Add notes for July 17th, 2020
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meetings/2020/LDM-2020-07-13.md
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meetings/2020/LDM-2020-07-13.md
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# C# Language Design Meeting for July 6th, 2020
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## Agenda
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1. [Generics and generic type parameters in aliases](#Generics-and-generic-type-parameters-in-aliases)
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2. ["closed" enum types](#"closed"-enum-types)
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3. [Allow `ref` assignment for switch expressions](#Allow-`ref`-assignment-for-switch-expressions)
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4. [Null suppressions nested under propagation operators](#Null-suppressions-nested-under-propagation-operators)
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5. [Relax rules for trailing whitespaces in format specifier](#Relax-rules-for-trailing-whitespaces-in-format-specifier)
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6. [Private field consideration in structs during definite assignment analysis](#Private-field-consideration-in-structs-during-definite-assignment-analysis)
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7. [List patterns](#list-patterns)
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8. [Property-scoped fields and the `field` keyword](#Property-scoped-fields-and-the-field-keyword)
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9. [File-scoped namespaces](#file-scoped-namespaces)
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10. [Allowing `ref`/`out` on lambda parameters without explicit type](#Allowing-ref/out-on-lambda-parameters-without-explicit-type)
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11. [Using declarations with a discard](#Using-declarations-with-a-discard)
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12. [Top level statements and functions](#Top-level-statements-and-functions)
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13. [Implicit usings](#implicit-usings)
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## Quote of the day
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"It does actually seem like this pattern is the 98% case..."
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"I just want to disagree with something [redacted] said... [they] said [they] thought it was the 98% case that this would apply to, and I think it's 99..."
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"Not fair, I was going to say that."
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## Discussion
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This meeting was issue triage. There will not be much detail on any particular issue, just a general summary
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of the LDM's feeling and the milestone that we triaged to.
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### Generics and generic type parameters in aliases
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https://github.com/dotnet/csharplang/issues/1239
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In general, we want to make improvements in this area. We should also be open to making other enhancements
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in this space, such as allowing tuple syntax on the right side, or allowing C# keywords like `int`. There's
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also a set of features that we should investigate in parallel, such as globally-visible aliases or publicly-
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exported aliases.
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#### Conclusion
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Triaged for C# 10 for now so that we can look at the space hollistically in the near term.
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### "closed" enum types
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https://github.com/dotnet/csharplang/issues/3179
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This is a solution to the very common complaints around enum usage, particularly in switch expressions and other
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exhaustiveness scenarios. It will also work well with DUs, and we should make sure that whatever syntax we use
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there works well with closed or sealed enum types as well.
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#### Conclusion
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Triaged for C# 10 to look at in coordination with DUs.
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### Allow `ref` assignment for switch expressions
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https://github.com/dotnet/csharplang/issues/3326
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We like this proposal. You can already do this with ternaries, and it's odd that you can't do this with switch
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expressions as well. It's not high priority, but we'd be happy to see it in the language. Like ternaries, the
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ref version would not be target-typed.
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#### Conclusion
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Triaged for Any Time.
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### Null suppressions nested under propagation operators
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https://github.com/dotnet/csharplang/issues/3393
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This will be a breaking change, so we need to get it in as soon as possible.
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#### Conclusion
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C# 9 timeframe. We need to make a syntax proposal and approve it.
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### Relax rules for trailing whitespaces in format specifier
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https://github.com/dotnet/csharplang/issues/3414
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In reading this proposal, we're unsure whether the request was for _ignoring_ trailing spaces in format specifiers,
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or allowing them and including them in the format specifier. We think that either way this is interpreted, it will
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be confusing: trailing spaces are allowed in front of an interpolated expression and mean nothing, but for things
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like `DateTime`, spaces are valid parts of a format specifier and will be respected in the output. We think that
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either behavior here would be confusing, with no clear indication on which the user wants.
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#### Conclusion
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Rejected.
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### Private field consideration in structs during definite assignment analysis
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https://github.com/dotnet/csharplang/issues/3431
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This is a bug from the native compiler that had to be reimplemented in Roslyn for compat, but it's always been
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one of the prime candidates for a warning wave (and is already supported as an error in the compiler via the strict
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feature flag). There is some contention whether it should be a warning or an error in this wave. There is also a
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concern that this will combine with the `SkipLocalsInit` feature in C# 9 to expose an uninitialized memory hole in
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C# with no use of `unsafe` or `System.Unsafe` required.
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#### Conclusion
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We need to look at this ASAP to make sure that we don't unintentionally expose unsafety in the language without
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user intention. We'll schedule this for next week.
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### Remove restriction that optional parameters must be trailing
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https://github.com/dotnet/csharplang/issues/3434
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It's possible to define such methods in metadata with the correct attribute usage _and_ call them from C# today.
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This would just be about removing the restriction from _defining_ them in C#.
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#### Conclusion
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Triaged for Any Time.
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### List patterns
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https://github.com/dotnet/csharplang/issues/3435
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We have an open proposal that with a prototype. We like the general direction it takes, but we need to have more
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detailed design review of it and possibly make a few different decisions. This is a direction we want to take
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pattern matching in future releases, so we'll continue iterating on this.
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#### Conclusion
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Triaged into C# 10 for design work.
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### Property-scoped fields and the `field` keyword
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* https://github.com/dotnet/csharplang/issues/133
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* https://github.com/dotnet/csharplang/issues/140
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We've started doing design work around both of these issues. We should continue doing that.
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#### Conclusion
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Triaged into C# 10.
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### File-scoped namespaces
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https://github.com/dotnet/csharplang/issues/137
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This has been a large request for a long time that reflects the default of almost every single C# file written.
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There's still some design work to do, particularly in how that will affect `using` statements, but it's work
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that we should take on.
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#### Conclusion
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Triaged into C# 10.
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### Allowing `ref`/`out` on lambda parameters without explicit type
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https://github.com/dotnet/csharplang/issues/338
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We've heard this request a few times, and while we don't see any particular issue with this, it's not a priority
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for the team at this point. If a spec/implementation was provided we'd likely accept it but won't go out of our
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way to add it unless something else changes here.
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#### Conclusion
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Triaged to Any Time.
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### Using declarations with a discard
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https://github.com/dotnet/csharplang/issues/2235
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There's still some open design questions here, particularly around possibly ambiguous syntaxes. We need to keep
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iterating on this to find a design that we like.
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#### Conclusion
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Triaged for X.X, pending a new proposal.
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### Top level statements and functions
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https://github.com/dotnet/csharplang/issues/3117
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This is part 2 of the work we started in C# 9 with top-level statements: designing free-floating functions that
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can sit on the top level without any containing type. We need to continue examining this context of scripting
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unification, which we plan to continue doing on an ongoing basis.
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#### Conclusion
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Triage into C# 10 for ongoing discussion.
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### Implicit usings
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https://github.com/dotnet/csharplang/issues/3428
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This is another issue arising of discussions on top-level statements and using C# as a scripting language:
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attempting to make the language more brief by specifying common imports on the command line or as part of
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the project file is certainly one way to remove boilerplate. However, it's a controversial feature that often
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draws visceral reactions. We need to discuss this more and figure out if it's a feature we want to have in C#,
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taking into account our increased focus on scripting-like scenarios. It's worth noting that CSX has a limited
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form of this support already, and implementing this in C# proper would bring us one step closer to unifying the
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two dialects.
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#### Conclusion
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Triage to C# 10 for discussion.
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@ -19,9 +19,7 @@
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## Jul 20, 2020
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## Jul 20, 2020
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## Jul 13, 2020
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- [struct private fields in definite assignment](https://github.com/dotnet/csharplang/issues/3431) (Neal/Julien)
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- Triage [championed features](https://github.com/dotnet/csharplang/issues?q=is%3Aopen+is%3Aissue+label%3A%22Proposal+champion%22+no%3Amilestone)
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## Jun 3, 2020
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## Jun 3, 2020
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@ -54,11 +52,17 @@
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# C# Language Design Notes for 2020
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# C# Language Design Notes for 2020
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Overview of meetings and agendas for 2020
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[Overview of meetings and agendas for 2020](https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-07-13.md)
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- Triage open issues
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## Jul 13, 2020
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[C# Language Design Notes for July 13th, 2020]
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## Jul 6, 2020
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## Jul 6, 2020
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[C# Language Design Notes for July 1, 2020](https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-07-06.md)
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[C# Language Design Notes for July 6, 2020](https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-07-06.md)
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- [Repeat Attributes in Partial Members](https://github.com/RikkiGibson/csharplang/blob/repeated-attributes/proposals/repeat-attributes.md) (Rikki)
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- [Repeat Attributes in Partial Members](https://github.com/RikkiGibson/csharplang/blob/repeated-attributes/proposals/repeat-attributes.md) (Rikki)
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- `sealed` on `data` members
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- `sealed` on `data` members
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