InlineArray fails at runtime when declared as a ref struct.

[burkenyo]

It appears [InlineArray] structs cannot be ref structs because they need to be passed as generic arguments to helper methods in the runtime. I think this should be a compile-time error.

Version Used:
.NET 8 SDK 8.0.100
Compiler version: '4.9.0-2.23571.2 (d1b2e28)'. Language version: 12.0.

Steps to Reproduce:
run this:

using System;
using System.Runtime.CompilerServices;

TenChars x = new();

Console.WriteLine(((Span<Char>) x).Length);

RefTenChars y = new();

Console.WriteLine(((Span<Char>) y).Length);

[InlineArray(10)]
struct TenChars
{
    char _;
}

[InlineArray(10)]
ref struct RefTenChars
{
    char _;
}

The program fails when trying to convert variable y to Span<char>.

Expected Behavior:

An error is emitted at compile-time.

Actual Behavior:

An exception is thrown at runtime.

[AlekseyTs]

Runtime probably doesn't have this limitation, therefore, declaring the type is probably fine. But the type cannot be indexed or converted in C#, and the fact should be reported when an attempt is made to do that.

[burkenyo]

Runtime probably doesn't have this limitation, therefore, declaring the type is probably fine. But the type cannot be indexed or converted in C#, and the fact should be reported when an attempt is made to do that.

I would offer that one of the selling points of Inline Arrays is the ability to treat them as “span-ables”, so declaring something that can’t do that seems less useful.

Nevertheless, the new analyzer being introduced would definitely addresses this for me by letting me know at compile-time that it might not work as expected at run-time.

[burkenyo]

Thank you!