Nullable Spec Issue List

[gafter]

These are things that should be spelled out in the nullable reference types feature specification:

• The handling of a lifted operator (if a comparison operator, the return type is still bool, but other operators have value types turned into Nullable of that value type, and reference types are made nullable. If either operand might be null, then the result might be null if the resulting return type is capable containing null.

• In order to preserve the safety in the face of unconstrained type parameters, we warn immediately when a null value of such a type is introduced. This is a safety warning. The contexts in which such a warning are given are

• default and default(T)

• null conversion to T (when T is known to be ref type)

• e?.M() when the return type is T

• dynamic conversion or cast to T when the dynamic might be null

• explicit conversion to T

• e as T when there is not an implicit conversion from the type of e to T

• a call to a method like FirstOrDefault() that is annotated with `[MaybeNull] (not yet implemented)

[BillWagner]

Not moving this as the standards committee is not yet working on C# 8

[BillWagner]

I'll transfer this to the csharpstandard repo now. I think most of these have been handled in the update for C# 8, but the committee as a whole should check that work.

Note the point of default and default(T) may need to wait for spec work on C# 9.

[jskeet]

(Self-assigned for the sake of triage/investigation, not actually fixing the issue...)

[jskeet]

Proposal for how we move forward on this:

• Someone offers to evaluate how many of these are already covered in the draft as it stands
• If anything isn't already covered, we decide on a case-by-case basis whether it needs fixing for C# 8 or can wait for C# 9