C# 13

This release matters most when working close to allocations, spans, or generated code.

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Params collections

C# 13 expands params beyond array types.

public static void Log(params ReadOnlySpan<string> items)
{
    foreach (var item in items)
        Console.WriteLine(item);
}

Legacy style:

public static void Log(params string[] items)
{
    foreach (var item in items)
        Console.WriteLine(item);
}

In the right scenarios, the newer approach can avoid allocations and fit span-based APIs better.

New lock semantics

When the target of a lock statement is System.Threading.Lock, the compiler can generate code that uses the new lock type more directly.

private readonly System.Threading.Lock _gate = new();

lock (_gate)
{
    // protected section
}

This keeps the familiar lock syntax while enabling the newer semantics.

Method group natural type improvements

Method groups participate more naturally in type inference in additional scenarios.

var parser = int.Parse;

This reduces the need for explicit delegate type declarations in some assignments.

Partial properties and indexers

Partial properties and indexers can now be split across partial type declarations.

public partial class Sample
{
    public partial string Name { get; set; }
}

public partial class Sample
{
    private string _name = "";

    public partial string Name
    {
        get => _name;
        set => _name = value;
    }
}

This is mainly useful in source generation and similar advanced scenarios.

Ref struct interface support

C# 13 expands what ref struct types can do, including interface implementation in supported cases.

public ref struct TokenReader : IDisposable
{
    public void Dispose()
    {
    }
}

This improves the expressiveness of stack-only types and related low-level APIs.