LDM notes for 2018-09-19

meetings/2018/LDM-2018-09-19.md

@@ -0,0 +1,108 @@
+
+# C# Language Design Notes for September 19, 2018
+
+## Agenda
+
+Triage:
+
+1. XML doc comment features
+2. New `foreach` pattern using `Length` and indexer
+3. Object initializers for `readonly` members
+4. `readonly` struct methods
+5. `params Span<T>`
+6. Nullable reference type features on `Nullable<T>`
+
+## Discussion
+
+### XML Doc and related features
+
+Proposals:
+
+- https://github.com/dotnet/csharplang/issues/313
+- https://github.com/dotnet/csharplang/issues/1766
+- https://github.com/dotnet/csharplang/issues/1767
+- https://github.com/dotnet/csharplang/issues/1768
+- https://github.com/dotnet/csharplang/issues/315
+- https://github.com/dotnet/csharplang/issues/320
+- https://github.com/dotnet/csharplang/issues/401
+- https://github.com/dotnet/csharplang/issues/1764
+- https://github.com/dotnet/csharplang/issues/1765
+
+We're not very excited about designing features in doc comments, primarily
+because a lot of design work depends more on tooling ecosystem than language
+design. It seems like there's a lot of coordination that should happen
+outside LDM before we look at it inside LDM. Most of the features aren't
+useful without a near-term guarantee of tooling support.
+
+**Conclusion**
+
+We need the tooling and ecosystem designers and owners to weigh in before
+we're ready to move forward. Specifically, we need a fully fleshed out,
+detailed proposal for exactly what the total work is and a timeline for
+completion. Once that's in place, we should consider all the XML doc comment
+changes at once. We're moving this into an `X.0` release, since we think the
+tooling changes merit a major release and we are blocked on external work.
+
+### New `foreach` pattern using `Length` and indexer
+
+Proposal: https://github.com/dotnet/csharplang/issues/1424
+
+There are a bunch of options around signaling support for this feature
+without incurring a breaking change, including using an attribute, using a
+new interface, considering a new pattern (including the ref/ref-readonly
+variants). `foreach` already has a lot of different variants, so any change
+has to fully account for all the possibilities.
+
+It's also notable that we've seen LINQ performance as a concern for quite a
+while and we haven't ruled out doing something for that. If we add a new
+interface for LINQ we might want to use the same interface as a trigger for
+new optimizations here. We almost certainly wouldn't want to create a
+duplicate interface.
+
+**Conclusion**
+
+We don't like this specific proposal, but will continue to look at features
+in this area.
+
+### Readonly object initializers
+
+Proposal: https://github.com/dotnet/csharplang/issues/1684
+
+**Conclusion** 
+
+A lot of crossover with records proposals here. This seems like more of a special
+case -- let's see if we can make a generalization work before we go this route.
+
+### `readonly` functions on structs
+
+Proposal: https://github.com/dotnet/csharplang/issues/1710
+
+First concern is ordering restrictions of the "readonly" modifier. It can
+also indicate a "readonly ref" return type, so we need to make sure it's not
+ambiguous.
+
+There's also another option: do we allow explicit receivers so the user could
+specify `void M(in this S s)` and explicitly declare the variables which are
+readonly?
+
+**Conclusion**
+
+We're interested. Let's keep the design as-is for now.
+
+### `params Span<T>`
+
+Proposal: https://github.com/dotnet/csharplang/issues/1757
+
+This would be especially interesting if the CLR implements a new feature for
+stack allocating an array of reference types.
+
+**Conclusion**
+
+Let's keep it in C# 8. A lot of stuff to work out here.
+
+### Add nullable reference type features to nullable value types
+
+Proposal: https://github.com/dotnet/csharplang/issues/1865
+
+Let's look at this for 8.0 if only to make sure doing it later is not
+a breaking change.

meetings/2018/README.md

@@ -116,12 +116,20 @@ We continued to discuss the range operator in C# and the underlying types for it
 1. Nullability of constraints in inheritance and interface implementation
 2. Static local functions
 
-# Upcoming meetings
-
 ## Sep 19, 2018
 
-- *Triage championed features*
-- *Triage milestones*
+[C# Language Design Notes for September 19, 2018](LDM-2018-09-19.md)
+
+Triage:
+
+1. XML doc comment features
+2. New `foreach` pattern using `Length` and indexer
+3. Object initializers for `readonly` members
+4. `readonly` struct methods
+5. `params Span<T>`
+6. Nullable reference type features on `Nullable<T>`
+
+# Upcoming meetings
 
 ## Sep 24, 2018