How to Set Property Default Values in C#: 5 Modern Techniques & Best Practices

In C#, setting default values for properties has evolved significantly across different versions of the language. Depending on your version of .NET, you can use several clean, readable approaches.

1. Auto-Implemented Property Initializers (C# 6.0+)

This is the most common and modern way to set a default value. It allows you to assign the value directly on the same line where the property is defined.

 

public class User Profile

{

// Sets the default value to "Guest"

public string Username { get; set; } = "Guest";

// Sets the default value for a numeric type

public int Age { get; set; } = 18;

// Works for read-only properties too

public DateTime CreatedAt { get; } = DateTime.UtcNow;

}

 

 

2. Using the Constructor

If your default value depends on logic, parameters, or you are using an older version of C#, the constructor is the standard place to initialize properties.

 

public class Order

{

public string Status { get; set; }

public Order()

{

Status = "Pending";

}

}

 

 

3. Required Properties (C# 11+)

Sometimes you don't want a "default" value, but rather to force the caller to provide one. The required keyword ensures the property is set during object initialization.

 

 

public class Car

{

public required string Vin { get; init; }

public string Make { get; set; } = "Generic";

}

// Usage:

// var myCar = new Car { Vin = "123XYZ" }; // Compiles

// var badCar = new Car(); // Compilation Error!

 

 

4. The DefaultValue Attribute (Metadata Only)

It is a common misconception that the [DefaultValue] attribute sets the value of a property. It does not. It is primarily used by visual designers (like WinForms or XAML) or documentation tools to communicate what the default should be.

 

using System.ComponentModel;

public class Settings

{

[DefaultValue(true)]

public bool IsEnabled { get; set; } = true; // You still must assign it!

}

 

 

5. Expression-Bodied Members (Read-Only)

If you want a property to always return a specific value (and never change), you can use the expression-bodied syntax.

 

public class Constants

{

public double Pi => 3.14159;

}

 

Which one should you use?

• Use Property Initializers for simple, static values (most common).

• Use Constructors if the initialization logic is complex or requires parameters.

• Use required if there is no sensible default and the user must provide data.