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The this keyword

The this keyword refers to the current instance of the class. It also serves as a modifier for the first parameter of an extension method.

Note

This article discusses the use of this to refer to the receiver instance in the current member. For more information about its use in extension methods, see the extension keyword.

The C# language reference documents the most recently released version of the C# language. It also contains initial documentation for features in public previews for the upcoming language release.

The documentation identifies any feature first introduced in the last three versions of the language or in current public previews.

Tip

To find when a feature was first introduced in C#, consult the article on the C# language version history.

Common uses of this include:

  • Qualifying members hidden by similar names, such as:

    public class Employee
{
    private string alias;
    private string name;

    public Employee(string name, string alias)
    {
        // Use this to qualify the members of the class
        // instead of the constructor parameters.
        this.name = name;
        this.alias = alias;
    }
}

  • Passing an object as a parameter to other methods.

    CalcTax(this);

  • Declaring indexers, such as:

    public int this[int param]
{
    get => array[param];
    set => array[param] = value;
}

Static member functions exist at the class level and not as part of an object. They don't have a this pointer. Referring to this in a static method is an error.

In the following example, the parameters name and alias hide fields with the same names. The this keyword qualifies those variables as Employee class members. The this keyword also specifies the object for the method CalcTax, which belongs to another class.

class Employee
{
    private string name;
    private string alias;

    // Constructor:
    public Employee(string name, string alias)
    {
        // Use this to qualify the fields, name and alias:
        this.name = name;
        this.alias = alias;
    }

    // Printing method:
    public void printEmployee()
    {
        Console.WriteLine($"""
        Name: {name}
        Alias: {alias}
        """);
        // Passing the object to the CalcTax method by using this:
        Console.WriteLine($"Taxes: {Tax.CalcTax(this):C}");
    }

    public decimal Salary { get; } = 3000.00m;
}

class Tax
{
    public static decimal CalcTax(Employee E)=> 0.08m * E.Salary;
}

class Program
{
    static void Main()
    {
        // Create objects:
        Employee E1 = new Employee("Mingda Pan", "mpan");

        // Display results:
        E1.printEmployee();
    }
}
/*
Output:
    Name: Mingda Pan
    Alias: mpan
    Taxes: $240.00
 */

C# language specification

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

See also

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