C# Property Examples

Make properties with the get and set keywords. Understand that properties are used for data access.

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Property. An adventurer explores the ancient ruins. In a stone room a jar is found: it has a shape, a material, a volume. These are its properties. It is a beautiful jar.

Property use. With properties, we could model this jar. It is made from clay—its Material property returns "clay." Its size could be an integer.

First example. We introduce an Example class. One field, an integer, is present. It is used as a backing store for the Number property.
Number: This is an int property. Number provides get { } and set { } implementations.
Get: The get { } implementation must include a return statement. It can access any member on the class.
Set: The set { } implementation receives the implicit argument "value." This is the value to which the property is assigned.
C# program that uses public int property using System; class Example { int _number; public int Number { get { return this._number; } set { this._number = value; } } } class Program { static void Main() { Example example = new Example(); example.Number = 5; // set { } Console.WriteLine(example.Number); // get { } } } Output 5

Enum. This example shows the DayOfWeek enum type in a property. We also insert code in the getter (or setter) that checks the backing store or the parameter value.EnumDayOfWeek
Types: Like a method, a property can act on any type, even enum types like DayOfWeek. Many properties will use string or int.
C# program that uses enum property using System; class Example { DayOfWeek _day; public DayOfWeek Day { get { // We don't allow this to be used on Friday. if (this._day == DayOfWeek.Friday) { throw new Exception("Invalid access"); } return this._day; } set { this._day = value; } } } class Program { static void Main() { Example example = new Example(); example.Day = DayOfWeek.Monday; Console.WriteLine(example.Day == DayOfWeek.Monday); } } Output True

Private. We make a private property. Here the IsFound property can only be set in the Example class. We set it in the Example constructor.
Then: We can only get the property in the Program.Main method by using an Example instance.
C# program that uses private setter in property using System; class Example { public Example() { // Set the private property. this.IsFound = true; } bool _found; public bool IsFound { get { return this._found; } private set { // Can only be called in this class. this._found = value; } } } class Program { static void Main() { Example example = new Example(); Console.WriteLine(example.IsFound); } } Output True

Entire property. We can also make an entire property private. If we do this, we can only use the property in the same enclosing class.
Private: The Display method in the example shows how to use the private property.
Note: This syntax is less useful in most programs. But it exists, and may be helpful in a complex class.
C# program that uses private property using System; class Example { int _id; private int Id { get { return this._id; } set { this._id = value; } } public void Display() { // Access the private property in this method. this.Id = 7; Console.WriteLine(this.Id); } } class Program { static void Main() { Example example = new Example(); example.Display(); } } Output 7

Static. Properties can also be static. This means they are associated with the type and not an instance. Static classes can only have static properties.Static
Count: This property has a side effect. It causes the field to be incremented upon each access.
Caution: Side effects are not usually a good design feature in programs. They can make the logic hard to follow.
Setter: This is omitted. This makes sense for a property that computes a value entirely in memory, or based on other fields or properties.
C# program that uses static property using System; class Example { static int _count; public static int Count { get { // Side effect of this property. _count++; return _count; } } } class Program { static void Main() { Console.WriteLine(Example.Count); Console.WriteLine(Example.Count); Console.WriteLine(Example.Count); } } Output 1 2 3

Automatic. Next, we see automatically implemented property syntax. A hidden field is generated. Then, the get and set statements are expanded to use that hidden field.
Expression: The *= operator is used to multiply the property by itself. This is the same as "example.Number = example.Number * 4".
Tip: Because properties are meant to look like fields, this is allowed. Obviously methods are not allowed to do this.
C# program that uses automatically implemented property using System; class Example { public int Number { get; set; } } class Program { static void Main() { Example example = new Example(); example.Number = 8; example.Number *= 4; Console.WriteLine(example.Number); } } Output 32

Automatic, private. Let us consider how to make getters or setters on an automatic property. We cannot omit either the getter or setter in this kind of property.
Note: The error reported by the C# compiler reads: "Automatically implemented properties must define both get and set accessors."
C# program that uses private setter, auto property using System; class Example { public Example() { // Use private setter in the constructor. this.Id = new Random().Next(); } public int Id { get; private set; } } class Program { static void Main() { Example example = new Example(); Console.WriteLine(example.Id); } } Output 2077325073

Automatic, default values. Automatic properties have support for default values much like fields. Here we assign the Quantity property of Medication to 30 by default.
C# program that uses default value using System; class Medication { public int Quantity { get; set; } = 30; // Has default value. } class Program { static void Main() { Medication med = new Medication(); // The quantity is by default 30. Console.WriteLine(med.Quantity); // We can change the quantity. med.Quantity *= 2; Console.WriteLine(med.Quantity); } } Output 30 60

Expression-bodied properties. We can use lambda-style syntax to specify properties. These are expression-bodied properties—we use "get" and "set" and then the result on the right side.
C# program that uses expression-bodied properties class Program { private static int test; public static int Test { get => test; set => test = value; } static void Main() { // Use the property. Program.Test = 200; System.Console.WriteLine(Program.Test); } } Output 200

Benchmark, properties. Compiler optimizations ensure that properties are efficient. These same optimizations are used on methods, which share the underlying implementation with properties.
Version 1: This code uses a property. It sets a property, and then gets the value of the property.
Version 2: This version of the code uses a field directly. It performs the same logical steps that version 1 does.
Result: There was no difference in performance with the property and the field. It is apparent the property access is inlined.
Tip: The JIT compiler can inline properties that don't have logic inside of them. So they are as efficient as fields.
C# program that benchmarks properties using System; using System.Diagnostics; class Program { static string _backing; // Backing store for property. static string Property // Getter and setter. { get { return _backing; } set { _backing = value; } } static string Field; // Static field. static void Main() { const int m = 100000000; for (int x = 0; x < 10; x++) // Ten tests. { Stopwatch s1 = new Stopwatch(); s1.Start(); // Version 1: test property. for (int i = 0; i < m; i++) { Property = "string"; if (Property == "cat") { } } s1.Stop(); Stopwatch s2 = new Stopwatch(); s2.Start(); // Version 2: test field. for (int i = 0; i < m; i++) { Field = "string"; if (Field == "cat") { } } s2.Stop(); Console.WriteLine("{0},{1}", s1.ElapsedMilliseconds, s2.ElapsedMilliseconds); } Console.Read(); } } Output Property get/set: 604.6 ms Field read/assign: 603.6 ms

Indexers. These are properties. They allow element access (like an array). They use the token "this" for their name, and square brackets with an argument.Indexer

Interface. A property can be part of an interface. There is a special syntax for this. On types that implement the interface, we must provide implementations for the property.Interface

Prop. I like the prop snippet. It is one of my favorites. In Visual Studio, try typing prop and pressing tab twice where you want to put a property.
Then: Change the fields as needed. We get an automatically implemented property.

A review. Properties are used throughout programs. They are a powerful way to replace methods. They present a more intuitive way to use objects.

On a conceptual level, properties combine fields and methods. But in terms of implementation, properties are just methods. They are optimized, in the JIT compiler, just like methods.


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