Allow "ReadOnlyValueReference<T>/ValueReference<T>" to accept ref structs via 'allow ref struct' as generic constraint

[CodingMadness]

Hey,

atleast for current .NEXT as new feature could you allow getting references to "ref structs" so you are not forced to update between ref structs via pointer.

Hope to hear from you and great work :)

[CodingMadness]

Same goes for all the "Intrincis" like "KeepAlive()" to use "allow ref struct" as generic constraint

[sakno]

There is no use case for KeepAlive with allow ref struct anti-constraint. ref struct lives on the stack, its lifetime is limited by the method stack frame.

[CodingMadness]

See for more info:

Proposal -> ref ->'ref Struct'
Discussion -> Discussion

[sakno]

I can't do that because .NEXT targets .NET 8, which is LTS version. I had experience with enabling language preview features, and it wasn't positive.

ValueReference will never use allow ref struct, because the reference cannot point to the stack location. Otherwise, you can use regular Span<T> or plain managed pointer.

[CodingMadness]

I cant use other managed pointers because i want inside a ref-struct, a reference to another ref struct and this is (up until now) not doable.

[sakno]

You can, but it's not safe (works in .NET 9):

public ref struct ByReference<T>
    where T : allows ref struct
{
    private ref byte reference;
			
    public ByReference(ref T reference)
    {
      this.reference = ref Unsafe.As<T, byte>(ref reference);
    }
			
    public ref T Reference => ref Unsafe.As<byte, T>(ref reference);
}

[CodingMadness]

You can, but it's not safe (works in .NET 9):

public ref struct ByReference<T>
    where T : allows ref struct
{
    private ref byte reference;
			
    public ByReference(ref T reference)
    {
      this.reference = ref Unsafe.As<T, byte>(ref reference);
    }
			
    public ref T Reference => ref Unsafe.As<byte, T>(ref reference);
}

why actually is it not safe, because I could use that to point to a variable/field which is out of stack frame?

[sakno]

See dotnet/csharplang#9152

[CodingMadness]

See dotnet/csharplang#9152

out of curiosity, since myself has participated in that discussion, is the main problem, for 'ref2refstruct' that it could point to local variables within a method and then obviously be dangling pointers once the stackframe gets cleared?

The fault-examples shown by the microsoft compiler dev signaled me that it is mostly that, mostly issues right now regarding pointing to local variables, or are there more main issues?