Added: LDM Notes for Nov. 13, 2019

[agocke]

https://github.com/dotnet/csharplang/blob/master/meetings/2019/LDM-2019-11-13.md

Agenda:

1. Discriminated unions
2. Improved analysis of [MaybeNull]T

[alrz]

enum class Expr
{
    enum class BinaryOperator
    {
        Add(Expr left, Expr right),
        Multiply(Expr left, Expr right)
    }
}

Instead of this, I would prefer a way to define DUs as sibling classes for more complex type hierarchies, Roslyn AST is a good example here.

In general, for both records and DUs, I think there could be a compact and expanded syntax forms, the latter would provide more control over things. The IDE could help to switch between the two.

[erik-kallen]

Since you are considering improving nullable reference type handling, can you please have a look at #2830 and the problem it describes as well. I don't think nullable reference types are very useful in web apps until the problem described in that issue is fixed.

[MgSam]

Could someone post a full example using enum class? I'm not fully understanding the semantics from the proposal without a full example declaration and usage. Also, it seems to require records as a pre-requisite- is that the case?

[333fred]

The examples in the proposal are about as fleshed-out as we have, currently. We haven't yet talked about how you would construct these, for example. And yes, record types are a prerequisite for unions.