when it comes to understanding your code.
C#'s getter and setter is syntactic sugar, which remove noisy method names (SetValue or GetValue vs just Value) and increase readability of the code.
Readability is much better in consuming code
// Without properties
var myClass = new MyClass();
myClass.SetAValue(aValue);
myClass.SetBValue(bValue);
//And with properties
var myClass = new MyClass
{
AValue = aValue,
BValue = bValue
}
Because it is only syntactic sugar - every developer/team are free to not use
it.
Some teams have "rules" that properties should be used only for getting/setting values without any "heavy" logic in getters/setters. And methods should be used for setting or getting values which executes some "heavy" operations.
I sometimes use {get; set;} in c# becuase I am told that sometimes technologies I am working with require them (linq2sql?)
I'm wondering why sometimes a technology may require a private field with a getter and setter (and thus the shorthand is a nice shortcut) rather than a public field.
I understand that having logic within a getter or setter makes sense, but not so sure on the point of empty ones?
Is the answer the same as this post, if so just tell me so!
What is exactly the point of auto-generating getters/setters for object fields in Scala?
One reason is Inheritance as your link already points out
One other benefit I can think of is that you can make properties read only by exposing them through public getter. You cannot do this with fields
public String ReadOnlyString {get; private set;}
The point is that it it's bad encapsulation to expose private members to users of your class. By using a property, you can expose the information in a way that allows you to change the internal implementation or storage of that value without the interface changing.
E.g. If you decided to store an integer as a byte to save memory internally, then all calling code would have to be recompiled. This is inconvenient even if you own all the source code, but extremely inconvenient if your code us I a library that somebody else is using.
Another common example is that you may later wish to raise an event if the value is changed.
Other reasons are that some clients may look for properties via reflection, but will not look for member fields - for example, the forms editor and property grids do this.
Also, you can make properties virtual, which can't be done with fields.
Or to look at it from another point of view, what reasons can you think of to_not_ use properties.
This question already has answers here:
What is the difference between a field and a property?
(33 answers)
Closed 8 years ago.
Edit, as per these comments:
Do you mean "Property" vs "Field"?
public String S1; vs public String S2
{ get; set; } – dana
Exactly dana, i mean the same. – Asad
Asad: you really need to try to use
some other term to describe what you
mean so that we can better understand
your question. C# does not have global
variables. The fields you can define
in C# are not global - they are
members of the class type. – dthorpe
Hi fellas,
Need your expert views over the difference between Field and Property. As in my project, I have used certain global variables which later on i changed to 'Properties' . My manager is asking what is the benefit of using Properties of variables instead of Fields.
Although I have replied him that Property provides a kind of secure/safe/indirect access to Field instead of modifying them directly if they are declared public or protected. But Please provide me with some more convincing arguments.
Thanks and Regards
#Asad:
You should get your terminology right: Fields are not Global Variables, C# does not have global variables (as a few commenters mentioned: you can simulate global variables, but you should not do that).
The main advantage is that you can attach all sorts of functionality to a property such as validation, synchronization etc. You can't do that for a class field. For example, a field can throw BCL exceptions on assignment but it can't throw an exception that make sense with logic in your problem domain.
Also imagine trying to protect a field for thread synchronization. You have to write extra code in all the places in your code where the field is accessed. To do that with a property you can simply wrap the getter and setter with a lock in one place. (But beware! The ease of using lock in property getters and setters can give you a false sense of security if you're working with mutable types. See the accepted answer in this post.)
Now, you might think that validation and synchronization are not important to you for this particular value, and they may never be for this particular instance. But by using properties instead of direct field access is making your application much more maintainable in the future. (Suppose the value of an integer field suddenly needs to come from a source different from the original implementation and it needs to be converted from a string to an int. If you use properties to wrap the field then you make the change in one place and all the client code that uses that property does not need to change at all!)
Also, for managing information shared across many classes (global) take a look at the singleton pattern. But beware! Even though it looks neat and clean you can still get into trouble with it. Though if you really need global data you should use properties contained in a singleton. If nothing else, it's a good organization strategy.
To avoid issues with singletons or "global" data take a look at dependency injection as a much better alternative.
C# syntax doesn't have a "global variable" declaration. It has properties and fields, and static properties and fields.
If by "global variable" you mean a static field or static property, that is different from a property or field in that the static field or property is not stored in the object instance data, it is stored in global memory. The value assigned to a static field or property is accessible to all instances of that class, and all instances see the same value. A static field is the closest thing C# has to the notion of "global variable" found in other programming languages.
A non-static property or field stores its data in the object instance data, so each instance of the object has its own local copy. Modifying object1.A property will not affect the value of object2.A property.
Have a look at Properties (C# Programming Guide)
A property is a member that provides a
flexible mechanism to read, write, or
compute the value of a private field.
Properties can be used as if they are
public data members, but they are
actually special methods called
accessors. This enables data to be
accessed easily and still helps
promote the safety and flexibility of
methods.
Properties enable a class to expose a
public way of getting and setting
values, while hiding implementation
or verification code.
A get property accessor is used to
return the property value, and a set
accessor is used to assign a new
value. These accessors can have
different access levels.
Properties that do not implement a
set accessor are read only.
I prefer properties because then when I use them in code I know exactly which class was used to call them (ex. class.property = value). Public class variables can become a real pain and waste of time when you are trying to figure out where they came from during debugging.
This question already has answers here:
Are there any reasons to use private properties in C#?
(19 answers)
Closed 9 years ago.
For private class variables, which one is preferred?
If you have a property like int limit, you want it to be:
int Limit {get; set;}
and use it inside the class, like so:
this.Limit
Is there a reason to use it or not use it? Maybe for performance reasons?
I wonder if this is a good practice.
For a private member, I only make it a property when getting and/or setting the value should cause something else to occur, like:
private int Limit
{
get
{
EnsureValue();
return this._limit;
}
}
Otherwise, fields are fine. If you need to increase their accessibility, it's already a big enough change that making it a property at that point isn't a huge deal.
Edit: as Scott reminds us in the comments, side effects in properties can often cause more pain than anything else. Don't violate Single Responsibility and limit property logic to consistent, logical operations on the value only that must be done at the gate - such as lazy loading (as in the example above), transforming an internal structure into a publicly-useful format, etc.
The only real benefit an auto-property has over a field when the accessibility is private is that you can set a breakpoint on accesses and updates of the variable. If that is important to your scenario then definitely use an auto-property. Otherwise, given there is no substantial advantage, I choose to go with the simplest construct which is a field.
I would say its good practice to use a property. If ever you had to expose the limit value and used a local member it will require more coding while if its a property it would only require a change of its modifier.
I think it's cleaner also.
Granted, since it's a private API, its an implementation detail - you can do whatever you want here. However, there is very little reason to not use a property, even for private classes. The properties get inlined away by the JIT, unless there is extra code in place, so there isn't really a performance impact.
The biggest reasons to prefer properties, IMO, are:
Consistency in your API - You'll want properties in publicly exposed APIs, so making them in the private API will make your programming exprience more consistent, which leads to less bugs due to better maintainability
Easier to convert private class to public
From my perspective, using properties in lieu of variables boils down to:
Pros
Can set a break point for debugging, as Jared mentioned,
Can cause side-effects, like Rex's EnsureValue(),
The get and set can have different access restrictions (public get, protected set),
Can be utilized in Property Editors,
Cons
Slower access, uses method calls.
Code bulk, harder to read (IMO).
More difficult to initialize, like requiring EnsureValue();
Not all of these apply to int Limit {get; set;} style properties.
The point of automatic properties is they are very quick at creating a public access to some field in your class. Now, they offer no benefit over exposing straight up fields to the outside world, other than one big one.
Your class' interface is how it communicates with the outside world. Using automatic properties over fields allows you to change the internals of your class down the road in case you need to make setting the value of that property do something or check authorization rules or something similar on the read.
The fact that you already have a property means you can change your implementation without breaking your public interface.
Therefore, if this is just a private field, an automatic property isn't really that useful, not only that, but you can't initialize public properties at declaration like you can with fields.
I generally follow the following principle: If it's for strictly private use, use a field as it is faster.
If you decide that it should become public, protected or internal some day, it's not difficult to refactor to a property anyway, and with tools like ReSharper, it takes about 3 seconds to do so... :)
There's nothing wrong with having private or protected properties; this is mostly useful when there is some rule or side effect associated with the underlying variable.
The reason why properties seem more natural for public variables is that in the public case, it is a way to hedge one's bet against future implementation changes, whereby the property will remain intact but the implementation details somehow move around (and/or some additional business rule will be needed).
On performance, this is typically insignificant, or indeed identical for straight-assignment properties.
I personally dislike (but often use) plain assignment properties because they just clutter the code. I wish C# would allow for "after the fact refactoring".
Properties provide some very good automatic features (like Json and Xml Serialization)
Fields do not.
Properties can also be a part of an Interface. If you decide to refactor later on... this might be something to consider too.
Properties are just syntactic sugar, C# will compile them into get_PropertyName and set_PropertyName, so performance differences are not a consideration.
If your data member need only set and get logic then properties are very good and fast solution in C#