C# 13 `params ReadOnlySpan<T>` Zero-Allocation Parameter Arrays

1Concept

Prior to C# 13, `params T[]` allocated a new heap array on every method invocation. C# 13 introduces `params ReadOnlySpan<T>`, allocating the arguments directly on the caller's stack with zero GC heap allocations.

2Architecture Diagram

Legacy params int[] (C# 12 and older):
Invocation ──> Allocates `new int[3]` on Managed Heap ──> GC Garbage Created

Modern params ReadOnlySpan<int> (C# 13):
Invocation ──> Emits stackalloc buffer on Thread Stack ──> ZERO Heap Allocation!

3Code Example

using System;

public class ParamsSpanDemo
{
    // C# 13 params ReadOnlySpan<T>
    public static int SumAll(params ReadOnlySpan<int> numbers)
    {
        int sum = 0;
        foreach (int n in numbers)
        {
            sum += n;
        }
        return sum;
    }

    public static void Main()
    {
        // Stack allocated arguments!
        int total = SumAll(10, 20, 30, 40, 50);
        Console.WriteLine($"Zero-Heap-Allocation Sum: {total}");
    }
}

4Expected Output

Zero-Heap-Allocation Sum: 150

5Key Takeaways

• ✓`params ReadOnlySpan<T>` completely eliminates GC pressure from variable-argument methods.
• ✓RyuJIT vectorizes Span loops using SIMD (AVX2/AVX-512) automatically.
• ✓Can accept both inline arguments `SumAll(1, 2)` and existing arrays `SumAll(arr)` seamlessly.