C# 14.0 introduces a powerful set of enhancements that refine the developer experience, simplify code patterns, and enable new capabilities for high-performance and robust applications. In this guide, I explore the key features of C# 14.0 and how they build upon the foundations of C# 9–13 to help you write cleaner, more expressive, and safer code.
1. Parameters with params for Spans and Collections
In C# 14, the params keyword now supports ReadOnlySpan<T> and custom collection types, allowing developers to pass variable-length arguments with greater efficiency.
void Log(params ReadOnlySpan<string> messages)
{
foreach (var message in messages)
Console.WriteLine(message);
}
This change eliminates unnecessary allocations and enables low-overhead, high-performance APIs.
2. Enhanced Interpolated Strings
Interpolated string handlers continue to evolve. C# 14 improves their flexibility and introduces new performance-oriented APIs. These allow better formatting, logging, and serialization scenarios with reduced allocations.
[InterpolatedStringHandler]
public ref struct MyLogHandler { /* custom logic */ }
Log($"User ID: {user.Id}, Name: {user.Name}");
Interpolated string handlers now work in more contexts and can be used with ref struct and Span<char> efficiently.
3. Experimental Attributes and API Contracts
C# 14 introduces attributes like [Experimental] and [ObsoletedInVersion] to clearly signal API maturity and lifecycle. These metadata markers improve code maintenance, tooling support, and upgrade paths.
[Experimental("This API may change or be removed in future releases")]
public void TryNewFeature() { }
This helps development teams manage feature rollout and backward compatibility more transparently.
4. Required Members in Object Initialization
Now formalized and enforced, required properties ensure that specific values must be assigned during initialization, making models more robust.
public class UserProfile
{
public required string FirstName { get; init; }
public required string LastName { get; init; }
}
The compiler enforces required members, ensuring no accidental omission during object creation.
5. Collection Expressions
Inspired by array initializers, collection expressions allow developers to create and combine collections with cleaner syntax.
var numbers = [1, 2, 3];
var combined = [..numbers, 4, 5]; // Spread operator
This syntax works with arrays, lists, spans, and user-defined collection builders.
6. Pattern Matching Enhancements
C# 14 includes powerful pattern-matching additions, such as:
- List patterns
- Recursive patterns
- Relational & logical patterns
if (input is [1, 2, .. var rest])
{
Console.WriteLine($"Matched with rest: {string.Join(',', rest)}");
}
These constructs provide clearer, more expressive alternatives to complex conditional logic.
7. Primary Constructors in Classes
Previously limited to records, primary constructors are now available in classes, reducing boilerplate in immutable models and DTOs.
class Product(string name, decimal price)
{
public string Name { get; } = name;
public decimal Price { get; } = price;
}
This makes your models cleaner, especially in minimal APIs and domain logic layers.
8. Ref readonly Parameters and Returns in Async Methods
C# 14 lifts restrictions on using ref, readonly, and even unsafe operations inside async methods and iterators.
public async Task ProcessAsync()
{
ref readonly var data = ref GetData();
await Task.Delay(100);
}
This change enhances the power and flexibility of high-performance async workflows.
9. New Lock Object Type
A new Lock type has been introduced to replace using plain objects for synchronization, improving clarity and intent.
private readonly Lock _sync = new();
lock (_sync)
{
// Thread-safe section
}
It avoids common pitfalls associated with locking on public objects.
10. Escape Sequence \\e for ESC Character
A quality-of-life addition, C# 14 adds \\e as a native escape sequence for the ASCII escape character (\u001B), useful in terminal and CLI apps.
Console.WriteLine("\\e[1mBold Text\\e[0m");
11. Overload Resolution Priority
With OverloadResolutionPriorityAttribute, developers can guide the compiler toward choosing preferred overloads in ambiguous contexts.
[OverloadResolutionPriority(1)]
public void Print(int x) { }
[OverloadResolutionPriority(2)]
public void Print(object x) { }
This helps API authors manage method overloads more predictably.
12. Ref Structs Can Implement Interfaces
C# 14 enables ref struct types (stack-only structs) to implement interfaces, opening up new design patterns in low-level code.
public interface IWriter { void Write(); }
public ref struct BufferWriter : IWriter
{
public void Write() => Console.WriteLine("Writing from stack!");
}
Summary
C# 14.0 builds on the momentum of recent releases, delivering features that enhance expressiveness, performance, and safety. Whether you’re writing high-throughput APIs, UI code, or domain models, C# 14 equips you with powerful new tools for building the next generation of .NET applications.
Key Takeaways
- Write safer and cleaner code with required members and primary constructors.
- Use collection expressions and pattern matching for expressive logic.
- Benefit from low-level performance with span-based params, ref-returning async methods, and lock enhancements.
- Simplify overloads, async, and logging with new language constructs and metadata.