Difference Between Property and Field in C# 3.0+

Difference between Property and Field in C# 3.0+

Encapsulation.

In the second instance you've just defined a variable, in the first, there is a getter / setter around the variable. So if you decide you want to validate the variable at a later date - it will be a lot easier.

Plus they show up differently in Intellisense :)

Edit: Update for OPs updated question - if you want to ignore the other suggestions here, the other reason is that it's simply not good OO design. And if you don't have a very good reason for doing it, always choose a property over a public variable / field.

What is the difference between a field and a property?

Properties expose fields. Fields should (almost always) be kept private to a class and accessed via get and set properties. Properties provide a level of abstraction allowing you to change the fields while not affecting the external way they are accessed by the things that use your class.

public class MyClass
{
    // this is a field.  It is private to your class and stores the actual data.
    private string _myField;

    // this is a property. When accessed it uses the underlying field,
    // but only exposes the contract, which will not be affected by the underlying field
    public string MyProperty
    {
        get
        {
            return _myField;
        }
        set
        {
            _myField = value;
        }
    }

    // This is an AutoProperty (C# 3.0 and higher) - which is a shorthand syntax
    // used to generate a private field for you
    public int AnotherProperty { get; set; } 
}

@Kent points out that Properties are not required to encapsulate fields, they could do a calculation on other fields, or serve other purposes.

@GSS points out that you can also do other logic, such as validation, when a property is accessed, another useful feature.

Difference between Automatic Properties and public field in C# 3.0

Because they are implemented differently in the resulting IL code (and machine language). An Automatic property is still exposed as a public getter and setter, whereas a public field is just that - a single field..

Thus, implementing an auto property allows you at some later date to change the internal behavior of either the getter or setter (like adding a validator) without recompiling or re=coding any dependant classes that use it...

C# field vs. property

I found out there is also a disadvantage to properties. They cannot be accessed by reference if they are of a value type. Why is this

Because under the covers, a property is just a method. If you look at the IL, you'll see methods like get_PropertyName and set_PropertyName. The problem with that is in order to support working with references, you would need to be able to return a reference for a method.

public ref T MyProperty
{
    get
    {
         return ref _underlyingField;
    }
}

Update: Starting in C# 7.0, this is possible using the syntax describe above.

Remainder of previous answer:

This of course, is something entirely possible in the CLR; but not exposed by the C# language.

Though it is possible, the CLR needs some tweaks to keep it as verifiable. The syntax for the property would have to support it to.

However, is any of that useful? As you stated, a field can do it. If you need it; use a field. Supporting it would take a lot of work. There are probably a very few cases where it is appropriate; and would create many cases where just using a field might have been better in the first place.

Why do we use fields & properties instead of just a variable?

Just for encapsulation principle. For hinding concrete implementaiton, and plus, you have an opportunity (in this case) to add additional code inside get/set.

If you don't need addittional code, you can use just

public string Name{get;set;}

or use fileds, as you would like. But using properties is a guideline offered by Microsoft.

So basically all, follow it.

C# 3.0 Autoproperties - whats the difference?

Fields and properties have many differences other than semantic.

1. Properties can be overridden to provide different implementations in descendants.
2. Properties can help alleviate versioning problems. I.e. Changing a field to a property in a library requires a recompile of anything depending on that library.
3. Properties can have different accessibility for the getter and setter.

What is the difference between a property and a variable

As many have pointed out, A is a field, B is a property.

The real question is, why should you care, and what to use?

I refer to a blog post of Jonathan Aneja:

(Its in VB, but it applies to C# as well ;))

So why use properties over fields, 5 reasons:

1. Fields can’t be used in Interfaces

You can’t enforce the existence of a
field in an object’s public contract
through an interface. For properties
though it works fine.

2. Validation

While your application currently may
not require any validation logic to
set a particular value, changing
business requirements may require
inserting this logic later. At that
point changing a field to a property
is a breaking change for consumers of
your API. (For example if someone was
inspecting your class via reflection).

3. Binary Serialization

Changing a field to a property is a
breaking change if you’re using binary
serialization. Incidentally, this is
one of the reasons VB10’s
auto-implemented properties have a
“bindable” backing field (i.e. you can
express the name of the backing field
in code) – that way, if you change an
auto-implemented property to an
expanded property, you can still
maintain serialization compatibility
by keeping the backing field name the
same (in C# you’re forced to change it
because it generates backing fields
with unbindable names).

4. A lot of the .NET databinding infrastructure binds to properties but not fields

I’ve heard arguments on both sides as
to whether or not that’s a good thing,
but the reality is that’s the way it
works right now. (Note from me: WPF bindings work on properties)

5. Exposing a public field is an FxCop violation

For many of the reasons listed above
:)

There might be more reasons.

I would also like to point to a blog post of Jeff Atwood and conclude with a quote from it:

The really important thing to take away here is to avoid writing code that doesn't matter. And property wrappers around public variables are the very essence of meaningless code.

C# autoproperty vs normal fields

AFAIK they behave exactly the same.

No they don't.

• Fields can't be used in data binding (at least in some binding implementations)
• You can add more logic later for properties without breaking source or binary compatibility
• Properties can't be passed by reference
• You can't add an initializer to an automatically implemented property
• They'll clearly be different in terms of reflection
• Philosophically, properties are logically part of the API whereas fields are an implementation detail

in c# you can always rewrite Foo into this: [...]

Well you can if you don't care about binary or source compatibility, yes. In some cases that's really not an issue - in other cases it's very, very much an issue. Why not make the choice to expose your API rather than your implementation details from the start? It's not like adding { get; set; } in your code is adding much clutter...

For more ranting, see my article on this.

c# using field with get and set methods vs using property

The functionality is almost identical. For "normal" code use-cases, these snippets will act exactly the same, as a property is in effect just a hidden field with two hidden methods (get and set).

However, there is a difference when it comes to reflection. Properties show up as PropertyInfo, and methods MethodInfo. You also can only bind to properties (in WPF/WinRT). Serialization also only works against properties. Both of these (and doubtlessly others) fail because they use reflection to find the members to act against.

So depending on your use case, they are the same. Generally speaking, I would stick with properties.

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