Since C# 3.0 there is the new syntax to autogenerate the instance variable from a propertie:
public string Foo { get; set; }
But there is no way to access the underlying backing field. So I don't really see the point of it because declaring the same instance variable would produce the same effect without the overhead of calling the "getter" and "setter".
public string Foo;
Declaring the property like:
public string Foo { get; }
or
public string Foo { set; }
is totally useless since we are not able to write resp. read the content of the field.
Does someone have a good explanation for why in C# they have put all this effort to introduce this syntactic sugar?
EDIT: People seems to think that I am confusing field and properties so let me clarify what I have said.
If you are using a property with auto generate field:
public string Foo { get; set; }
Then there is no point to it, since whenever you access the properties there is the overhead call to the get_Foo() "getter" every time you are accessing the properties and since your aren't doing anything particular in the the "getter" there is not mush interest of creating this property. Creating the field would have been exactly the same and it is mush faster (optimization wise).
Thanks
public string Foo { get; set; } defines a property.
public string Foo; defines a field.
They are different things. And the former is very convenient when you actually want a property and not a field.
As for accessing, you can define different access levels:
public string Foo { get; private set; }
See also Difference between Property and Field in C# 3.0+
As for your edit, what you are saying only makes sense if:
You are 100% sure that your property accessors will never contain any actual logic.
You are 100% sure that your field will never be data bound.
If any of the above is not true, then you need to define a property, even if that property seems like an empty stub.
Then, when later you decide to add logic to the accessors, you will not break all those clients that rely on your field being a field.
And if your class may be data bound, you need a property right away, as the data binding mechanisms ignore fields.
public string Foo;
Is a field.
public string Foo { get; set; }
Is a propery. They aren't the same thing, which has been discussed before. One of the mainly propagated advantages is the access control: get; private set; is used quite often as an example.
But there is no way to access the underlying backing field.
Yes there is, by calling the getter. Use [this.]Propertyname when you want to access it locally.
public string Foo { get; }
and
public string Foo { set; }
Will give you compiler errors, since you have to implement both get and set.
By itself it's pointless, but you can do things like this:
public string Foo { private set; get; }
Which has a lot more value.
Also properties and fields are not the same things.
The point of it is to make the code more concise and give you less to type.
In your example:
public string Foo;
Is a field and isn't the same as a property:
public string Foo { get; set; }
So the auto-property syntax has a use and is somewhat equivalent to:
private string _foo;
public string Foo { get { return _foo; } set { _foo = value; } }
However it doesn't create nice names, it uses safe names that would be invalid in C# (but are valid in IL).
Property overhead, though technically possible, is usually ironed out by the JIT into direct field access.
Properties are also usually the target for most data-binding frameworks. In reflection, a property differs from a field. WPF / WinForms data binding uses properties (not public fields). Most properties use a backing field to store the data. The trade-off is that when in the class, you use the property still as opposed to using the backing field. In practice, on release-optimized code, the performance is exactly the same as the JIT resolves them into exactly the same thing.
It makes defining properties faster and the code cleaner. If you don't need a property then don't define one - but I would recommend against public fields. You can make the property private and accessing it doesn't do anything more than returning the IL defined field. Further, if you need to do some work in the get or set then you'll have to define a backing value somehow, whether that be a field or some inherited member.
Related
I have been coding classes like this:
public class ReportViewModel
{
public string Status;
public string DataSource;
public String DataStore { get; set; }
public PageMeta PageMeta { get; set; }
public ICollection<Question> List { get; set; }
}
Note that most of the fields use { get; set; } except the first two which I let Visual Studio add for me.
What I am wondering is do I really need to use { get; set; }. It seems to me that VS2010 does not automatically add this so do I need it?
You've created a class with two public fields (Status and DataSource) and three public properties (DataStore, PageMeta and List). I would advise against having public fields - and you should actually consider whether you really need all of these to be mutable properties at all.
There are various advantages to using properties over public fields, but the main one in my mind is that a property is logically part of the API of a class, whereas a field is logically an implementation detail. The property says what callers can do - a field says how a value is stored.
{ get; set; } indicate autoimplemented properties. In .NET there is a difference between properties and fields. Normally fields should be private. They are used for some specific implementation and should in most cases be internal to the class. Properties on the other hand are used to encapsulate behavior that is exposed to the consumers.
If you want them properly exposed as properties, yes.
They are different: your first two members are fields - not properties. The others are properties with auto-implemented accessors.
When you don't add the get and set you are using a field rather than a property. Which in many cases won't make a lot of difference. However, you can't databind to a field like you can with a Property. So you would lose that.
At all depends on how this class will be used.
If this is in your code, just used in your current product, then there isn't really much difference between fields (no {get;set;}) and properties (with the {get;set;}).
However in that case they probably shouldn't be public, make them internal or private instead so that it's clear that external code shouldn't use them.
If your class is going to be used by other assemblies then you should always convert public fields to properties.
The reason is that if you want to extend properties later on (i.e. add a body to the set) then your users can just get the new DLL from you. However if you've used fields then converting them to a property will look the same in the IDE, but require your users to recompile when they get the altered DLL.
Being public tells consumers that they can rely on that member being present, being a property gives you more control of how you deliver it to them.
There is a difference. The first two are fields and the remainder are auto-properties.
The second one, the compiler generates a private backing field and some boiler-plate get/set methods. These then allow you to access the properties like they were fields, but with the advantages only available to properties.
It is always recommended to hide fields behind properties, by either making them private and writing your own property around it or using an auto-property.
There's some advantages to properties. One being that properties can be made read-only, or even write-only, or read-only with an internal write-only, etc. Since they act just like methods, you can execute any arbitrary code inside of them. This is useful for when you need to implement things like INotifyPropertyChanged or if the property is actually calculated from several fields behind it.
The other advantage is encapsulation. You aren't tying yourself directly to the fields of the class, but rather the property. So if some detail about the field changes (say it goes away and becomes calculated), by using the property you are insulating yourself from those implementation details.
You should certainly look at using properties (for now adding the { get; set; }) for all cases. They are good practice in that they provide a level of encapsulation that shields the user from implementation specific details.
You do not have to, but this just coding stundart, with its pros and cons.
Consider this link for more resources:
Property Acessors
I know that automatic properties must define a get and set accessor method, I also know that it is possible for either of these accessors to be made invisible by means of an access modifier.
Is there a technical reason why the compiler is happy with
public object Property { get; set; }
but not
public object Property { get; }
My (possibly wrong) understanding of this code is that the compiler generates a backing field that is hidden from the calling code like so:
private object hiddenField; //hidden by compiler.
public object Property
{
get { return hiddenField; }
set { hiddenField = value;}
}
If the compiler can generate that, is there a reason that it can't omit the set accessor function based on the presence (or lack thereof) of a setter in the property declaration.
I understand that this may be an issue of feature scope rather than a technical limitation, I also freely admit that I have not yet consulted the C# language specification as yet.
[UPDATE 2]
Forgive me...I'm an idiot :P, I see now, thank you everyone for tollerating my senior moment/
Without the set accessor, there is no way to set the value, since you don't have a way to access "hiddenField".
Similarly, without a get accessor, there would be no way to get back a value you set.
Since it really becomes useless, it's not allowed.
However, you can have different accessibility on the two methods:
public object Property { get; private set; }
This provides you the ability to hide the set from outside, but still have a usable property.
public object Property { get; private set; }
will work, and it will have the semantics you expect it to.
How could you use a property such the following?
public object Property { get; }
Theoritically if you could write something like that it always returns null as it lacks to the set accessor. I think it is useless unless you set the hidden field in some way to have a static value to always return it.
From the C# spec:
Because the backing field is
inaccessible, it can be read and
written only through the property
accessors, even within the containing
type.
Leaving one of the accessors out would mean that the property would either be read-only or write-only, even within the constructor of the class/struct. Not very useful.
could someone explain me what's the idea behind using Auto-Implemented Properties c#?
public class Customer
{
public int ID { get; set; }
public string Name { get; set; }
}
I get the motivation to use properties for private field, so we can determine how one can access a private field. But here - it's just like defining the field to be public from the first place. no?
Is there a difference between defining a field to be "public const" or define it to have a get-only property ?
A public automatic property is not the same as a public field, they are not binary compatible. If you implement a public field and later on want to add some logic, you will have to change it into a property and thereby introduce a breaking change (because of the binary incompatibility). This is the reason why many conventions state that you should never expose public fields but rather use properties.
So, automatic properties are just a convenient starting point for any simple non-private class value member, allowing one to add logic later on while keeping binary compatibility.
Properties can be databound, whereas fields can not.
Automatically implemented properties are essentially syntactic sugar. Once compiled, the backing store exists. It just isn't available from the source code.
As others have stated, properties and fields are not equivalent. Fields and properties aren't compatible so changing between them is a breaking change. In addition, you cannot use data binding with fields.
Final point. Though in your case there's little functional difference between the example and a public field, you can change the visibility of one of the accessors. So, to create a read-only property using an automatic property, you may do something like:
public int ID { get; private set; }
In this case, the get accessor is public, as per the entire signature, but the set accessor is private.
I will let MSDN do the talking here....
"In C# 3.0 and later, auto-implemented properties make property-declaration more concise when no additional logic is required in the property accessors. They also enable client code to create objects. When you declare a property as shown in the following example (see MSDN article for example), the compiler creates a private, anonymous backing field that can only be accessed through the property's get and set accessors"
Probably the most advantageous difference is you can do pre/post validation, raise PropertyChanged events etc
Is there a difference between defining a field to be "public const" or define it to have a get-only property?
Yes, a get-only field must have a private field declaration. This field can be changed by the class internally, marking a field as const means it cannot be modified.
2: a public const has to be defined at compiletime, you cannot use reference objects for that. Only classes that inherit from System.ValueType (string, int, double, ...)
A const is also static whereas a property with only a getter is not (every class has it's own instance.)
Add logic to getter function. Can access values of another property
public string Status
{
get { return DeactivateDate != null ? "InActive" : "Active"; }
private set { }
}
Is there a difference between:
public T RequestedValue { get; set; }
and
public T RequestedValue;
?
Taken from this code:
public class PropertyChangeRequestEventArgs<T>:EventArgs
{
public PropertyChangeRequestEventArgs(T pRequestedValue)
{
RequestedValue = pRequestedValue;
}
public T RequestedValue { get; set; }
}
The first is an Auto-Implemented Property the second is a Field. Regular Properties expose Getters and Setters but have a private field to actually store the value:
private int someProperty;
public int SomeProperty
{
get { return someProperty; }
set { someProperty = value; }
}
The first allows you to change certain aspects of the implementation of your class without affecting all the other code in your application. The most important point is that, with properties, changes can be made without breaking binary compatibility (although a field can often be changed to a property without breaking code). If it is a public member, a property is advisable. (Stealing shamelessly from Snarfblam's comment)
From the Properties page:
Properties are members that provide a flexible mechanism to read, write, or compute the values of private fields. Properties can be used as if they are public data members, but they are actually special methods called accessors. This enables data to be accessed easily and still helps promote the safety and flexibility of methods.
Properties with a backing field are the most flexible form as they allow easy implementation of things like the INotifyPropertyChanged event for updating the UI in Model-View-ViewModel implementations.
deep explanation!
The {get; set;} is an automatic property, while the second is a field.
a field is a normal variable, from some type, that contains data.
a property is a couple of methods (well sometimes it's just one), one for get, and one for set. they only have a syntax like fields, but actually they are quite different.
properties are usually for filtering the set of the value, or virtualizing something in the get, etc.
automatic properties, also create a private field behind the scenes, return its value in the get, and set its value in the set.
seemingly this is just like a normal field, but behind the scenes (IL) using properties is totally different from using fields.
a.Property1 = 4;
is translate into something like:
a.Set_Propert1(4);
and this:
x = a.Property1;
is translate to something like this:
x = a.Get_Property1();
so why is it a good practice to use only public properties, even if they are automatic?
say you are writing a library, that is used by other application, and someday you want to release a new version of that library that constrains one of your class' fields..
if you are using properties, you can just change the property (even if it is an automatic one, you can replace it by a full one), and then any application which used your library can still use it in the same way.
but if you made a public field, which you now want to constrain, you'll need to make a property for this and make the field private, but if you will, any application that used you library will no more be bale to, because the way it use fields and property is different.
You may write:
public T RequestedValue { get; set; }
as a shortcut of:
private T _requestedValue;
public T RequestedValue
{
get { return this._requestedValue; }
set { this._requestedValue = value; }
}
They are totally equivalent, also considering the performance.
The answer is, yes you can remove the { get; set; } but then a whole load subtle differences kick in. Some will say fields and properties express radically different design intent but in practice this distinction has been eroded over the years as C# evolves and progressively blurs the the syntactic differences.
For a good list of compiler-binary level differences between fields and properties refer to SO question difference-between-property-and-field-in-c. But the answers to that question missed one significant point about the special role of properties when declaring interfaces.
In C#, if I declare an auto-implemented property, why do I have to declare BOTH the get and set part?
i.e.
public string ThisWorks { get; set; }
public string ThisDoesnt { get; }
Isn't this just syntactic sugar - i.e. the compiler inserts a private field for the property? So why the problem?
Curious.
If you didn't have a setter - then how would you ever set the property?
Incidentally, you can specify the accessibility, eg:
public string Foo
{
get;
private set;
}
Without a setter, you would never be able to provide a value - as you don't have any way of specifying the backing variable's name.
I've requested a readonly automatic property, declared like this:
public string ReadonlyProperty { get; readonly set; }
which would create a readonly backing variable, a property with only a getter, and translate all calls to the setter into direct access to the variable. You could only call the setter within the constructor - just like for normal readonly variables.
We'll see whether this request does any good... it's a real shame it's not in there at the moment, as it makes it harder to implement immutable types than mutable types :(
An auto-implemented property has no accessible private store, so you would have no way to set the value without a setter, making it totally useless.
You need a set - otherwise, how does your auto-implemented property get its value? When auto-implementing the property, you have to have a set accessor to at least give it a value during construction.
Interestingly, the new Roslyn compiler in Visual Studio 2015 now allows this, even if the project is configured to use C# version 5.