Can we have different access modifier for get and set in a property?
Yes, you can, however it is subject to the rule that your getter/setter cannot have a less restricted access modifier than the property itself.
For example (C#):
public Foo { get; private set; } //this is okay
protected Bar { get; public set; } //this will throw a compile error
You can restrict the getter or setter of a property:
public string MyProperty
{
get { return _myProperty; }
private set { _myProperty = value; }
}
It also works with internal and protected. However, the key word here is "restrict" - you can't make either modifier more accessible than the overall modifier.
Related
For proper encapsulation, should I use a private property with a manual getter method like in Java:
public class Foo {
private int Prop { get; set; }
public Foo
{
Prop = 1;
}
public int GetProp()
{
return Prop;
}
}
Or should I simply use a public property?
public class Foo {
public int Prop { get; private set; }
public Foo
{
Prop = 1;
}
}
Properties are the way of creating getters and setters in C#, so there is no reason to create a getter method, like you would in Java.
In other words: You should use the second example.
Typically the proper way to do this is:
private int prop;
public int Prop
{
get { return prop; }
set { prop = value; } //do other stuff within set if needed.
}
This way you have access to everything, but can still do something custom (commonly NotifyPropertyChanged) if needed.
A property is just a syntactic sugar for get_PropertyName and set_PropertyName methods in c#.
public class Foo
{
public int Prop { get; private set; }
}
Is equivalent to:
public class Foo
{
private int _prop;
private void set_prop(int value) { _prop = value; }
public int get_prop() { return _prop; }
}
It's best that you use auto properties when possible and use properties with backing fields when you need to add logic to the getter/setter of individual fields.
If the property is going to be private, as it is in your first example, you should just use a field.
The point of a Property is usually that you have a get and set function, that can be used mostly like a variable. Your first example is really wierd - why not just make the getter only public? Readonly and Writeonly properties are not a uncommon sight:
//Public property with private get or writeonly
public int Prop { private get; set; }
//Readonyl property
public int Prop { get; private set; }
One important rule regarding the Backing field: It is very important that you do not mix up the Property and it's backing field, especially in class code. If you use Autoimplement Properties, that danger is non-existant. If your code is more complex than that, a common approach is to append a underscore (_) to the backing field name. Prop/prop is too easy to mix up. _Prop and Prop are really hard to mix up ,especialyl for autocompletion features.
In general, methods represent actions and properties represent data. While both your examples can be used identically, the 'proper' way of representing state is through properties, and using properties correctly tells consumers of your object that this is representing state, not an action.
You should also consider how things like serialization and intellisense are expecting properties instead of methods.
I have a base class and a derived class. Each has the same property which has a private setter so the value can be set by some logic inside the class.
class First
{
internal virtual int Value { get; private set; }
void SetValue(int toValue)
{
Value = toValue;
}
}
class Second : First
{
internal override int Value { get; private set; }
void SetValue(int toValue)
{
Value = toValue;
}
}
This is resulting in a compiler error:
The property or indexer ... cannot be used in this context because the
set accessor is inaccessible.
Why is that the case, and how can I achieve what I'm trying to do? Is this not possible with auto-implemented properties, in other words, do I have to use a backing field instead?
Second would be unable to set the value of Value from First due to Values setter being private. If you need your subclass to be able to set it, it needs to be protected in the base.
Getters and Setters are basically methods. You can't override methods you can't see. The virtual in this case only applies to the getter as virtual private is not allowable.
It's not just that you can't see it to use it, you cannot override it at all.
I have this code:
public string foo { get; set; }
Now, I interpret this as my object has a public property called foo, and both it's accessor's are public. If I write this:
private string foo { get; set; }
I interpret that as my object has a private property called foo, and both it's accessor's are private. I understand making the property itself private. What I don't understand is why the accessor's must be more restrictive? If I write:
private string foo { public get; public set; }
I interpret that my object has a private property called foo, and both's it's accessor's are public, which is the behavior that I want. I'd like the private property with public accessors. I mean, if I have to write a Get/Set method, I will. But I'm just confused as to why this is.
A property is actually (under water) nothing more than two methods:
public string foo { get; set; }
will translate into:
public string get_foo() { ... }
public void set_foo(string value) { ... }
These methods can only have ONE access modifier, not a combination of two.
If I remember correcly, C#v1 did not support access modifiers for the getters and setters. There was one access modifers for the property which was used for both functions.
In v2 it was possible to "override" one of getter/setter-pair, this way overrwriting the "other" function. There was no use to override both getters/setters, because in that would render the property-access modifier useless.
Why the access modifier for the getter/setter is more restrictive has, in my opinion, something to do with easier implementing interfaces which always have (implicitly public) properties.
For more info, read: http://msdn.microsoft.com/en-us/library/75e8y5dd(v=vs.80).aspx
Why you need such a property
private string foo { public get; public set; }
If you want to have you get set public, then make the property public.
The compiler will first check the access of the property and then its method. If the property is public then its method can have either public or private or any accessor
Take for example following code from a class:
public class Employee : IEntity
{
public string FirstName { get; set; }
public string LastName { get; set; }
public int EmployeeID { get; set; }
}
public class Company : IEntity
{
public string Name { get; set; }
public string TaxID { get; set }
}
I always used get; and set; with something in braces. I never left them like this.
Writing just:
get; set;
What it means?
Auto-Implemented Properties
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, the
compiler creates a private, anonymous
backing field that can only be
accessed through the property's get
and set accessors.
These are called Auto-Implemented Properties:
http://msdn.microsoft.com/en-us/library/bb384054.aspx
The compiler will generate a backing field, similar to this code:
public class Company : IEntity
{
public string Name
{
get { return _Name; }
set { _Name = value; }
}
private string _Name;
}
It was decided that this syntax could be made much shorter, but still keep all the same utility, hence Auto-Implemented Properties were born :)
Just look at it as an quick and easy C# way of giving you a read write permission over a variable.
One of the good things of C# if you ask me.
The other answers pretty much tell you everything else there is to know about auto get set.
Even though these two quotes seem somewhat conflicting:
CD said:
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, the
compiler creates a private, anonymous
backing field that can only be
accessed through the property's get
and set accessors.
While Merlyn Morgan-Graham said:
These are called Auto-Implemented
Properties:
http://msdn.microsoft.com/en-us/library/bb384054.aspx
The compiler will generate a backing
field, similar to this code:
public class Company : IEntity {
public string Name
{
get { return _Name; }
set { _Name = value; }
}
private string _Name; }
It was decided that this syntax could
be made much shorter, but still keep
all the same utility, hence
Auto-Implemented Properties were born
:)
To me that seems like CD said it does create a condition whilst Merlyn Morgan-Graham said there are none.
I think CD is correct when stating you can longer use , for example, the setters write permission as a response to also change whatever it's writing.
private int x = 3;
public int _x { get; set /*Change x*/; }
You would have to use the normal get set construction for that
If both get and set are compulsory in C# automatic properties, why do I have to bother specifying "get; set;" at all?
Because you might want a read-only property:
public int Foo { get; private set; }
Or Write-only property:
public int Foo { private get; set; }
ERROR: A property or indexer may not be passed as an out or ref parameter
If you didn't specify {get; set;} then the compiler wouldn't know if it's a field or a property.
This is important becasue while they "look" identical the compiler treats them differently. e.g. Calling "InitAnInt" on the property raises an error.
class Test
{
public int n;
public int i { get; set; }
public void InitAnInt(out int p)
{
p = 100;
}
public Test()
{
InitAnInt(out n); // This is OK
InitAnInt(out i); // ERROR: A property or indexer may not be passed
// as an out or ref parameter
}
}
You shouldn't create public fields/Variables on classes, you never know when you'll want to change it to have get & set accessors, and then you don't know what code you're going to break, especially if you have clients that program against your API.
Also you can have different access modifiers for the get & set, e.g. {get; private set;} makes the get public and the the set private to the declaring class.
Just thought I would share my findings on this topic.
Coding a property like the following, is a .net 3.0 shortcut call “auto-implemented property”.
public int MyProperty { get; set; }
This saves you some typing. The long way to declare a property is like this:
private int myProperty;
public int MyProperty
{
get { return myProperty; }
set { myProperty = value; }
}
When you use the “auto-implemented property” the compiler generates the code to wire up the get and set to some “k_BackingField”. Below is the disassembled code using Reflector.
public int MyProperty
{
[CompilerGenerated]
get
{
return this.<MyProperty>k__BackingField;
}
[CompilerGenerated]
set
{
this.<MyProperty>k__BackingField = value;
}
}
disassembled C# code from IL
Also wires up a method for the setter and getter.
[CompilerGenerated]
public void set_MyProperty(int value)
{
this.<MyProperty>k__BackingField = value;
}
[CompilerGenerated]
public int get_MyProperty()
{
return this.<MyProperty>k__BackingField;
}
disassembled C# code from IL
When you declare a read only auto-implemented property, by setting the setter to private:
public int MyProperty { get; private set; }
All the compiler does flag the "set" as private. The setter and getter method say the same.
public int MyProperty
{
[CompilerGenerated]
get
{
return this.<MyProperty>k__BackingField;
}
private [CompilerGenerated]
set
{
this.<MyProperty>k__BackingField = value;
}
}
disassembled C# code from IL
So I am not sure why the framework require both the get; and set; on an auto-implemented property. They could have just not written the set and setter method if it was not supplied. But there may be some compiler level issue that makes this difficult, I don't know.
If you look at the long way of declaring a read only property:
public int myProperty = 0;
public int MyProperty
{
get { return myProperty; }
}
And then look at the disassembled code. The setter is not there at all.
public int Test2
{
get
{
return this._test;
}
}
public int get_Test2()
{
return this._test;
}
disassembled C# code from IL
Because you need some way to distinguish it from plain fields.
It's also useful to have different access modifiers, e.g.
public int MyProperty { get; private set; }
The compiler needs to know if you want it to generate a getter and/or a setter, or perhaps are declaring a field.
If the property didn't have accessors, how would the compiler separate it from a field? And what would separate it from a field?
Well, obviously you need a way of disambiguating between fields and properties. But are required keywords really necessary? For instance, it's clear that these two declarations are different:
public int Foo;
public int Bar { }
That could work. That is, it's a syntax that a compiler could conceivably make sense of.
But then you get to a situation where an empty block has semantic meaning. That seems precarious.
Since no one mentioned it... you could make the auto-property virtual and override it:
public virtual int Property { get; set; }
If there was no get/set, how would it be overridden? Note that you are allowed to override the getter and not the setter:
public override int Property { get { return int.MinValue; } }
Also, because ever since C# 6.0 (in Visual Studio 2015, at the time of this answer available in version Ultimate Preview) you may implement a true read-only property:
public string Name { get; }
public string Name { get; } = "This won't change even internally";
... as opposed to currently imperfect workaround with public getter/private setter pair:
public string Name { get; private set; }
public Constructor() { Name="As initialised"; }
public void Method() { Name="This might be changed internally. By mistake. Or not."; }
Example of the above below (compiled and executable online here).
using System;
public class Propertier {
public string ReadOnlyPlease { get; private set; }
public Propertier() { ReadOnlyPlease="As initialised"; }
public void Method() { ReadOnlyPlease="This might be changed internally"; }
public override string ToString() { return String.Format("[{0}]",ReadOnlyPlease); }
}
public class Program {
static void Main() {
Propertier p=new Propertier();
Console.WriteLine(p);
// p.ReadOnlyPlease="Changing externally!";
// Console.WriteLine(p);
// error CS0272: The property or indexer `Propertier.ReadOnlyPlease' cannot be used in this context because the set accessor is inaccessible
// That's good and intended.
// But...
p.Method();
Console.WriteLine(p);
}
}
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