C# Required Keyword: What It Is and How to Use It

The required keyword in C# marks properties or fields that must be set during object initialization. It ensures that these members are assigned a value before the object is fully created, helping prevent errors from missing data.

How It Works

Think of the required keyword as a checklist for building an object. When you create an object from a class, some properties might be essential for it to work correctly. By marking these properties as required, C# forces you to provide values for them when you first make the object.

This is like assembling furniture with instructions that say "You must attach these parts first." If you skip them, the compiler will remind you to fix it before running the program. This helps catch mistakes early, making your code safer and easier to maintain.

Example

This example shows a class with required properties. You must set these properties when creating a new object, or the code will not compile.

csharp

public class Person
{
    public required string FirstName { get; init; }
    public required string LastName { get; init; }
    public int Age { get; init; }
}

class Program
{
    static void Main()
    {
        // Correct: required properties are set
        Person person = new Person { FirstName = "Alice", LastName = "Smith", Age = 30 };
        System.Console.WriteLine($"Name: {person.FirstName} {person.LastName}, Age: {person.Age}");

        // Incorrect: missing required property LastName (uncommenting causes compile error)
        // Person invalidPerson = new Person { FirstName = "Bob" };
    }
}

Output

Name: Alice Smith, Age: 30

When to Use

Use the required keyword when you want to make sure certain properties are always set when creating an object. This is especially useful for data models, configuration settings, or any class where missing values could cause bugs.

For example, if you have a Person class, it makes sense to require a first and last name because a person without a name is incomplete. This keyword helps enforce these rules at compile time, so you catch mistakes early instead of at runtime.

Key Points

• Required properties must be set during object initialization.
• They help prevent missing or incomplete data in objects.
• Works with init accessors to allow setting only at creation.
• Introduced in C# 11, so use with .NET 7 or later.

Key Takeaways

The required keyword enforces mandatory property assignment during object creation.

It helps catch missing data errors at compile time, improving code safety.

Use required with init-only properties to allow setting values only once.

This feature is available starting with C# 11 and .NET 7.

Required properties make your classes more robust and easier to use correctly.