Delegate types are only synthesized for lambdas with parameter types and return type that are valid type arguments

[cston]

Delegates are currently only synthesized for lambda expressions and method groups when all parameter types and return type are valid as generic type arguments.

class Program
{
    unsafe static void Main()
    {
        var d1 = (ref int i) => { };  // ok
        var d2 = (int* p) => { };     // CS8917: The delegate type could not be inferred.
    }
}

[jaredpar]

I presume this includes ref struct as well hence Span<T> would be impacted