C# 12.0 introduces the InlineArrayAttribute which allows a struct to be annotated as an inline array. The array data is embedded directly in the struct, avoiding heap allocation and providing performance comparable to stack-allocated fixed-size buffers but with the safety of regular C# arrays.

Code

Now

[System.Runtime.CompilerServices.InlineArray(255)]
public struct Buffer
{
    private char _element0;
}

// Data is embedded in the struct, no heap allocation
var buffer = new Buffer();
for (int i = 0; i < 255; i++)
{
    buffer[i] = (char)i;
}

Before

// Heap-allocated array
var buffer = new char[255];
for (int i = 0; i < 255; i++)
{
    buffer[i] = (char)i;
}

More information

• What's new in C# 12.0
• Language reference