Required members

Learn mandatory properties with the required keyword.

Required members

The required keyword forces a property to be set during object creation. Declaration: public required string Name { get; set; }.

If you skip it, new Person() is a compile error; you must write new Person { Name = "Alex" }. This catches missing-data errors at compile time. required can be combined with init to get a property that is both mandatory and immutable after creation.

required + init

Combining required and init gives a property that is both mandatory and immutable: public required string Name { get; init; }.

This combination creates record-like types. The value is set with an object initializer, cannot be changed afterwards, and the code does not compile without it. It is ideal for value objects in data-carrying classes. This is the standard form for data classes in modern C#.

Exercise Add a required property to the Person class

Define a Person class. Add a public required string Name { get; set; } property. Inside Main create an instance with new Person { Name = "Alex" } and print Name.

Show example solution

Add a required Name property to Person. In Main write Person p = new Person { Name = "Alex" }; Console.WriteLine(p.Name);
Example solution:
using System;

class Person
{
    public required string Name { get; set; }
}

class Program
{
    static void Main()
    {
        Person p = new Person { Name = "Alex" };
        Console.WriteLine(p.Name);
    }
}

Test yourself

Match each keyword to its behavior

required

Mandatory at init
init

Immutable after
set

Writable anytime
get

Reading
Which property is mandatory to set at initialization?
- public string Name { get; set; }
- public string Name { get; init; }
- public required string Name { get; set; }
- public string Name { get; }
Show answer

public required string Name { get; set; } — Correct. With required, the property must be set at initialization.

Complete the required property

public ____ string Name { get; set; }

Show answer

public required string Name { get; set; }

Next lesson: Summary - Encapsulation

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