We Keep Coding

C# automatic properties vs regular local variables [duplicate]

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.

The semantic difference between a property and a field, and their implications

Take private string Property {get; set;} versus private string field.
Note that both are private (so they will not be exposed outside of this class) and that the property is not employing extra validation.
As regards semantics, do they have different meanings? In the sense that, are they interchangeable when used like this?
And when it comes to implications, such as (micro?) performance, does it matter if you create a field versus a property i.e. letting the compiler take care of the backing field for you.

When they're private the only difference I know is that the property is not suitable for out and ref parameters.
But mostly a private property does not deliver any advantages (over a field), so why bother?
There probably are (micro) performance costs. I would worry more about the extra clutter.

A property is about data hiding of a field
A private property does not mean much, since whoever has access to the property, will have access to the field as well
There is no performance implication for auto-property versus backing field since compiler spits out the backing field but there can be serialisation/deserialisation caveats.
UPDATE
Performance implications:
There is a slight performance in using property (auto or with backing field) vs field since a property is a method and a CLR virtcall needs to be called.
But as I said, there is not much point in using property and I believe a field is more readable as usually immediately visible by the naming convention (starting with underscore or camel casing).

You can't have a reference to a property, but you can get a reference to a member. Thus, if you use members, you might have trouble switching them to properties for whatever reason later, such as adding the notorious validation.

Creating a private automatic property has no use that I can see. If its not automatic it could be used as some kind of internal 'event handler' to keep the object state up to date: perform some actions every time the field changes (through the setter) anywhere in the code.
Performance? I dont think there would be an issue, not even at a micro micro level.

Properties ARE functions.
Fields are 'variables with at least class visibility'.
So if you have private property vs private field:
The difference from the performance point:
no difference if you use optimization and no trace (properties are treated as inlines).
The difference in semantics:
1) Formally no difference.
2) More deeply, there IS a difference. Since properties are functions you CAN get a delegate from getter and setter. And CAN use the delegate as... delegate, like putting this delegate to the list with other delegates (Create a delegate from a property getter or setter method)
The difference from a design view:
But properties are functions that looks like variables. Why one could need functions that look like variables?
Lets say you have class Hand and this hand has variable fingersNumber.
class Hand
{
public int fingersNumber;
}
Then you may have a lot of code like
if(he is BadPerson) leftHand.fingersNumber--
if(doctor.Heal()) leftHand.fingersNumber++
But at some point you may want to add some other variable to Hand. Lets say it is ringsNumber. And you know, that you can't have more than 10 rings for each finger.
class Hand
{
public int fingersNumber;
public int ringsNumber;
}
now, you cannot just do
leftHand.fingersNumber--
because you have to control ringsNumber on fingersNumber dependence.
So you have to create some functions that whould check this dependance. Also you have to hide fingersNumber ander ringsNumber from users so they cannot change this fields without the check.
class Hand
{
private int fingersNumber;
private int ringsNumber;
public int GetFingersNumber(){...check logic...}
public void SetFingersNumber(int value){...check logic...}
public int GetRingsNumber(){...check logic...}
public void SetRingsNumber(int value){...check logic...}
}
And use this functions as
if(he is BadPerson) leftHand.SetFingersNumber(leftHand.GetFingersNumber()-1)
The problem here that the old code leftHand.fingersNumber-- would not work now. And from the beginning you wouldn't know that one will add rings in the future. To solve the problems it became a paradigm to set fields as private and use Set and Get functions to get and change variables and BE SURE that in the future one could add any logic there and code would work!
Setters and Getters is a current situation in C++, Java and many languages.
But C# creators went further and decorated such getters and setters functions as "properties".
class Hand
{
private int fingersNumber;
public int FingersNumber
{
get{return fingersNumber;}
set{fingersNumber=value;}
}
...
}
...
if(he is BadPerson) leftHand.FingersNumber--;
But most of the time people create such simple property and, you see the example, it is 5 lines of routine code. So at some version of C# autoproperties was added to simplify life of programmers. So your class is probably looks like
class Hand
{
public int FingersNumber{get;set;}
}
but at any time you can extend this get set behaviour:
class Hand
{
private int fingersNumber;
public int FingersNumber
{
get{...check logic...}
set{...check logic...}
}
...
}
And it will NOT BRAKE ANY CODE. Like
if(he is BadPerson) leftHand.FingersNumber--;
So thats what are the properties, why do they used and what is the difference with fields.
Also as I ser earlier, simple properties and autoproperties have the same performance as variables if you use optimization. Se disassembly or just google about it.

Properties vs. Fields: Need help grasping the uses of Properties over Fields

First off, I have read through a list of postings on this topic and I don't feel I have grasped properties because of what I had come to understand about encapsulation and field modifiers (private, public..ect).
One of the main aspects of C# that I have come to learn is the importance of data protection within your code by the use of encapsulation. I 'thought' I understood that to be because of the ability of the use of the modifiers (private, public, internal, protected). However, after learning about properties I am sort of torn in understanding not only properties uses, but the overall importance/ability of data protection (what I understood as encapsulation) within C#.
To be more specific, everything I have read when I got to properties in C# is that you should try to use them in place of fields when you can because of:
1) they allow you to change the data type when you can't when directly accessing the field directly.
2) they add a level of protection to data access
However, from what I 'thought' I had come to know about the use of field modifiers did #2, it seemed to me that properties just generated additional code unless you had some reason to change the type (#1) - because you are (more or less) creating hidden methods to access fields as opposed to directly.
Then there is the whole modifiers being able to be added to Properties which further complicates my understanding for the need of properties to access data.
I have read a number of chapters from different writers on "properties" and none have really explained a good understanding of properties vs. fields vs. encapsulation (and good programming methods).
Can someone explain:
1) why I would want to use properties instead of fields (especially when it appears I am just adding additional code
2) any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code?
3) Any general rules of thumb when it comes to good programming methods in relation to when to use what?
Thanks and sorry for the long post - I didn't want to just ask a question that has been asked 100x without explaining why I am asking it again.

1) why I would want to use properties
instead of fields (especially when it
appears I am just adding additional
code
You should always use properties where possible. They abstract direct access to the field (which is created for you if you don't create one). Even if the property does nothing other than setting a value, it can protect you later on. Changing a field to a property later is a breaking change, so if you have a public field and want to change it to a public property, you have to recompile all code which originally accessed that field.
2) any tips on recognizing the use of
properties and not seeing them as
simply methods (with the exception of
the get;set being apparent) when
tracing other peoples code?
I'm not totally certain what you are asking, but when tracing over someone else's code, you should always assume that the property is doing something other than just getting and setting a value. Although it's accepted practice to not put large amounts of code in getters and setter, you can't just assume that since it's a property it will behave quickly.
3) Any general rules of thumb when it
comes to good programming methods in
relation to when to use what?
I always use properties to get and set methods where possible. That way I can add code later if I need to check that the value is within certain bounds, not null etc. Without using properties, I have to go back and put those checks in every place I directly accessed the field.

One of the nice things about Properties is that the getter and the setter can have different levels of access. Consider this:
public class MyClass {
public string MyString { get; private set; }
//...other code
}
This property can only be changed from within, say in a constructor. Have a read up on Dependency Injection. Constructor injection and Property injection both deal with setting properties from some form of external configuration. There are many frameworks out there. If you delve into some of these you will get a good feel for properties and their use. Dependency injection will also help you with your 3rd question about good practice.
When looking at other people's code, you can tell whether something is a method or a property because their icons are different. Also, in Intellisence, the first part of a property's summary is the word Property.

You should not worry about the extra code needed for accessing fields via properties, it will be "optimized" away by the JIT compiler (by inlining the code). Except when it is too large to be inlined, but then you needed the extra code anyway.
And the extra code for defining simple properties is also minimal:
public int MyProp { get; set; } // use auto generated field.
When you need to customize you can alway define your own field later.
So you are left with the extra layer of encapsulation / data protection, and that is a good thing.
My rule: expose fields always through properties

While I absolutely dislike directly exposing fields to the public, there's another thing: Fields can't be exposed through Interfaces; Properties can.

There are several reasons why you might want to use Properties over Fields, here are just a couple:
a. By having the following
public string MyProperty { get; private set; }
you are making the property "read only". No one using your code can modify it's value. There are cases where this isn't strictly true (if your property is a list), but these are known and have solutions.
b. If you decide you need to increase the safety of your code use properties:
public string MyProperty
{
get { return _myField; }
set
{
if (!string.IsNullOrEmpty(value))
{
_myField = value;
}
}
}
You can tell they're properties because they don't have (). The compiler will tell you if you try to add brackets.
It's considered good practise to always use properties.

There are many scenarios where using a simple field would not cause damage, but
a Property can be changed more easily later, i.e. if you want to add an event whenever the value changes or want to perform some value/range checking.
Also, If you have several projects that depend on each other you have to recompile all that depend on the one where a field was changed to a property.

Using fields is usually practiced in private classes that is not intended to share data with other classes, When we want our data to be accessible by other classes we use properties which has the ability to share data with other classes through get and set which are access methods called Auto Properties that have access to data in private classes, also you can use both with access modifiers Full Property in the same class allowing the class to use data privately as data field and in the same time link the private field to a property that makes the data accessible to other classes as well, see this simple example:
private string _name;
public string Name
{
get
{
return _name;
}
set
{
_name = value;
}
}
The private string _name is used by the class only, while the Name property is accessible by other classes in the same namespace.

why I would want to use properties instead of fields (especially when it appears I am just adding additional code
You want to use properties over fields becuase, when you use properties you can use events with them, so in a case when you want to do some action when a property changes, you can bind some handlers to PropertyChanging or PropertyChanged events. In case of fields this is not possible. Fields can either be public or private or protected, in case of props you can make them read-only publicly but writable privately.
any tips on recognizing the use of properties and not seeing them as simply methods (with the exception of the get;set being apparent) when tracing other peoples code?
A method should be used when the return value is expected to be dynamic every-time you call, a property should be used when the return value is not that greatly dynamic.
Any general rules of thumb when it comes to good programming methods in relation to when to use what?
Yes, I strongly recommend to read Framework Design guidelines for best practices of good programming.

Properties are the preferred way to cover fields to enforce encapsulation. However, they are functional in that you can expose a property that is of a different type and marshal the casting; you can change access modifiers; they are used in WinForms data binding; they allow you to embed lightweight per-property logic such as change notifications; etc.
When looking at other peoples code, properties have different intellisense icons to methods.
If you think properties are just extra code, I would argue sticking with them anyway but make your life easier by auto-generating the property from the field (right-click -> Refactor -> Encapsulate Field...)

Properties allow you to do things other than set or get a value when you use them. Most notably, they allow you to do validation logic.
A Best Practice is to make anything exposed to the public a Property. That way, if you change the set/get logic at a later time, you only have to recompile your class, not every class linked against it.

One caveat is that things like "Threading.Interlocked.Increment" can work with fields, but cannot work with properties. If two threads simultaneously call Threading.Interlocked.Increment on SomeObject.LongIntegerField, the value will get increased by two even if there is no other locking. By contrast, if two threads simultaneously call Threading.Interlocked.Increment on SomeObject.LongIntegerProperty, the value of that property might get incremented by two, or by one, or by -4,294,967,295, or who knows what other values (the property could be written to use locking prevent values other than one or two in that scenario, but it could not be written to ensure the correct increment by two).

I was going to say Properties (setters) are a great place to raise events like NotifyPropertyChanged, but someone else beat me to it.
Another good reason to consider Properties: let's say you use a factory to construct some object that has a default constructor, and you prepare the object via its Properties.
new foo(){Prop1 = "bar", Prop2 = 33, ...};
But if outside users new up your object, maybe there are some properties that you want them to see as read-only and not be able to set (only the factory should be able to set them)? You can make the setters internal - this only works, of course, if the object's class is in the same assembly as the factory.
There are other ways to achieve this goal but using Properties and varying accessor visibility is a good one to consider if you're doing interface-based development, or if you expose libraries to others, etc.

Why use private members then use public properties to set them?

Seen a few examples of code where this happens:
public class Foo
{
string[] m_workID;
public string[] WorkID
{
get
{
return m_workID;
}
private set
{
m_workID = value;
}
}
}
What's the point of this?
Since the use m_workID unnescessary.

In general, the point is to separate implementation (the field) from API (the property).
Later on you can, should you wish, put logic, logging etc in the property without breaking either source or binary compatibility - but more importantly you're saying what your type is willing to do, rather than how it's going to do it.
I have an article giving more benefits of using properties instead of public fields.
In C# 3 you can make all of this a lot simpler with automatically implemented properties:
public class Foo
{
public string[] WorkID { get; private set; }
}
At that point you still have a public getter and a private setter, but the backing field (and property implementation) is generated for you behind the scenes. At any point you can change this to a "normal" fully-implemented property with a backing field, and you'll still have binary and source compatibility. (Compatibility of serialized objects is a different matter, mind you.)
Additionally, in this case you can't mirror the behaviour you want (the ability to read the value publicly but write it privately) with a field - you could have a readonly field, but then you could only write to it within the constructor. Personally I wish there were a similar shorthand for this:
public class Foo
{
private readonly int id;
public int Id { get { return id; } }
...
}
as I like immutable types, but that's a different matter.
In another different matter, it's generally not a good idea to expose arrays like this anyway - even though callers can't change which array WorkID refers to, they can change the contents of the array, which is probably not what you want.
In the example you've given you could get away without the property setter, just setting the field directly within the same class, but it would mean that if you ever wanted to add logging etc you'd have to find all those writes.

A property by itself doesn't provide anywhere to put the data - you need the field (m_workID) for storage, but it entirely correct to hide that behind a property for many, many reasons. In C# 3.0 you can reduce this to:
public string[] WorkID {get; private set;}
Which will do much of the same. Note that exposing an array itself may be problematic, as there is no mechanism for protecting data in an array - at least with an IList<string> you could (if needed) add extra code to sanity check things, or could make it immutable. I'm not saying this needs fixing, but it is something to watch.

In addition to the Object Oriented philosophy of data encapsulation, it helps when you need to do something every time your property is read/write.
You can have to perform a log, a validation, or any another method call later in your development.
If your property is public, you'll have to look around all your code to find and modify your code. And what if your code is used as a library by someone else ?
If your property is private with appropriate get/set methods, then you change the get/set and that's all.

You can use C# 3.0 auto properties feature to save time typing:
public class Foo
{
public string[] WorkID
{
get; private set;
}
}
In addition properties gives you lot of advantages in comparison to fields:
properties can be virtual
properties hide implementation details (not all properties are just trivial variable accessors)
properties can contain validation and logging code and raise change events
interfaces cannot contains fields but properties

A lot of times you only want to provide read access to a field. By using a property you can provide this access. As you mention you may want to perform operations before the field is accessed (lazy loading, e.g.). You have a lot of code in there that just isn't necessary anymore unless you're still working in .Net 2.0-.

Disadvantages of using properties only with no corresponding fields in .NET?

I have classes which have automatic properties only like public customerName {get; set;}. They are public because they are accessed outside the class. They can also be accessed inside the class. They offer good encapsulation and better debugging. I can put a breakpoint on one if I need to know who is accessing it and when.
My question is what are the disadvantages of using properties only with no corresponding fields? I can make the setter or getter private, internal.. etc which means I also have flexibility of scoping it when needed.

Serialization with BinaryFormatter - you have big problems if you need to change your property to a "regular" property later, for example to add some validation / eventing /etc - sinc BinaryFormatter uses the field names. And you can't duplicate this, since the field name the compiler generates cannot be written as legal C#.
Which is a good reason to look at a contract-based serializer instead. See this blog entry for more info.

You can't create truly read only property, because you have to define both setter and getter. You can only use private setter to achieve pseudo-readonly property from outside.
Otherwise, as said above there are no other disadvantages.

There are no disadvantages for simple properties. The compiler creates the backing field for you. This blog entry explains how the compiler treats automatically implemented properties.

Not really a disadvantage, but you have to be aware of the default values of automatic properties. With "classic" properties we always used to initialize the backing fields, e.g. like this:
private bool _flag = true;
public bool Flag
{
get { return _flag; }
set { _flag = value; }
}
This made it obvious what the default value of the property is.
With automatic properties, you have to know what the default values are for the different types (e.g. false for bool). If you don't want the property to have the default value you have to initialize it in the constructor:
class MyClass
{
public bool Flag { get; set; }
public MyClass()
{
Flag = true;
}
}
This means, you have to implement a constructor if you want to initialize your properties to non default values or if a property is of a reference type (class).
But as I wrote, I do not really think of this as a disadvantage, just something you have to know.

The thing is, there is a corresponding field. You just don't see it because the compiler creates it for you. Automatic properties are just syntactic sugar or shorthand way to create the field.

No major things. Just edge cases like where you need to pass a property to a method where the parameter is passed by reference (ref or out) which isn't possible with a property (because internally, they're just get_Property/set_Property methods implemented by the compiler, not special fields of some kind) and you would need an explicit private backing field for this.
EDIT: Oh, and seconding the 'no readonly' properties, which is actually fairly common.

If you don't need to perform any specific logic in the get and/or set accessors, there's no disadvantage...

I say that they are bad from a code readability standpoint. Syntax sugar is nice for writing code but horrible for reading code. As developers the code we leave behind will ultimately be inherited by some poor developer that will have to make sense out of what we did and what is going on in the code. I really am against changing a language to simply save keystrokes when there is an established syntax for the same constructs.