I need to implement a read only property on my type. Moreover the value of this property is going to be set in the constructor and it is not going to be changed (I am writing a class that exposes custom routed UI commands for WPF but it does not matter).
I see two ways to do it:
class MyClass
{
public readonly object MyProperty = new object();
}
class MyClass
{
private readonly object my_property = new object();
public object MyProperty { get { return my_property; } }
}
With all these FxCop errors saying that I should not have public member variables, it seems that the second one is the right way to do it. Is this correct?
Is there any difference between a get only property and a read only member in this case?
The second way is the preferred option.
private readonly int MyVal = 5;
public int MyProp { get { return MyVal;} }
This will ensure that MyVal can only be assigned at initialization (it can also be set in a constructor).
As you had noted - this way you are not exposing an internal member, allowing you to change the internal implementation in the future.
C# 6.0 adds readonly auto properties
public object MyProperty { get; }
So when you don't need to support older compilers you can have a truly readonly property with code that's just as concise as a readonly field.
Versioning:
I think it doesn't make much difference if you are only interested in source compatibility.
Using a property is better for binary compatibility since you can replace it by a property which has a setter without breaking compiled code depending on your library.
Convention:
You are following the convention. In cases like this where the differences between the two possibilities are relatively minor following the convention is better. One case where it might come back to bite you is reflection based code. It might only accept properties and not fields, for example a property editor/viewer.
Serialization
Changing from field to property will probably break a lot of serializers. And AFAIK XmlSerializer does only serialize public properties and not public fields.
Using an Autoproperty
Another common Variation is using an autoproperty with a private setter. While this is short and a property it doesn't enforce the readonlyness. So I prefer the other ones.
Readonly field is selfdocumenting
There is one advantage of the field though:
It makes it clear at a glance at the public interface that it's actually immutable (barring reflection). Whereas in case of a property you can only see that you cannot change it, so you'd have to refer to the documentation or implementation.
But to be honest I use the first one quite often in application code since I'm lazy. In libraries I'm typically more thorough and follow the convention.
With the introduction of C# 6 (in VS 2015), you can now have get-only automatic properties, in which the implicit backing field is readonly (i.e. values can be assigned in the constructor but not elsewhere):
public string Name { get; }
public Customer(string name) // Constructor
{
Name = name;
}
private void SomeFunction()
{
Name = "Something Else"; // Compile-time error
}
And you can now also initialise properties (with or without a setter) inline:
public string Name { get; } = "Boris";
Referring back to the question, this gives you the advantages of option 2 (public member is a property, not a field) with the brevity of option 1.
Unfortunately, it doesn't provide a guarantee of immutability at the level of the public interface (as in #CodesInChaos's point about self-documentation), because to a consumer of the class, having no setter is indistinguishable from having a private setter.
In C# 9, Microsoft introduced a new way to have properties set only on initialization using the init accessor, like so:
public class Person
{
public string FirstName { get; init; }
public string LastName { get; init; }
}
This way, you can assign values when initializing a new object:
var person = new Person
{
Firstname = "John",
LastName = "Doe"
}
But later on, you cannot change it:
person.LastName = "Denver"; // throws a compiler error
You can do this:
public int Property { get { ... } private set { ... } }
I agree that the second way is preferable. The only real reason for that preference is the general preference that .NET classes not have public fields. However, if that field is readonly, I can't see how there would be any real objections other than a lack of consistency with other properties. The real difference between a readonly field and get-only property is that the readonly field provides a guarantee that its value will not change over the life of the object and a get-only property does not.
yet another way (my favorite), starting with C# 6
private readonly int MyVal = 5;
public int MyProp => MyVal;
https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/properties#expression-body-definitions
The second method is preferred because of the encapsulation. You can certainly have the readonly field be public, but that goes against C# idioms in which you have data access occur through properties and not fields.
The reasoning behind this is that the property defines a public interface and if the backing implementation to that property changes, you don't end up breaking the rest of the code because the implementation is hidden behind an interface.
Related
Update 1
It seems like either my English is terribly awful, or people just don't give a sh... to understand what I'm asking about or simply look at the title of the post.
C#5 specification clearly states:
Because the backing field is inaccessible, it can be read and written
only through the property accessors, even within the containing type.
This means that automatically implemented read-only or write-only
properties do not make sense, and are disallowed.
public string MyProperty {get;} has no sense, yet it costs nothing for compiler to emit getter not even warring about lacking setter. Backing field will be initialized with a default value. What does it mean? It means that designers spent some effort to implement a verification, to introduce functionality that could be left out.
Let's now consider C#6:
In C#6 the initialization of auto-implemented properties was introduced.
public string FirstName { get; set; } = "Jane";
or
public string FirstName { get; } = "Jane";
In the latter case property can be set in a constructor as well:
public class Program
{
public string ImagePath { get; }
public static void Main()
{
}
public Program()
{
ImagePath = "";
}
}
But only in constructor of the class where property was declared. Derived classes cannot set property's value.
Now ask yourself what this property means, if it was not initialized in constructor:
property string My {get;}
This is a 100% equivalent of C#5 prohibited property. It has no sense.
But such declaration being invalid in C#5 became valid in C#6. However semantics didn't change at all: this property is useless without explicit initialization.
That's why I am asking:
Why not explicitly initialized readonly auto-implemented property is valid in c# 6?
What I expect to see as an answer:
Either debunking of my initial assumptions about changes in C#6
Or the explanation of how and why compiler designers changed their mind
about what makes sense, and what does not.
I find the answer It's by design to be completely irrelevant. It is just a fact. I look for reasons. I don't believe compiler designers decide on changes in behavior of compiler with just tossing the coin.
This is an example of good answer.
Original question
In VS2015 this code is compiled without errors:
public class Program
{
public string ImagePath { get; }
public static void Main()
{
Console.WriteLine("Hello World");
}
}
However, in VS2013 I get error:
Compilation error (line 5, col 28): 'Program.ImagePath.get' must
declare a body because it is not marked abstract or extern.
Automatically implemented properties must define both get and set
accessors.
I know about initializable auto implemented properties, and in case of VS2015 field gets default value, that is null here. But then it's interesting to know why this snippet was invalid in C# 5?
Initializable auto-implemented readonly property left without explicit initialization seems to me a bit ODD. It is likely a mistake rather than intention. I'd personally prefer compiler to require explicit initialization in this case:
public string ImagePath { get; } = default(string);
Ok, I know that such property can be also assigned in constructor:
public class Program
{
public string ImagePath { get; }
public static void Main()
{
}
public Program()
{
ImagePath = "";
DoIt();
}
public void DoIt()
{
//ImagePath = "do it";
}
}
public class My : Program
{
public My()
{
//ImagePath = "asdasd";
}
}
But if compiler can check that local variable is not initialized, the same is possible for the property.
So why is it as it is?
The compiler is telling you that automatic properties must have both accessors defined. For example, you could fix the error with
public string ImagePath { get; private set; }
assuming that you do not intend the property to be settable outside the class.
As to why you have to declare a setter or manually implement the property -- well, what good would be a property that you can read from, but will always return the default value of its type since there is no way to set it? Conversely, what good would be a property you can write to but can neither read from nor hook into its setter?
C# 6.0 gives you the option of having write-once, read many auto-properties; this is a huge difference as the value can be arbitrarily chosen, allowing you convenient syntax for properties with immutable values.
I have no idea why your question have been down voted. This is interesting observation but please keep in mind that it is not a breaking change - it is just 'new functionality' that is 'leftover' of other functionality - initialization of auto-implemented properties.
That means it had no sense previously, but now it has.
Moreover, I think it has always had sense. E.g. when you have some base class or interface, for example
interface IPerson
{
int Age { get; }
}
Some day you may want to implement null-object pattern where the age is irrelevant. In c#5 you have to write public int Age { get { return 0; } }, while in c#6 you can simply do public int Age { get; } or even transform interface to abstract class changing only its definition from interface to abstract class.
I'm taking a C# class right now and I'm trying to find out the best way of doing things. I come from a Java background and so I'm only familiar with Java best-practices; I'm a C# novice!
In Java if I have a private property, I do this;
private String name;
public void setName(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
In C#, I see that there are many ways of doing this.
I can do it like Java:
private string name;
public void setName(string name) {
this.name = name;
}
public string getName() {
return this.name;
}
Or I can do it this way:
private string name;
public string Name {
get { return name; }
set { name = value; }
}
Or:
public string Name { get; set; }
Which one should I use, and what are the caveats or subtleties involved with each approach? When creating classes, I am following general best-practices that I know from Java (especially reading Effective Java). So for example, I am favoring immutability (providing setters only when necessary). I'm just curious to see how these practices fit in with the various ways of providing setters and getters in C#; essentially, how would I translate best-practices from the Java world into C#?
EDIT
I was posting this as a comment to Jon Skeet's answer but then it got long:
What about a non-trivial property (i.e., with significant processing and validation perhaps)? Could I still expose it via a public property but with the logic encapsulated in get and set? Why would/should I do this over having dedicated setter and getter methods (with associated processing and validation logic).
Pre-C# 6
I'd use the last of these, for a trivial property. Note that I'd call this a public property as both the getters and setters are public.
Immutability is a bit of a pain with automatically implemented properties - you can't write an auto-property which only has a getter; the closest you can come is:
public string Foo { get; private set; }
which isn't really immutable... just immutable outside your class. So you may wish to use a real read-only property instead:
private readonly string foo;
public string Foo { get { return foo; } }
You definitely don't want to write getName() and setName(). In some cases it makes sense to write Get/Set methods rather than using properties, particularly if they could be expensive and you wish to emphasize that. However, you'd want to follow the .NET naming convention of PascalCase for methods, and you wouldn't want a trivial property like this to be implemented with normal methods anyway - a property is much more idiomatic here.
C# 6
Hooray, we finally have proper read-only automatically implemented properties:
// This can only be assigned to within the constructor
public string Foo { get; }
Likewise for read-only properties which do need to do some work, you can use member-bodied properties:
public double Area => height * width;
If all you need is a variable to store some data:
public string Name { get; set; }
Want to make it appear read-only?
public string Name { get; private set; }
Or even better...
private readonly string _name;
...
public string Name { get { return _name; } }
Want to do some value checking before assigning the property?
public string Name
{
get { return m_name; }
set
{
if (value == null)
throw new ArgumentNullException("value");
m_name = value;
}
}
In general, the GetXyz() and SetXyz() are only used in certain cases, and you just have to use your gut on when it feels right. In general, I would say that I expect most get/set properties to not contain a lot of logic and have very few, if any, unexpected side effects. If reading a property value requires invoking a service or getting input from a user in order to build the object that I'm requesting, then I would wrap it into a method, and call it something like BuildXyz(), rather than GetXyz().
Use properties in C#, not get/set methods. They are there for your convenience and it is idiomatic.
As for your two C# examples, one is simply syntactic sugar for the other. Use the auto property if all you need is a simple wrapper around an instance variable, use the full version when you need to add logic in the getter and/or setter.
In C# favor properties for exposing private fields for get and/or set. The thie form you mention is an autoproperty where the get and set automatically generate a hidden pivot backing field for you.
I favor auto properties when possible but you should never do a set/get method pair in C#.
public string Name { get; set; }
This is simply a auto-implemented property, and is technically the same as a normal property. A backing field will be created when compiling.
All properties are eventually converted to functions, so the actual compiled implementation in the end is the same as you are used to in Java.
Use auto-implemented properties when you don't have to do specific operations on the backing field. Use a ordinary property otherwise. Use get and set functions when the operation has side effects or is computationally expensive, use properties otherwise.
Regardless of which way you choose in C# the end result is the same. You will get a backinng variable with separate getter and setter methods. By using properties you are following best practices and so it's a matter of how verbose you want to get.
Personally I would choose auto-properties, the last version: public string Name { get; set; }, since they take up the least amount of space. And you can always expand these in the future if you need add something like validation.
Whenever possible I prefer public string Name { get; set; } as it's terse and easily readable. However, there may be times when this one is necessary
private string name;
public string Name {
get { return name; }
set { name = value; }
}
In C# the preferred way is through properties rather than getX() and setX() methods. Also, note that C# does not require that properties have both a get and a set - you can have get-only properties and set-only properties.
public boolean MyProperty
{
get { return something; }
}
public boolean MyProperty
{
set { this.something = value; }
}
First let me try to explain what you wrote:
// private member -- not a property
private string name;
/// public method -- not a property
public void setName(string name) {
this.name = name;
}
/// public method -- not a property
public string getName() {
return this.name;
}
// yes it is property structure before .Net 3.0
private string name;
public string Name {
get { return name; }
set { name = value; }
}
This structure is also used nowadays but it is most suitable if you want to do some extra functionality, for instance when a value is set you can it to parse to capitalize it and save it in private member for alter internal use.
With .net framework 3.0
// this style is introduced, which is more common, and suppose to be best
public string Name { get; set; }
//You can more customize it
public string Name
{
get;
private set; // means value could be set internally, and accessed through out
}
Wish you better luck in C#
As mentioned, all of these approaches result in the same outcome. The most important thing is that you pick a convention and stick with it. I prefer using the last two property examples.
like most of the answers here, use Automatic properties. Intuitive, less lines of code and it is more clean. If you should serialize your class, mark the class [Serializable]/ with [DataConract] attribute. And if you are using [DataContract] mark the member with
[DataMember(Name="aMoreFriendlyName")]
public string Name { get; set; }
Private or public setter depends on your preference.
Also note that automatic properties require both getters and setters(public or private).
/*this is invalid*/
public string Name
{
get;
/* setter omitted to prove the point*/
}
Alternatively, if you only want get/set, create a backing field yourself
Which one should I use, and what are the caveats or subtleties involved with each approach?
When going with properties there is one caveat that has not been mentioned yet: With properties you cannot have any parametrization of your getters or setters.
For example imagine you want to retrieve a list items and want to also apply a filter at the same time. With a get-method you could write something like:
obj.getItems(filter);
In contrast, with a property you are forced to first return all items
obj.items
and then apply the filter in the next step or you have to add dedicated properties that expose items filtered by different criteria, which soon bloats your API:
obj.itemsFilteredByX
obj.itemsFilteredByY
What sometimes can be a nuisance is when you started with a property, e.g. obj.items and then later discovered that getter- or setter-parametrization is needed or would make things easier for the class-API user. You would now need to either rewrite your API and modify all those places in your code that access this property or find an alternative solution. In contrast, with a get-method, e.g. obj.getItems(), you can simply extend your method's signature to accept an optional "configuration" object e.g. obj.getItems(options) without having to rewrite all those places that call your method.
That being said, (auto-implemented) properties in C# are still very useful shortcuts (for the various reasons mentioned here) since most of the time parametrization may not be needed – but this caveat stands.
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.
Is there some internal difference between the C# syntactic sugar way of making properties:
public string FirstName { get; set; }
and just making public variables like this:
public string LastName;
I assume the first way is preferred and the second to be avoided. However, I often see this type of readonly property being used which is a form of the second type above:
public readonly string InternalCode;
Is this a best-practice way to create readonly property?
using System;
namespace TestProps
{
class Program
{
static void Main(string[] args)
{
Customer customer = new Customer();
customer.FirstName = "Jim";
customer.LastName = "Smith";
customer.Show();
}
}
class Customer
{
public string FirstName { get; set; } //prefered
public string LastName; //avoid
public readonly string InternalCode; //???
public Customer()
{
InternalCode = "234729834723984";
}
public void Show()
{
Console.WriteLine("{0}, {1} ({2})", LastName, FirstName, InternalCode);
Console.ReadLine();
}
}
}
Since he didn't answer (yet) and no one else referenced this yet: There is a great article on this topic by Jon Skeet amending his book C# in depth (give credits to Jon):
Why Properties Matter
Using a property provides an interface which is more resistant to change in the future. Let's say some time in the future, a decision is made to add a prefix to the internal code.
Using a public readonly variable exposes your internal structure and you will have a hard time adding the prefix to every line you used the internal variable of the class.
Using a Property, you can just write the following
public string InternalCode {
get { return _prefix + _internalCode; }
}
and you're done!
In my opinion, it's ok to expose public fields (especially if they're readonly or const). Having said that, I'd say that in the example you're presenting, I'd probably go with properties since they'll give you 2 advantages (over fields): 1) better encapsulation and may let you adapt your code in the future and 2) if you're doing data binding, then you do need the properties.
Yes. it is OK to have a public readonly variables (it is just that they can be initialized at the time of definition or constructor).
e.g. Decimal.MaxValue
Having public readonly property is good, if the backing value changes (other than what it was initialized with).
e.g. Environment.TickCount
I thought that Environment.NewLine will be a public readonly variable. Well, it is a public property (get only) and the reason could be to maintain compatibility across different platform.
Short answer: public const is ok, public readonly not necessarily, public get without set not neccessarily.
Objects that cannot be changed without being assigned can be ok. Reference types are dangerous as you can still change their values, even if you cannot change the reference itself.
The problem with the readonly keyword is that it does not mean what you'd understand as logically readonly/immutable. It means more like "can only be assigned in constructor". References cannot be changed, but its values can. There is no "real" readonly keyword provided by c#, unfortunately. See also https://blogs.msdn.microsoft.com/ericlippert/2007/11/13/immutability-in-c-part-one-kinds-of-immutability/
Properties cannot have the readonly keyword (https://titombo.wordpress.com/2012/11/11/using-the-c-modifiers/).
As others noted, you can use a property and only define get and no set, though you cannot set that property in the constructor. Using a private set, you can set the property from annywhere in the class, not only in the constructor. The readonly field would be a little more restrictive.