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What does the Auto Property give me over a simple Field? [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.

Using a private auto property instead of a simple variable for a programming standard

In a discussion with a peer, it was brought up that we should consider using auto properties for all class level variables... including private ones.
So in addition to a public property like so:
public int MyProperty1 { get; set; }
Our private class-level variables would look like this:
private int MyProperty2 { get; set; }
Instead of:
private int _myProperty2;
I'm on the fence about why someone would want to do this but I can't decide if my reluctance to accept this is because of my own internal brainwashing with how I write my code to the same programming standards and naming conventions I've used for 10 years or because I've never seen this before (for a reason).
I realize it's extra code to type but to be honest, when using auto-properties, I don't think I've ever typed it out due to the 'prop' and 'propg' snippets so it'd be very simple to set up a new snippet to create a private auto property so the extra code doesn't bother me too much since I never have to type it.
Other than aesthetics which may just be my subconscious, are there any issues that could result from using fully private auto properties? Are there any good reasons to do this or not to do it? I've seen a lot of code in my day on stackoverflow, codeplex, codeproject, etc. and I've never seen anyone use this standard.... is there a reason why?

Private auto-properties are completely pointless, in my opinion. What value does a private auto-property provide that a plain field doesn't?
(It's different when the auto-property is only partially private -- eg, a public/protected getter with a private setter -- or when you use a private non-automatic property to enable you to wrap additional code around the getter/setter.)

This does not make too much sense.
I can think of a 'benefit':
you can later add logic to the getter and/or setter and be sure it is always passed
but frankly your classes should not become so big that this is useful.
"are there any issues" ?
Your properties won't work as arguments to ref or out parameters.

It's not nearly as useful for privates as for publics.
Suppose you took your automatic private property and later built some logic into it (being able to do that without breaking anything is the whole point of auto props)...
This would require you to create a private backing member for the property to wrap.
So now you've got two different private ways (member and property) of doing the same thing though one has hidden side effects (the property) and you've now also got the problem of ensuring none of your other methods in the class access that member directly.
Ends up being much more of a headache than just using a private member from the beginning.

What this strategy will do for you is provide an opportunity to put any future changes into the previously autogenerated private property without affecting any of the other code that gets or sets your private property. I personally haven't used this much but it can be beneficial in a case where changes to handling may occur. It also standardizes the code so that fields are always accessed by properties. There are no real drawbacks but it is not really much benefit in most situations either. I think style is really the biggest driver in most situations.

In a discussion with a peer, it was
brought up that we should consider
using auto properties for all class
level variables... including private
ones.
This will not be useful, In case you don't have any logic to write in your properties for retrieving and returning values.
Besides point 1, you have read only property
So you can directly go with
public int MyProperty1 { get; set; }
Moreover it reduces your line of code and Quick Implementation

I'm a firm believer in KISS. I never use a property when a field will do, and I see very little reason to use private accessors (get).
The primary purpose of a property is to be a public accessor for private data. So for simple propreties that do nothing but set or get a value, private accessors and setters make no sense.
Having said that, when you need to transform the data as it's being read, or when you need to perform a side effect when updating the value, you should use a field. Does changing your value raise an event? Then a field is a no-brainer. But then, that's not an auto field that you're declaring with {get; set;}

What is the difference...? [C# properties GET/SET ways]

I know in C# you can easily create accessors to a data type, for example, by doing the following:
public class DCCProbeData
{
public float _linearActual { get; set; }
public float _rotaryActual { get; set; }
}
However my colleague, advised me to do it this way:
public class DCCProbeData
{
private float _linearActual = 0f;
public float LinearActual
{
get { return _linearActual; }
set { _linearActual = value; }
}
private float _rotaryActual = 0f;
public float RotaryActual
{
get { return _rotaryActual; }
set { _rotaryActual = value; }
}
}
My way seems simpler, and more concise. What are the differences and benefits of doing it either way?
Thanks
Edit Just a note, my colleague was able to generate the code for the "second way" using the Refactor option within the Class Details pane most easily found in a Diagram file. This makes it easy to add many Properties without having to manually create the accessors.

"Your way" just tells the compiler to create the second option. Unless you do something else in the getter or setter, they are functionally identical.
However, with "your way", I would recommend using the proper C# naming conventions. I would personally write this as:
public class DccProbeData
{
public float LinearActual { get; set; }
public float RotaryActual { get; set; }
}

The only difference is that you've named the fields.
(I'd stick with your colleagues naming convention for public properties though.)

They do the same thing internally. The only difference is that you cannot directly access the backing field variable using Auto Implemented Properties.

They are technically the same... the get/set is shorthand (auto property).
Lots of questions on SO about this:
When to use get; set; in c#
What is the { get; set; } syntax in C#?
Auto-Implemented Properties c#

Your way doesn't allow you to initialize the values, and your colleague's way follows a more-standard naming convention.

I would like to add something that I haven't seen in the other answers, which makes #2 a better choice:
Using the first method you cannot set a breakpoint on the get and set.
Using the second method you can set a breakpoint on the get and set, which is very helpful for debugging anything accessing your private variable.

Okay, the names have been mentioned before. It's also worth noting that as well as not being with the normal .NET conventions, beginning a public name with an underscore is not CLS-compliant (indeed, one reason for using it for private names is precisely because of this, it makes the distinction clearer, and should result in a warning with some code-checkers if you accidentally have the wrong access level).
Names aside, the one advantage to the latter form is that you can add more complicated code. Still, it's a non-breaking change to go from the former style to the latter, so there's no reason to do it before it's needed.

The first way is the way to go when you need simple properties with get and set and private storage done for you.
Use the second way if you need to do something special when you get or set the value.
Also, I recommend you stick to naming conventions using FxCop or ReSharper.

I believe at the IL level, they both end up the same. In the background, VS creates autonamed variables for you when using the auto getters and setters.

The only way this could possibly be better is if you feel you will be adding more logic to the getters and setters at a later date.
Even then, this seems a little pointless.

They are the same in the sense that your code sample will automatically generate backing fields.
But the two code samples are different because the names of the properties are not the same (LinearActual vs linearActual)

There is no difference, however prior to C# 3 you had to use the long way. At the end of the day it's a C# feature - syntactic sugar. They are both functionally identical.

Things you can do when you don't use auto-implemented properties:
initialize to a default value
access or annotate the backing field (attributes)
read-only backing fields or immutability
set a breakpoint on access
have custom code around access to the variable
Use [System.ComponentModel.EditorBrowsableAttribute()] to enable custom logic on the accessors that you avoid accidently bypassing while coding
hides the backing field from intellisense
Conversion between the two ways is made very simple with ReSharper.
This is not to say don't use them by all means use them, unless you have a need for any of the other functionality listed.

Are there any reasons to use private properties in C#?

I just realized that the C# property construct can also be used with a private access modifier:
private string Password { get; set; }
Although this is technically interesting, I can't imagine when I would use it since a private field involves even less ceremony:
private string _password;
and I can't imagine when I would ever need to be able to internally get but not set or set but not get a private field:
private string Password { get; }
or
private string Password { set; }
but perhaps there is a use case with nested / inherited classes or perhaps where a get/set might contain logic instead of just giving back the value of the property, although I would tend to keep properties strictly simple and let explicit methods do any logic, e.g. GetEncodedPassword().
Does anyone use private properties in C# for any reason or is it just one of those technically-possible-yet-rarely-used-in-actual-code constructs?
Addendum
Nice answers, reading through them I culled these uses for private properties:
when private fields need to be lazily loaded
when private fields need extra logic or are calculated values
since private fields can be difficult to debug
in order to "present a contract to yourself"
to internally convert/simplify an exposed property as part of serialization
wrapping global variables to be used inside your class

I use them if I need to cache a value and want to lazy load it.
private string _password;
private string Password
{
get
{
if (_password == null)
{
_password = CallExpensiveOperation();
}
return _password;
}
}

The primary usage of this in my code is lazy initialization, as others have mentioned.
Another reason for private properties over fields is that private properties are much, much easier to debug than private fields. I frequently want to know things like "this field is getting set unexpectedly; who is the first caller that sets this field?" and it is way easier if you can just put a breakpoint on the setter and hit go. You can put logging in there. You can put performance metrics in there. You can put in consistency checks that run in the debug build.
Basically, it comes down to : code is far more powerful than data. Any technique that lets me write the code I need is a good one. Fields don't let you write code in them, properties do.

perhaps there is a use case with nested / inherited classes or perhaps where a get/set might contain logic instead of just giving back the value of the property
I personally use this even when I don't need logic on the getter or setter of a property. Using a property, even a private one, does help future-proof your code so that you can add the logic to a getter later, if required.
If I feel that a property may eventually require extra logic, I will sometimes wrap it into a private property instead of using a field, just so I don't have to change my code later.
In a semi-related case (though different than your question), I very frequently use the private setters on public properties:
public string Password
{
get;
private set;
}
This gives you a public getter, but keeps the setter private.

One good usage for private get only properties are calculated values. Several times I've had properties which are private readonly and just do a calculation over other fields in my type. It's not worthy of a method and not interesting to other classes so private property it is.

Lazy initialization is one place where they can be neat, e.g.
private Lazy<MyType> mytype = new Lazy<MyType>(/* expensive factory function */);
private MyType MyType { get { return this.mytype.Value; } }
// In C#6, you replace the last line with: private MyType MyType => myType.Value;
Then you can write: this.MyType everywhere rather than this.mytype.Value and encapsulate the fact that it is lazily instantiated in a single place.
One thing that's a shame is that C# doesn't support scoping the backing field to the property (i.e. declaring it inside the property definition) to hide it completely and ensure that it can only ever be accessed via the property.

The only one usage that I can think of
private bool IsPasswordSet
{
get
{
return !String.IsNullOrEmpty(_password);
}
}

Properties and fields are not one to one. A property is about the interface of a class (whether talking about its public or internal interface), while a field is about the class's implementation. Properties should not be seen as a way to just expose fields, they should be seen as a way to expose the intent and purpose of the class.
Just like you use properties to present a contract to your consumers on what constitutes your class, you can also present a contract to yourself for very similar reasons. So yes, I do use private properties when it makes sense. Sometimes a private property can hide away implementation details like lazy loading, the fact that a property is really a conglomeration of several fields and aspects, or that a property needs to be virtually instantiated with each call (think DateTime.Now). There are definitely times when it makes sense to enforce this even on yourself in the backend of the class.

I use them in serialization, with things like DataContractSerializer or protobuf-net which support this usage (XmlSerializer doesn't). It is useful if you need to simplify an object as part of serialization:
public SomeComplexType SomeProp { get;set;}
[DataMember(Order=1)]
private int SomePropProxy {
get { return SomeProp.ToInt32(); }
set { SomeProp = SomeComplexType.FromInt32(value); }
}

I use private properties to reduce code for accessing sub properties which often to use.
private double MonitorResolution
{
get { return this.Computer.Accesories.Monitor.Settings.Resolution; }
}
It is useful if there are many sub properties.

One thing I do all the time is store "global" variables/cache into HttpContext.Current
private static string SomeValue{
get{
if(HttpContext.Current.Items["MyClass:SomeValue"]==null){
HttpContext.Current.Items["MyClass:SomeValue"]="";
}
return HttpContext.Current.Items["MyClass:SomeValue"];
}
set{
HttpContext.Current.Items["MyClass:SomeValue"]=value;
}
}

I use them every now and then. They can make it easier to debug things when you can easily put in a breakpoint in the property or you can add a logging statement etc.
Can be also be useful if you later need to change the type of your data in some way or if you need to use reflection.

I know this question is very old but the information below was not in any of the current answers.
I can't imagine when I would ever need to be able to internally get but not set
If you are injecting your dependencies you may well want to have a Getter on a Property and not a setter as this would denote a readonly Property. In other words the Property can only be set in the constructor and cannot be changed by any other code within the class.
Also Visual Studio Professional will give information about a Property and not a field making it easier to see what your field is being used.

It is a common practice to only modify members with get/set methods, even private ones. Now, the logic behind this is so you know your get/set always behave in a particular way (for instance, firing off events) which doesn't seem to make sense since those won't be included in the property scheme... but old habits die hard.

It makes perfect sense when there is logic associated with the property set or get (think lazy initialization) and the property is used in a few places in the class.
If it's just a straight backing field? Nothing comes to mind as a good reason.

Well, as no one mentioned you can use it to validate data or to lock variables.
Validation
string _password;
string Password
{
get { return _password; }
set
{
// Validation logic.
if (value.Length < 8)
{
throw new Exception("Password too short!");
}
_password = value;
}
}
Locking
object _lock = new object();
object _lockedReference;
object LockedReference
{
get
{
lock (_lock)
{
return _lockedReference;
}
}
set
{
lock (_lock)
{
_lockedReference = value;
}
}
}
Note: When locking a reference you do not lock access to members of the referenced object.
Lazy reference: When lazy loading you may end up needing to do it async for which nowadays there is AsyncLazy. If you are on older versions than of the Visual Studio SDK 2015 or not using it you can also use AsyncEx's AsyncLazy.

One more usage would be to do some extra operations when setting value.
It happens in WPF in my case, when I display some info based on private object (which doesn't implement INotifyPropertyChanged):
private MyAggregateClass _mac;
private MyAggregateClass Mac
{
get => _mac;
set
{
if(value == _mac) return;
_mac = value;
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(DisplayInfo)));
}
}
public string DisplayInfo => _mac.SomeStringInformationToDisplayOnUI;
One could also have some private method, such as
private void SetMac(MyAggregateClass newValue)
to do that.

Some more exotic uses of explicit fields include:
you need to use ref or out with the value - perhaps because it is an Interlocked counter
it is intended to represent fundamental layout for example on a struct with explicit layout (perhaps to map to a C++ dump, or unsafe code)
historically the type has been used with BinaryFormatter with automatic field handling (changing to auto-props changes the names and thus breaks the serializer)

Various answers have mentioned using properties to implement a lazy member. And this answer discussed using properties to make live aliases. I just wanted to point out that those two concepts sometimes go together.
When using a property to make an alias of another object's public property, the laziness of that property is preserved:
[DebuggerBrowsable(DebuggerBrowsableState.Never)]
private IDbConnection Conn => foo.bar.LazyDbConnection;
On the other hand, retrieving that property in the constructor would negate the lazy aspect:
Conn = foo.bar.LazyDbConnection;

Looking into the guideline (Properties (C# Programming Guide)) it seems no one expects to use properties as private members.
Properties enable a class to expose a public way of getting and setting values, while hiding implementation or verification code.
In any case it can be interchanged by one or two methods and vice versa.
So the reason can be to spare parentheses on getting and get field syntax on setting.

When should we use private variables and when should we use properties. Do Backing Fields should be used in same class?

In most of the cases we usually creates a private variable and its corresponding public properties and uses them for performing our functionalities.
Everyone has different approach like some people uses properties every where and some uses private variables within a same class as they are private and opens it to be used by external environment by using properties.
Suppose I takes a scenario say insertion in a database.
I creates some parameters that need to be initialized.
I creates 10 private variables and their corresp public properties
which are given as
private string name;
public string Name
{
get{return name;}
set{name=value;}
}
and so on. In these cases mentioned above, what should be used internal variables or properties.
And in those cases like
public string Name
{
get{return name;}
set{name=value>5?5:0;} //or any action can be done. this is just an eg.
}
In such cases what should be done.
What is the conclusion
I actually meant to ask this.
Should we use variables within that class or not or should we use properties everywhere within same class as well.

If you use auto-implemented properties, then the field will be hidden, so you are forced to use the property, even in the class where the property is defined. Auto-implemented properties are a good idea, unless you need to add some logic to the getter/setter.

If the only use for the private variable is as a storage container, you might use:
public string Name {get; set;}
IMHO one should never make variables public - always use properties so you can add constraints or change behaviours later on whitout changing the interface.

Made things more readable:
I expose my data always through properties.
If I do not need additional logic (e.g. validation) I use implicit properties. This way there is no backing field and I cannot access it by accident. If I need to add some additional logic I can easily change the implicit property to a "traditional" one. As I use the property everywhere I do not have to worry that my extra logic is not called.
If I need something extra (like validation) then I have a private backing field, but I access this field only in the property body (get/set accessors). Again I do not need to worry if I change something in the property: My code will always use the same logic.
The only reason for not calling the property in my opinion would be if for some reason I really do not want any additional logic to be called, but this seems a dangerous thing so I rather avoid it...

I never expose public variables. Why? Because I can't lay constraints on them, whereas I can when I'm using properties. I can first check the value if it meets my constraints (e.g. an email address) and then I save it. Otherwise I throw an Exception.

You should never expose public variables without a very good reason. It is tough to say never, because if you trying to interop with comm type components you might be required too.
Anything publicly exposed should be a property. Why is that?
The reason is if you need to change the source of the value, or add some business logic checking if it is a public member you are going to require anything using the code to change. If it is a property you can change the internal logic and not require anybody using it to change the code.
I personally use properties and only create members variables when I want a property to do more than getting or setting (since this is easy with C# 3.0 with shortcut properties).
If I want to keep a property from being publicly exposed I make it as private, and only expose it when I have too.

We require explicit private variables in some situation like validation before set.Sometime we also need to conversion of input, for instance , formatting the input.