How to Use the Null Coalescing Assignment Operator in C#

The null coalescing assignment operator (??=) introduced in C# 8.0 provides a cleaner way to assign a value to a variable only when it's null. Let's see how and when to use it effectively.

Quick Example

// Instead of writing this:
if (myVariable == null)
    myVariable = defaultValue;

// You can write this:
myVariable ??= defaultValue;

Real-World Examples

Simple Property Initialization

public class UserSettings
{
    private List<string> _preferences;
    
    public List<string> Preferences
    {
        get
        {
            _preferences ??= new List<string>();
            return _preferences;
        }
    }
}

Service Caching

public class ServiceCache
{
    private ApiClient _client;
    
    public ApiClient GetClient()
    {
        _client ??= new ApiClient("https://api.example.com");
        return _client;
    }
}

Lazy Configuration Loading

public class ConfigurationManager
{
    private Dictionary<string, string> _settings;
    
    public string GetSetting(string key)
    {
        _settings ??= LoadSettingsFromFile();
        return _settings.TryGetValue(key, out var value) ? value : null;
    }
    
    private Dictionary<string, string> LoadSettingsFromFile()
    {
        // Load settings logic here
        return new Dictionary<string, string>();
    }
}

Common Gotchas

Reference vs Value Types

The operator works differently with value types - they need to be nullable:

// This won't compile
int count ??= 1;

// This works
int? count ??= 1;

Chaining Operations

// You can chain the operator
string result = first ??= second ??= "default";

// Equivalent to:
if (first == null)
{
    if (second == null)
    {
        second = "default";
    }
    first = second;
}
result = first;

Thread Safety

The operator is not thread-safe by default:

// Not thread-safe
public class SharedCache
{
    private static Dictionary<string, object> _cache;
    
    public object GetItem(string key)
    {
        // Multiple threads could evaluate null simultaneously
        _cache ??= new Dictionary<string, object>();
        return _cache.GetValueOrDefault(key);
    }
}

// Thread-safe version
public class SharedCache
{
    private static Dictionary<string, object> _cache;
    private static readonly object _lock = new object();
    
    public object GetItem(string key)
    {
        lock (_lock)
        {
            _cache ??= new Dictionary<string, object>();
            return _cache.GetValueOrDefault(key);
        }
    }
}

Performance Considerations

The null coalescing assignment operator is compiled to efficient IL code. It generally performs the same as an explicit null check:

// These compile to similar IL
obj ??= new object();

if (obj == null)
    obj = new object();

When to Use It

✅ Good use cases:

  • Lazy initialization of properties
  • Caching values
  • Setting default values for nullable types
  • Simplifying null checks in property getters

❌ Avoid using when:

  • You need thread-safe initialization (use Lazy<T> instead)
  • The right-hand expression has side effects
  • You need more complex null-checking logic

Visual Studio Tips

You can use Quick Actions (Ctrl+.) to convert between traditional null checks and the ??= operator. Look for the suggestion "Use null coalescing assignment" when you have a pattern like:

if (variable == null)
    variable = value;

Version Compatibility

This feature requires:

  • C# 8.0 or later
  • .NET Core 3.0+ or .NET Standard 2.1+
  • Visual Studio 2019+
1
52

Related

Raw string literals in C# provide a flexible way to work with multiline strings, with some interesting rules around how quotes work.

The key insight is that you can use any number of double quotes (three or more) to delimit your string, as long as the opening and closing sequences have the same number of quotes.

The Basic Rules

  1. You must use at least three double quotes (""") to start and end a raw string literal
  2. The opening and closing quotes must have the same count
  3. The closing quotes must be on their own line for proper indentation
  4. If your string content contains a sequence of double quotes, you need to use more quotes in your delimiter than the longest sequence in your content

Examples with Different Quote Counts

// Three quotes - most common usage
string basic = """
    This is a basic
    multiline string
    """;

// Four quotes - when your content has three quotes
string withThreeQuotes = """"
    Here's some text with """quoted""" content
    """";

// Five quotes - when your content has four quotes
string withFourQuotes = """""
    Here's text with """"nested"""" quotes
    """"";

// Six quotes - for even more complex scenarios
string withFiveQuotes = """"""
    Look at these """""nested""""" quotes!
    """""";

The N+1 Rule

The general rule is that if your string content contains N consecutive double quotes, you need to wrap the entire string with at least N+1 quotes. This ensures the compiler can properly distinguish between your content and the string's delimiters.

// Example demonstrating the N+1 rule
string example1 = """
    No quotes inside
    """; // 3 quotes is fine

string example2 = """"
    Contains """three quotes"""
    """"; // Needs 4 quotes (3+1)

string example3 = """""
    Has """"four quotes""""
    """""; // Needs 5 quotes (4+1)

Practical Tips

  • Start with three quotes (""") as your default
  • Only increase the quote count when you actually need to embed quote sequences in your content
  • The closing quotes must be on their own line and should line up with the indentation you want
  • Any whitespace to the left of the closing quotes defines the baseline indentation
// Indentation example
string properlyIndented = """
    {
        "property": "value",
        "nested": {
            "deeper": "content"
        }
    }
    """; // This line's position determines the indentation

This flexibility with quote counts makes raw string literals extremely versatile, especially when dealing with content that itself contains quotes, like JSON, XML, or other structured text formats.

1
71

File-scoped namespaces, introduced in C# 10, provide a more concise way to declare namespaces in your code files.

This feature helps reduce nesting levels and makes your code cleaner and more readable. Let's explore how to use them effectively and understand their benefits.

Traditional Namespace Declaration

Traditionally, C# developers have used block-scoped namespaces, which require curly braces and add an extra level of indentation:

namespace MyCompany.MyProduct.Features
{
    public class UserService
    {
        private readonly string _connectionString;

        public UserService(string connectionString)
        {
            _connectionString = connectionString;
        }

        public void CreateUser(string username)
        {
            // Implementation
        }
    }

    public record User(string Username, string Email);
}

Modern File-Scoped Namespace

With file-scoped namespaces, you can declare the namespace without braces, reducing indentation and making the code more readable:

namespace MyCompany.MyProduct.Features;

public class UserService
{
    private readonly string _connectionString;

    public UserService(string connectionString)
    {
        _connectionString = connectionString;
    }

    public void CreateUser(string username)
    {
        // Implementation
    }
}

public record User(string Username, string Email);

Key Benefits and Best Practices

  1. Reduced Indentation: File-scoped namespaces eliminate one level of indentation, making the code easier to read and maintain.

  2. Single Namespace per File: File-scoped namespaces enforce a good practice of having only one namespace per file, improving code organization.

  3. Compatibility: File-scoped namespaces work seamlessly with existing code and can be gradually adopted in your codebase.

Important Considerations

When using file-scoped namespaces, keep these points in mind:

  • You can only have one namespace declaration per file
  • The namespace declaration must be the first non-comment line in the file
  • You cannot mix traditional and file-scoped namespace declarations in the same file

Migration Tips

When converting existing code to use file-scoped namespaces:

  1. Start with new files, using file-scoped namespaces from the beginning
  2. Gradually convert existing files during regular maintenance work
  3. Use IDE tools to automate the conversion process
  4. Ensure your team agrees on the migration approach and timeline

Conclusion

File-scoped namespaces are a simple yet effective feature that can make your C# code more readable and maintainable. While the benefits might seem small, they add up significantly in larger codebases. Consider adopting this modern syntax in your C# projects, especially if you're using C# 10 or later.

0
113

When working with URLs in C#, encoding is essential to ensure that special characters (like spaces, ?, &, and =) don’t break the URL structure. The recommended way to encode a string for a URL is by using Uri.EscapeDataString(), which converts unsafe characters into their percent-encoded equivalents.

string rawText = "hello world!";
string encodedText = Uri.EscapeDataString(rawText);

Console.WriteLine(encodedText); // Output: hello%20world%21

This method encodes spaces as %20, making it ideal for query parameters.

For ASP.NET applications, you can also use HttpUtility.UrlEncode() (from System.Web), which encodes spaces as +:

using System.Web;

string encodedText = HttpUtility.UrlEncode("hello world!");
Console.WriteLine(encodedText); // Output: hello+world%21

For .NET Core and later, Uri.EscapeDataString() is the preferred choice.

27
665