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This question already has answers here:
What is the difference between a field and a property?
(33 answers)
Closed 9 months ago.
Similar questions has been asked a lot but it still doesn't make sense to me as I am beginner.
here is the link
What is the { get; set; } syntax in C#?
As that answer states
(I will be using age instead of "name" to avoid confusion)
Case 1
public class Genre
{
public int Age { get; set; }
}
and
Case 2:
public class Genre
{
private int age;
public int Age
{
get
{
return this.age;
}
set
{
this.age = value;
}
}
}
Both are the same things.
So for Case 1, where is private age variable?
Does it get declared in the backend.
If Yes, then what name will be assign to it?
Surely not (Age => age) Right?
It feels like,
public int Age { get; set; }
// is same thing as
public int Age;
Now, people have mentioned that one is property another is field. But they both can be used in similar way. So what is the difference on application level?
Can you please give me an example?
It feels like,
public int Age { get; set; }
is same thing as
public int Age;
Absolutely not, the first one is two functions, the setter and the getter, while the second one is a field, an integer. As a physical example of the difference, you can do ref Age in the second example, since it has a physical location in memory, but not in the first example, since it's just functions, it's code.
So for Case 1, where is private age variable? Does it get declared in the backend. If Yes, then what name will be assign to it?
Yeah, it gets generated for you by the compiler with a name you can't declare in C# because it contains invalid characters (that are valid in .Net in general). The actual name doesn't matter, just know that you can't possibly use it or collide with it.
The main difference between the two members in your last code snippet is encapsulation
See the "Encapsulation" part on this page:
https://learn.microsoft.com/en-us/dotnet/csharp/fundamentals/tutorials/oop
Hiding the internal state and functionality of an object and only allowing access through a public set of functions.
You asked about what private field gets generated if you use an automatic property. In fact the compiler will generate a private backing field usually called something like k__BackingField or similar.
For example, I created a basic class as follows:
public class Dog
{
public string Name { get; set; }
}
This definitely creates a field in the background, and I can find out by using ILSpy to decompile it and we see the following:
Notice the Name property is there as you'd expect, with its getter and setter. But notice also the k__BackingField.
When we inspect it, it is comprised of the following code:
[CompilerGenerated]
[DebuggerBrowsable(DebuggerBrowsableState.Never)]
private string <Name>k__BackingField;
So we can see that there is definitely a private field in the background being generated for the property. We can also confirm that it actually uses that field by inspecting the get_Name getter on the Name property:
[CompilerGenerated]
{
return <Name>k__BackingField;
}
The getter for the Name property indeed returns the private field that was compiler generated for us.
I think what you're stuck on is why we would do this. Basically, if you simply have a public field on a class, you're giving permission for all-and-any other classes to set and get that field without any kind of checks or balances or rules about what goes on when setting or retrieving that value. For small applications that aren't very complex, this won't create an issue for you. But in the future when you're writing bigger applications or libraries, when you want to guarantee certain functionality behaves the same way all the time, this best practice will be necessary.
There is no difference when you use them as simple variables but using a variable as property gives you the ability to perform a check or create an event handler. For example:
private int _onetoten;
public int OneToTen
{
get => _onetoten;
set
{
if ((value > 0) && (value < 11))
{
_onetoten = value;
}
}
}
Can someone tell me, what is the porpose of using a public property for a private class member but not implementing anything in the set and get part? I know that it could be just for examples and that later on you can implement something but I don't know if there is any meaning using it like that
I am going to assume you know there is a private field generated by the C# compiler as the field backing up this property. It is syntactic sugar. I am also going to assume you know this is an auto-implemented property. So what is the point of a property if it public with no logic in the get or set. In other words, any class can access it and set its value. So why choose this property over a public field?
Purpose of it is:
Today the get and set is empty but it may need code in the future. To avoid breaking a contract in the future, you use an empty get and set.
Most .NET databinding can be done against properties but not fields. So although it is empty, it still serves a far greater purpose.
The get and set can have access modifiers. For example, you can say set is private but get is public.
A field cannot be used in interfaces but properties can.
This is an "auto-implemented" property in C#. In effect, the property acts as a full property, i.e.:
This:
public int Number { get; set; }
Is equivalent to:
private int _number;
public int Number
{
get
{
return this._number;
}
set
{
this._number = value;
}
}
This prevents you from having to type out the full property declaration. This is useful when you don't have any additional logic in the getter and/or setter.
If you're creating simple data mapping and transfer classes, auto-implementing properties can make the class definition far more concise.
When you see
public int Count { get; set; }
as a member of a class, that is not nothing. You're just deferring to the default implementation of auto-properties. It's roughly,
private int _count;
public int get__Count()
{
return _count;
}
public void set__Count(int value)
{
_count = value;
}
You just have syntactic sugar in C# to use these methods roughly like a field, i.e.
instanceOfObject.Count = 42; // Not a field access, but behind the scenes a method call.
This question already has answers here:
Should I use public properties and private fields or public fields for data?
(13 answers)
Closed 7 years ago.
Just want to make sure.
public class Product
{
private decimal unitPrice;
public int Id { get; set; }
public string Code { get; set; }
public string Name { get; set; }
//private string code;
public decimal Unitprice
{
get
{
return unitPrice;
}
set
{
if (value >=0)
unitPrice = value;
}
}
}
Why we would have to make private variable to unitPrice to return the value to UnitPrice, does it written for some reasons ?
You dont make it private just to return the value for it. private is one of the access modifier here. They are used to limit the scope of the access/usage of that particular variable in your code.
private here means that unitPrice is currently accessible or can be used by this particular class only. No other outside assembly can use this variable.
If you want to access a variable outside in other areas, you can opt to make it public.
Hope this clears it.
From design perspective the unit price property is exactly the same as the other properties but because there is a constraint on it.
if (value >=0)
only positive prices are valid, you have no other option than to foresee a private variable whereon the property is based.
In earlier versions of .NET we could not do something like this :
public int Id { get; set; }
And had to write it out in full all the time. The notation above is more handy and it makes the code clearer too. It used to be like this :
private int _id;
public int Id{
get{ return _id;}
set{ _id = value;}
}
Yes, get and set properties are useful when you want to have some control over variable. Consider the following case.
If you specify the variable as private you want no one to be able to access your variable.
But if you want others to be able to access your private variable but you dont want others to change it. In this case you can use Properties
public class Product
{
private decimal price;
public decimal Price{get{ return price;}}
}
now others have access to the price but they cant change it
In your case you are allowing others both to get and set your unitprice, which is equal to giving unitprice public access. However you are allowing on one condition that the unitprice should be set to 0. So C# properties are perfect match for this scenario.
Hope this helps!!
The public property UnitPrice is exposed to other classes to be read or modified. But being a property allows your class a degree of control over the value - you can validate any change for instance. Also, internally you can completely change how the value is obtained and modified without changing the contract of the class. So in other words, you would be able to make such changes without affect any consumers.
The backing field unitPrice is purely an implementation detail, it is internal state that is encapsulated by the class. Exposing this field means you lose any and all chance to modify the derivation of the value and you have no entry point for validating changes to the value. Properties may seem pointless abstraction at first but they will help make your code more maintainable as changes can be more easily confined to single classes.
The get and set blocks are purely syntactic sugar and under the covers the compiler creates two methods called get_UnitPrice() and set_UnitPrice(x) that are used for read/write operations on the property. You could just use similar methods but properties are more readable and designed to be a low cost way of interacting with class state and methods are for providing behaviour.
Sometimes you have a private field that backs a property, you only ever want to set the field via the property setter so that additional processing can be done whenever the field changes. The problem is that it's still easy to accidentally bypass the property setter from within other methods of the same class and not notice that you've done so. Is there a way in C# to work around this or a general design principle to avoid it?
IMHO, it is not used, because:
The class must trust itself
If your class gets as large that one part does not know the other, it should be divided.
If the logic behind the property is slightly more complex, consider to encapsulate it in an own type.
I'd consider this a nasty hack and try to avoid it if possible, but...
You can mark the backing field as obsolete so that the compiler will generate a warning when you try to access it, and then suppress that warning for the property getter/setter.
The warning codes that you'd need to suppress are CS0612 for the plain Obsolete attribute and CS0618 if the attribute has a custom message.
[Obsolete("Please don't touch the backing field!")]
private int _backingField;
public int YourProperty
{
#pragma warning disable 612, 618
get { return _backingField; }
set { _backingField = value; }
#pragma warning restore 612, 618
}
There's no inbuilt way to do what you want to do, but by the sounds of things you need another layer of abstraction between your class and that value.
Create a separate class and put the item in there, then your outer class contains the new class, and you can only access it through its properties.
No, there isn't. I'd quite like this myself - something along the lines of:
public string Name
{
private string name; // Only accessible within the property
get { return name; /* Extra processing here */ }
set { name = value; /* Extra processing here */ }
}
I think I first suggested this about 5 years ago on the C# newsgroups... I don't expect to ever see it happen though.
There are various wrinkles to consider around serialization etc, but I still think it would be nice. I'd rather have automatically implemented readonly properties first though...
You CAN do this, by using a closure over a local in the constructor (or other initialisation function). But it requires significantly more work that the helper class approach.
class MyClass {
private Func<Foo> reallyPrivateFieldGetter;
private Action<Foo> reallyPrivateFieldSetter;
private Foo ReallyPrivateBackingFieldProperty {
get { return reallyPrivateFieldGetter(); }
set { reallyPrivateFieldSetter(value); }
}
public MyClass() {
Foo reallyPrivateField = 0;
reallyPrivateFieldGetter = () => { return reallyPrivateField; }
reallyPrivateFieldSetter = v => { reallyPrivateField = v; };
}
}
I suspect that the underlying field type Foo will need to be a reference class, so the two closures are created over the same object.
There is no such provisioning in C#.
However I would name private variables differently (e.g. m_something or just _something) so it is easier to spot it when it is used.
You can put all of your private fields into a nested class and expose them via public properties. Then within your class, you instantiate that nested class and use it. This way those private fields are not accessible as they would have been if they were part of your main class.
public class A
{
class FieldsForA
{
private int number;
public int Number
{
get
{
//TODO: Extra logic.
return number;
}
set
{
//TODO: Extra logic.
number = value;
}
}
}
FieldsForA fields = new FieldsForA();
public int Number
{
get{ return fields.Number;}
set{ fields.Number = value;}
}
}
It just provides a level of obstruction. The underlying problem of accessing private backing fields is still there within the nested class. However, the code within class A can't access those private fields of nested class FieldForA. It has to go through the public properties.
Perhaps a property backing store, similar to the way WPF stores properties?
So, you could have:
Dictionary<string,object> mPropertyBackingStore = new Dictionary<string,object> ();
public PropertyThing MyPropertyThing
{
get { return mPropertyBackingStore["MyPropertyThing"] as PropertyThing; }
set { mPropertyBackingStore["MyPropertyThing"] = value; }
}
You can do all the pre-processing you want now, safe in the knowledge that if anyone did access the variable directly, it would have been really really hard compared to the property accessor.
P.S. You may even be able to use the dependency property infrastructure from WPF...
P.P.S. This is obviously going to incur the cost of casting, but it depends on your needs - if performance is critical, perhaps this isn't the solution for you.
P.P.P.S Don't forget to initialise the backing store! (;
EDIT:
In fact, if you change the value property stored to a property storage object (using the Command pattern for example), you could do your processing in the command object...just a thought.
Can't do this in standard C#, however you could
define a custom attribute say OnlyAccessFromProperty
write your code like
[OnlyAccessFromProperty(Name)]
String name
Name
{
get{return name;}
}
etc …
Then write a custom rule for FxCop (or another checker)
Add FxCop to your build system so if your custom rule find an error the build is failed.
Do we need a set of standard custom rules/attributes to enforce common design patens like this without the need to extend C#
C# has no language feature for this. However, you can rely on naming conventions, similar to languages which have no private properties at all. Prefix your more private variable names with _p_, and you'll be pretty sure that you don't type it accidentally.
I don't know C# but in Java you may have a base class with only private instance variables and public setters and getters (should return a copy of the instance var.) and do all other in an inherited class.
A "general design principle" would be "use inheritance".
There is no build in solution in C#, but I think your problem can be solved by good OO design:
Each class should have a single purpose. So try to extract the logic around your field into a class as small as possible. This reduces the code where you can access the field by accident. If you do such errors by accident, your class is probably to big.
Often interface are good to restrict access to only a certain "subset" of an object. If that's appropriate for your case depends on your setting of course. More details about the work to be done would help to provide a better answer.
You say that you do additional processing. Presumably this would be detectable under the correct conditions. My solution, then, would be to create unit tests that implement conditions such that if the backing field is used directly the test will fail. Using these tests you should be able to ensure that your code correctly uses the property interface as long as the tests pass.
This has the benefit that you don't need to compromise your design. You get the safety of the unit tests to ensure that you don't accidently make breaking changes and you capture the understanding of how the class works so that others who come along later can read your tests as "documentation."
Wrap it in a class? The property thing is a bit like that anyway, associating data with methods - the "Encapsulation" they used to rave about...
class MyInt
{
private int n;
public static implicit operator MyInt(int v) // Set
{
MyInt tmp = new MyInt();
tmp.n = v;
return tmp;
}
public static implicit operator int(MyInt v) // Get
{
return v.n;
}
}
class MyClass
{
private MyInt myint;
public void func()
{
myint = 5;
myint.n = 2; // Can't do this.
myint = myint + 5 * 4; // Works just like an int.
}
}
I'm sure I'm missing something? It seems too normal...
BTW I do like the closures one, superbly mad.
My favorite solution to this (and what I follow) is to name private backing fields that are never intended to be used directly with a leading underscore, and private fields that are intended to be used without the underscore (but still lowercase).
I hate typing the underscore, so if I ever start to access a variable that starts with the underscore, I know somethings wrong - I'm not supposed to be directly accessing that variable. Obviously, this approach still doesn't ultimately stop you from accessing that field, but as you can see from the other answers, any approach that does is a work around and/or hardly practical.
Another benefit of using the underscore notation is that when you use the dropdown box to browse your class, it puts all of your private, never-to-be-used backing fields all in one place at the top of the list, instead of allowing them to be mixed in with their respective properties.
As a design practice, you could use a naming convention for "private properties" that's different from normal public members - for instance, using m_ItemName for private items instead of ItemName for public ones.
If you're using the C# 3.0 compiler you can define properties which have compiler-generated backing fields like this:
public int MyInt { get; set; }
That will mean there is only one way to access the property, sure it doesn't mean you can only access the field but it does mean that there's nothing but the property to access.
I agree with the general rule that the class should trust itself (and by inference anybody coding within the class).
It is a shame that the field is exposed via intellisense.
Sadly placing [EditorBrowsable(EditorBrowsableState.Never)] does not work within that class (or indeed the assembly(1))
In Visual C#, EditorBrowsableAttribute does not suppress members from a class in the same assembly.
If you really do wish to solve this aspect of it the the following class may be useful and makes the intent clear as well.
public sealed class TriggerField<T>
{
private T data;
///<summary>raised *after* the value changes, (old, new)</summary>
public event Action<T,T> OnSet;
public TriggerField() { }
///<summary>the initial value does NOT trigger the onSet</summary>
public TriggerField(T initial) { this.data=initial; }
public TriggerField(Action<T,T> onSet) { this.OnSet += onSet; }
///<summary>the initial value does NOT trigger the onSet</summary>
public TriggerField(Action<T,T> onSet, T initial) : this(onSet)
{
this.data=initial;
}
public T Value
{
get { return this.data;}
set
{
var old = this.data;
this.data = value;
if (this.OnSet != null)
this.OnSet(old, value);
}
}
}
Allowing you to (somewhat verbosely) use it like so:
public class Foo
{
private readonly TriggerField<string> flibble = new TriggerField<string>();
private int versionCount = 0;
public Foo()
{
flibble.OnSet += (old,current) => this.versionCount++;
}
public string Flibble
{
get { return this.flibble.Value; }
set { this.flibble.Value = value; }
}
}
alternatively you can go for a less verbose option but accessing Flibble is by the not idiomatic bar.Flibble.Value = "x"; which would be problematic in reflective scenarios
public class Bar
{
public readonly TriggerField<string> Flibble;
private int versionCount = 0;
public Bar()
{
Flibble = new TriggerField<string>((old,current) => this.versionCount++);
}
}
or solution if you look at the community content!
The new Lazy class in .net 4.0
provides support for several common
patterns of lazy initialization
In my experience this is the most common reason I wish to wrap a field in a private properly, so solves a common case nicely. (If you are not using .Net 4 yet you can just create your own “Lazy” class with the same API as the .Net 4 version.)
See this and this and this for details of using the Lazy class.
Use the "veryprivate" construct type
Example:
veryprivate void YourMethod()
{
// code here
}
In much of the code I have seen (on SO, thecodeproject.com and I tend to do this in my own code), I have seen public properties being created for every single private field that a class contains, even if they are the most basic type of get; set; like:
private int myInt;
public int MyInt
{
get { return myInt; }
set { myInt = value }
}
My question is: how does this differ from:
public int MyInt;
and if we should use properties instead of public fields why should we use them in this specific case? (I am not talking about more complex examples where the getters and setters actually do something special or there is only one get or set (read/write only) rather than just returning/setting a value of a private field). It does not seem to add any extra encapsulation, only give a nice icon in IntelliSense and be placed in a special section in class diagrams!
See this article http://blog.codinghorror.com/properties-vs-public-variables/
Specifically
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.
Three reasons:
You cannot override fields in subclasses like you can properties.
You may eventually need a more complex getter or setter, but if it's a field, changing it would break the API.
Convention. That's just the way it's done.
I'm sure there are more reasons that I'm just not thinking of.
In .Net 3.x you can use automatic properties like this:
public int Age { get; set; }
instead of the old school way with declaring your private fields yourself like this:
private int age;
public int Age
{
get { return age; }
set { age = value; }
}
This makes it as simple as creating a field, but without the breaking change issue (among other things).
When you create private field name and a simple public property Name that actually gets and sets the name field value
public string Name
{
get { return name; }
}
and you use this property everywhere outside your class and some day you decide that the Name property of this class will actually refer to the lastName field (or that you want to return a string "My name: "+name), you simply change the code inside the property:
public string Name
{
get { return lastName; //return "My name: "+name; }
}
If you were using public field name everywhere in the outside code then you would have to change name to lastName everywhere you used it.
Well it does make a difference. Public data can be changed without the object instance knowing about it. Using getters and setters the object is always aware that a change has been made.
Remember that encapsulating the data is only the first step towards a better structured design, it's not an end-goal in itself.
You have to use properties in the following cases:
When you need to serialize data in the property to some format.
When you need to override properties in derived class.
When you implement get and set methods with some logic. For example, when you implement Singleton pattern.
When you're derived from interface, where property was declared.
When you have specific issues related to Reflection.
It... depends?
I always use getters & setters, since they created this shortcut:
public int Foo { get; set; }
At compile time it is translated. Now you can't get fancy with it, but it is there, and if you need to get fancy you just spell it out later.
However public, private, protected... it's all a matter of who you want to be able to tweak the data. We use inheritance a lot and this is a very common method for us, so that only chidren can edit certain properties.
protected _foo;
public Foo
{
get { return _foo; }
} //lack of set intentional.
I can't believe that with 11 answers, nobody has said this:
Not all private fields should be exposed as public properties. You should certainly use properties for anything that needs to be non-private, but you should keep as much of your class private as possible.
There are many reasons why.
Mainly:
You can do some other functions when the variable is set
You can prevent setting and provide only get
Some 'things' only work on properties (DataBinding, for example)
You can hide the implementation of the property [perhaps it is a ViewState variable, in ASP.NET).
The point is - what if further down the line you want to make sure that every time myInt is referenced something special happens (a log file is written to, it's changed to 42 etc)? You can't do that without getters and setters. Sometimes it's wise to program for what you might need, not what you need right now.
Actually, if you're using Silverlight, you'll realise that fields cannot be set a static resources and thus you'll have to use a property (even to access a const).
I've realised that when I tried to federate the region names I use in Composite Guidance (PRISM).
However, that's just a language limitations and apart from static/const fields I alsways use properties.
The idea is you should not accidentally/unintentionally change the value of a class private field outside.
When you use get and set, that means you are changing the class private field intentionally and knowingly.
Setting a value into a private field only changes that field,but making them in property you can handle another arguments for example,you can call a method after setting a value
private string _email;
public string Email
{
get
{
return this._email;
}
set
{
this._email = value;
ReplaceList(); //**
}
}
In simpler words, answer to your question is the access modifiers i.e. public and private.
If you use:
public int myInt;
public int MyInt
{
get { return myInt; }
set { myInt = value }
}
then both MyInt property and myInt variable is available in the project to be modified.
Means, if your class suppose A is inherited by class suppose B,
then myInt and MyInt both are available for modification and no check can be applied.
Suppose you want myInt value can be set in derive class if some particular condition pass.
This can be achieved only by making field private and property to be public.
So that only property is available and conditions can be set based on that.