Fixed-Size buffer

Motivation

Fixed-size buffers are used to declare “C-style” in-line arrays as members of structs, and are primarily useful for interfacing with unmanaged APIs.

Constraint

• Length of fixed-size buffer may only be constant.
• Fixed-size buffer may only be declared and accessed in unsafe context.

C c = new();
_ = c.Buffer[0]; // CS0214
struct C
{
    public unsafe fixed byte Buffer[30];
    public unsafe void M()
    {
        C c = new();
        _ = c.Buffer[0]; // compiles
    }
}

• May not be static. But instance of its containing type can be static.

struct C
{
    public static unsafe fixed byte Buffer[30]; // [!code error]
    public unsafe void M()
    {
        C c = new();
        _ = c.Buffer[0]; // compiles
    }
}

• Element type must be one of the following: bool, byte, short, int, long, char, sbyte, ushort, uint, ulong, float or double.