10 Essential C# 12 Features for High-Performance Applications

You should use new C# 12 Features to make fast apps. These features let you write code that works quickly and saves memory. You can fix problems fast and keep your projects easy to manage.

• Runs faster

• Uses resources better

• Easy code structure

Key Takeaways

• C# 12 brings new things like primary constructors and collection expressions. These help make your code shorter and easier to read. They also help your code run faster.

• New tools like inline arrays and ref readonly parameters give you more control over memory. They help your app work better by stopping extra data copying.

• Alias any type and default lambda parameters make hard code simpler. This makes it easier to write, understand, and fix your code.

• Interceptors and required members improvements keep your code neat and safe. They add extra checks and make sure you follow important rules.

• Better pattern matching and improved nameof scope help you write code that is clear and safe. This lowers bugs and makes it easier to change your code later.

1. Primary Constructors in C# 12 Features

Overview

Primary constructors let you put constructor parameters right in the class or struct line. You do not have to write a separate constructor method anymore. This makes your code shorter and easier to read. You can set up properties or fields where you declare them. You use the parameters from the primary constructor for this. This works for classes and structs, not just records.

You save time because you write less code. You make fewer mistakes since you do not repeat yourself. Your code is cleaner, so you can find errors faster.

Performance

Primary constructors help you make fast apps. You skip extra lines of code and keep your types small. You can set up members right away, so there is less work at runtime. This can make objects faster to create and use less memory. Your code is clear, so other people understand it quickly.

• Less extra code means fewer bugs.

• Setting things up right away makes things faster.

• Clean code is easier to fix and grow.

Example

Here is an easy example of primary constructors in C# 12 Features:

public class Author(int id, string firstName, string lastName)
{
    public int Id { get; } = id;
    public string FirstName { get; } = firstName;
    public string LastName { get; } = lastName;
}

Before C# 12, you had to write a separate constructor and set each property inside it. Now, you can do everything in one spot. This makes your code easier to read and fix. You can use this with structs too:

public readonly struct Rectangle(double x, double y)
{
    public readonly double Area { get; } = x * y;
}

With primary constructors, you write less code and your app runs better. Your code is also easier to read and change.

2. Collection Expressions

Overview

Collection expressions in C# 12 give you a new way to create and work with collections. You use square brackets to build arrays, lists, and spans. This new syntax makes your code shorter and easier to read. You do not need to write long initializers or repeat type names. You can see what goes into your collection at a glance.

With collection expressions, you write less code and make fewer mistakes. Your code looks clean and modern.

• You use square brackets to create collections.

• The syntax works for arrays, lists, and spans.

• You can embed collections inside other expressions.

• Your code becomes easier to maintain and understand.

Usage

You can use collection expressions in many places where you need to build collections quickly. This feature helps you when you want to:

• Create arrays, lists, or spans with a simple syntax.

• Merge collections using the spread operator (..).

• Handle memory buffers or fixed-length arrays in high-performance code.

• Reduce boilerplate and keep your code focused on logic.

The compiler helps you by generating efficient code. It sets the right capacity for your collections and avoids copying data you do not need. This saves memory and speeds up your app.

Example

Here are some ways you can use collection expressions in your code:

// Create an array
int[] numbers = [1, 2, 3, 4, 5];

// Create a list
List<int> scores = [10, 20, 30];

// Create a span
Span<DateTime> dates = [GetDate(0), GetDate(1)];

// Merge arrays with the spread operator
int[] first = [1, 2, 3];
int[] second = [4, 5, 6];
int[] combined = [.. first, .. second, 7, 8, 9];
// combined is [1, 2, 3, 4, 5, 6, 7, 8, 9]

You can see how collection expressions make your code shorter and more readable. You spend less time writing setup code and more time building features. This helps you write high-performance C# applications with less effort.

3. Inline Arrays

Overview

Inline arrays in C# 12 let you keep a fixed-size group of data inside a struct. You can put a buffer right in the struct. This means you do not use extra memory like normal arrays. Normal arrays are stored on the heap and are reference types. Inline arrays are value types with a set size and shape. This helps you control memory better. It also helps you write code that runs fast when every byte matters.

Inline arrays are great for things like games, graphics, or real-time systems. You always know how much memory you use. You can get to your data quickly.

You make an inline array by saying what type it holds and how long it is in your struct. You can use Span<T> or ReadOnlySpan<T> to work with the data safely. This keeps your code safe and fast.

Performance

Inline arrays give you real speed boosts. The array is inside the struct, so you do not use the heap. This means the garbage collector has less to do. Your code runs faster because the CPU finds the data more easily. Inline arrays also use less memory. This is good for apps that must be quick and use little memory.

• No heap use means less work for the garbage collector.

• Data is close together, so you get it faster.

• Using less memory helps you make fast, big apps.

You see these benefits in stack-based data or math problems. You need to get to small groups of values fast.

Example

Here is how you make and use an inline array in C# 12:

using System.Runtime.CompilerServices;

public struct PointBuffer
{
    private const int Length = 3;
    private InlineArray<int, Length> _points;
    
    public Span<int> Points => _points;
}

You can use the Points span like a normal array. But you do not use extra memory. Inline arrays help your code run faster and act the same every time. This is very helpful when you need to handle lots of small data sets quickly.

Tip: Inline arrays do not have every array feature. But they give you speed and control where you need it most.

4. Alias Any Type

Overview

Alias Any Type lets you give a short name to any type. You can use this for hard types like tuples or generic types. These short names work everywhere in your project. This helps you not write long type names again and again. Your code is easier to read with these short names. Using aliases makes your code look neat and clear. You can also change the type later by updating the alias in one place.

You get more control over your code. You can show what a type means with a simple name. This helps everyone on your team understand your code better.

Flexibility

Alias Any Type helps make your code easy to change and keep up. Sometimes you use tuples with many fields. Writing the whole tuple type each time is hard to read. Making an alias gives that tuple a simple, clear name. This makes your methods and variables easier to follow.

If you want to change your code later, aliases help. You can switch a tuple to a record type by changing the alias. You do not need to rewrite every spot in your code. You can use aliases in global using directives. This lets every file in your project use the same names. Your code stays neat and matches everywhere.

• You make LINQ code easier to read.

• You make APIs with hard types easier to use.

• You make constructor injection and patterns simpler.

• You write less extra code and focus on what matters.

Tip: Do not use too many aliases in classes with lots of inheritance or constructors. This can make things confusing for new team members.

Example

Here is how you use Alias Any Type in C# 12:

// Make a global alias for a tuple that is a 2D point
global using Point = (int X, int Y);

// Use the alias in your code
Point start = (0, 0);
Point end = (10, 20);

void DrawLine(Point from, Point to)
{
    Console.WriteLine($"Drawing from {from.X},{from.Y} to {to.X},{to.Y}");
}

You can also make aliases for harder types:

global using CoordinateStream = IAsyncEnumerable<(double Lat, double Lon)>;

With aliases, you write less code and show what you mean. Your team can see your data types quickly. If you want to add more features later, you can change the alias to a record type. You do not have to change every method. This keeps your code easy to change and take care of.

5. Default Lambda Parameters

Overview

Default lambda parameters in C# 12 let you set values for parameters if you do not give them. You can write lambdas that act like normal methods with default arguments. This feature gives you more ways to write your code. You do not need to make extra versions or write long lambdas. Your code gets shorter and easier to read.

With default lambda parameters, you do not make mistakes when you forget an argument. Your code looks cleaner and newer.

You can use this feature in many places. It works with delegates, LINQ queries, and event handlers. You can set a default value for any parameter in your lambda. This helps you write code that is strong and simple.

Usage

You use default lambda parameters when you want a backup value for a parameter. If you do not give a value, the lambda uses the default. This makes your code more flexible. You do not need to write many versions of the same lambda. You can handle optional logic in one spot.

Default lambda parameters help you avoid errors. If you forget an argument, the lambda still works. Your code is less messy. You can see what your code does right away. This makes it easier for you and your team to fix and change your code.

Benefits of default lambda parameters:

• You do not need many method versions

• Lambdas are shorter

• You make fewer mistakes from missing values

• Your code is easier to read

Example

Here is an easy example of default lambda parameters in C# 12:

Func<int, int, int> add = (x = 0, y = 0) => x + y;

int result1 = add();      // Returns 0 (x=0, y=0)
int result2 = add(5);     // Returns 5 (x=5, y=0)
int result3 = add(3, 4);  // Returns 7 (x=3, y=4)

You can also use default values in harder lambdas:

Func<int, int, int, int> calculate = (a, b, int multiplier = 1) => (a + b) * multiplier;

int total1 = calculate(2, 3);        // Returns 5 (multiplier=1)
int total2 = calculate(2, 3, 10);    // Returns 50 (multiplier=10)

Tip: Use default lambda parameters to keep your code simple. You will not make common mistakes. Your code will be easier to read and safer.

6. Ref Readonly Parameters

Overview

Ref readonly parameters in C# 12 let you pass large structs by reference without allowing changes. You use ref readonly in your method signature. This means you can read the data, but you cannot change it. The compiler checks your code and stops you from making mistakes. You get the speed of passing by reference and the safety of immutability.

You keep your data safe from accidental changes. Your code becomes easier to trust and maintain.

You often use ref readonly parameters in methods that work with large structs. This helps you avoid copying big chunks of data. You also make sure no one can change the data by accident.

Performance

You get two main benefits with ref readonly parameters:

• Speed: You avoid copying large structs. This saves memory and makes your app faster.

• Safety: You cannot change the data inside the method. The compiler gives you an error if you try.

When you use ref readonly, you combine performance with safety. You pass data by reference, so you do not waste time or memory. At the same time, you know the data stays the same. This is very helpful in high-performance or multi-threaded code. You avoid bugs that come from changing data by mistake.

Example

Here is how you use ref readonly parameters in C# 12:

public struct Point
{
    public int X;
    public int Y;
}

public void PrintPoint(ref readonly Point p)
{
    Console.WriteLine($"X: {p.X}, Y: {p.Y}");
    // p.X = 10; // ❌ This line would cause a compile-time error
}

If you try to change p.X or assign a new value to p, the compiler stops you. You can only read the fields. After the method runs, the original struct stays the same. This keeps your data safe and your code fast.

Tip: Use ref readonly when you want to protect data and boost performance at the same time. This feature helps you write reliable, high-speed C# code.

7. Interceptors

Overview

Interceptors are a new feature you can try in C# 12 Features. They let you change what happens when you use methods or properties. You can add things like logging or checking values without changing the main code. Interceptors let you put new actions before or after a method runs. This keeps your code neat and stops you from writing the same thing many times.

Interceptors help you handle things like security, speed checks, or fixing errors. You can do these jobs in one spot.

Interceptors are helpful if you want to change how your app works but do not want to edit every method. This is good for big projects. You keep your main code for business rules and put extra jobs somewhere else.

Usage

You use interceptors to watch or change method calls and property use. In EF Core, interceptors use special interfaces from IInterceptor. You set them up for each DbContext you use. Interceptors let you:

• Watch database commands, connections, and transactions

• Change or stop things before they happen

• Run code before and after each job

• Work with both normal and async code

This setup lets you control how your app talks to data. You can add your own actions around method calls. You do not have to change the real method. Your code stays easy to fix and update.

Note: Interceptors are still being tested. Try them out before using them for real work. Some things might change in later versions.

Example

Here is an easy example of using an interceptor in C# 12 Features. This interceptor writes a message every time a method runs:

public class LoggingInterceptor : IInterceptor
{
    public void BeforeExecute(string methodName)
    {
        Console.WriteLine($"Calling method: {methodName}");
    }

    public void AfterExecute(string methodName)
    {
        Console.WriteLine($"Finished method: {methodName}");
    }
}

// Register the interceptor
var dbContext = new MyDbContext();
dbContext.AddInterceptor(new LoggingInterceptor());

You can see the interceptor writes a message before and after each method call. You do not need to change the method itself. Your code stays neat and you can add new things easily.

Tip: Too many interceptors can make your app slow. Test your code to make sure it is still fast.

8. Required Members Enhancements

Overview

Required members enhancements in C# 12 help you control how objects are made. You can mark some properties or fields as required. This means anyone using your class must set these when making an object. C# 12 makes this easier with primary constructors and inheritance. Now, you can use required with new features for more safety and clear code.

Tip: Use required members so you do not forget to set important data. This helps you find mistakes early.

Usage

You use required members to make sure important data is always set. This is good for data models, APIs, and settings classes. C# 12 lets you:

• Mark properties or fields as required in classes, structs, and records.

• Use required with primary constructors for cleaner code.

• Keep required members in child classes, so your rules stay.

Benefits of required members enhancements:

• You stop bugs from missing values.

• Your code explains itself.

• You help others know what they must set.

Here is a quick checklist for using required members:

• Add the required keyword to important properties.

• Set values with object initializers or primary constructors.

• Check your code for missing required members. The compiler will warn you.

Example

Here is a simple example of required members in C# 12:

public class User(string username)
{
    public required string Username { get; } = username;
    public required string Email { get; set; }
}

// Correct usage
var user = new User("alice") { Email = "alice@example.com" };

// ❌ This will cause a compile-time error because Email is missing
// var user = new User("bob");

The compiler checks if you set all required members. This keeps your objects safe and your code strong. Use required members enhancements to make your C# 12 apps better and easier to take care of.

9. Improved Pattern Matching

Overview

Improved pattern matching in C# 12 gives you more power to write clear and fast code. You can now match data in new ways. This feature helps you handle complex checks with simple patterns. You do not need long chains of if-else statements. You use patterns to match types, values, and even lists. Your code becomes easier to read and maintain.

Pattern matching in C# 12 lets you write less code and avoid mistakes. You see the logic at a glance.

Usage

You use improved pattern matching to simplify complex conditional logic. C# 12 adds logical patterns like and, or, and not. You combine many checks into one pattern. You also use list patterns to match arrays or lists with different shapes. The compiler checks your patterns and warns you if you miss a case.

• You replace many if statements with a single switch expression.

• You use logical patterns to combine conditions.

• You match lists and arrays with slice operators.

• You capture values with var patterns and use when for extra checks.

• The compiler enforces that you cover all possible cases.

These features help you write code that is both safe and easy to change.

Example

Here is how you use improved pattern matching in C# 12:

object input = new int[] { 1, 2, 3 };

string result = input switch
{
    int[] [1, 2, ..] => "Starts with 1, 2",
    int[] [.., 3] => "Ends with 3",
    int n when n > 0 => "Positive number",
    string s when s.Length > 0 => $"String: {s}",
    null => "Null value",
    _ => "Unknown"
};

You see how one switch expression replaces many if-else checks. You match arrays with list patterns. You use when to add extra logic. This makes your code shorter, safer, and easier to understand. Improved pattern matching helps you write high-performance C# code with less effort.

10. Enhanced nameof Scope

Overview

The enhanced nameof scope in C# 12 lets you use nameof in more places. You can now use nameof for parameter names, properties, types, and generic type parameters. This means you do not have to write string names by hand. If you change a name, nameof updates it for you. This helps you make fewer mistakes and keeps your code safe.

Using nameof instead of writing strings makes your code neat. You also find mistakes sooner because the compiler checks your code.

Usage

You use the enhanced nameof scope to make your code safer and clearer. In big projects, you often need to use property or parameter names. Now, you can do this in more ways. This helps you when you:

• Check arguments and throw exceptions with the right names.

• Tell when a property changes in data-binding.

• Set action or controller names in MVC routing.

• Write logs and error messages that always match your code.

• Make database queries that stay correct when you change names.

You do not get bugs from old string names. Your team can change code without worry.

Example

Here is how you use the enhanced nameof scope in C# 12:

public void UpdateUser(string username)
{
    if (string.IsNullOrEmpty(username))
        throw new ArgumentNullException(nameof(username));
}

public class Product : INotifyPropertyChanged
{
    private string _name;
    public string Name
    {
        get => _name;
        set
        {
            _name = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Name)));
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
}

// Using nameof with generic type parameters
void LogTypeName<T>() => Console.WriteLine(nameof(T));

You can see that nameof keeps your code safe and easy to change. You do not have to look for string names when you rename things.

C# 12 Features Impact

C# 12 Features make nameof work in more places. This helps you write code that is safer and easier to take care of. In big projects, this means fewer mistakes when you change names. Your code stays neat and matches everywhere. Teams that use nameof with the new scope find fewer bugs and spend less time fixing names.

• You make refactoring safer.

• You keep logs and error messages correct.

• You help others understand your code.

Try the enhanced nameof scope to make your C# 12 projects safer and easier to manage.

You get a big benefit when you use C# 12 Features. These new tools help you write code that runs fast and stays safe. Your apps will be up-to-date.

• Big companies switch to .NET 8 and C# 12 for faster speed and better cloud help.

• The new features make things simple and help you work better. People in the community help pick what comes next.

Keep up by updating and learning about C# 12 Features. Try these tools now so you can make apps that are quick and ready for the future.

FAQ

What is the biggest benefit of using C# 12 features?

You can write code that works faster and uses less memory. Your code is also easier to read and fix. These features help you make modern apps that run well.

Can I use C# 12 features in older .NET projects?

You must have .NET 8 or newer to use C# 12 features. Update your project to the newest version. Then you can use all the new language tools.

Do primary constructors replace all other constructors?

No, you still need regular constructors for more setup steps. Primary constructors are good for simple types. Use them when you want easy and clear setup for classes or structs.

How do collection expressions improve performance?

Collection expressions help you make arrays and lists with less code. The compiler builds fast collections for you. This means fewer mistakes and a quicker app.

Are interceptors safe to use in production?

Interceptors are still being tested. Try them out in development first. Look for changes in new C# versions before using them in real apps.