Add LDM notes for May 6, 2020

meetings/2020/LDM-2020-05-06.md

@@ -0,0 +1,79 @@
+# C# LDM for May 6, 2020
+
+## Agenda
+
+1. `if (e is not int i)`
+2. Target-typed conditional
+3. Extension GetEnumerator
+4. `args` in top-level programs
+
+## Discussion
+
+### `if (e is not int i)`
+
+https://github.com/dotnet/csharplang/issues/3369 
+
+There are broader features that we'd to consider here as well, for instance allowing
+some declarations below `or` patterns. However, this should be compatible with broader
+changes and is easy to implement right now.
+
+#### Conclusion
+
+Accepted for C# 9. Further elaborations will be considered, assuming the schedule could
+accept it.
+
+### Target-typed conditional
+
+We still unfortunately have a breaking change here with
+
+```C#
+M(b ? 1 : 2, 1); // calls M(long, long) without this feature; ambiguous without this feature
+
+M(short, short);
+M(long, long);
+```
+
+As always, breaking changes are very worrying, unless we are confident that almost no real-world
+code would be broken. If the breaking change results in an ambiguity instead of silent different
+codegen, that is substantially better, as people would at least know that the compiler changed
+behavior. At the moment, we only think that this change could result in new ambiguities, not
+different behavior.
+
+#### Conclusion
+
+We'll do some more investigation, try to find code that would be broken, and see if we can accept
+the change.
+
+### Extension GetEnumerator
+
+https://github.com/dotnet/roslyn/issues/43147 
+
+Conclusions:
+
+No objections to the proposals as written.
+
+### `args` in Top-Level programs
+
+If the top-level statements are logically inside a `Main` method, it would be very useful to have
+access to the command line arguments for the program. You can access these via
+`Environment.GetCommandLineArgs()`, but it's unfortunate that this is both different from the
+APIs in Main, and `Environment.GetCommandLineArgs()` includes the program name, and `args` in
+Main does not.
+
+If we want to do something, we could have a magic variable named `args` (similar to `value` in
+setters) or a property in the framework called `Args` (e.g. `Environment.Args`).
+
+In favor of the property, fewer language-level changes means fewer things that people have to
+learn.
+
+In favor of the `args` magic variable, it's simpler to use than a property (since the property
+would either have to qualified with a type name, or a `using static` would have to be added) and
+a language feature for the inputs (command line args) mirrors the language feature for the output
+(returning an `int` that turns into the process exit code).
+
+#### Conclusion
+
+We'll go with the `args` magic variable. We still need to decide on the scope: either equivalent
+to top-level locals, which are visible in all files but inaccessible, or only in scope in
+top-level statements. If we make it visible in all files we would only add the variable if there
+is at least one top-level statement in the program.

meetings/2020/README.md

@@ -30,13 +30,6 @@
 - Record Monday (Andy, Jared, Mads)
     - https://gist.github.com/MadsTorgersen/3fb6b7461e211c8458044ad5115f2117 Primary constructors and records (Mads)
 
-## May 6, 2020
-
-- Continued: Target-typing ?: when the natural type isn't convertible to the target type. (Neal)
-- https://github.com/dotnet/csharplang/issues/3369 Allow `if (x is not string y)` pattern.  (Cyrus + Neal)
-- https://github.com/dotnet/roslyn/issues/43147 Open issues in extension `GetEnumerator` (Fred)
-- https://github.com/dotnet/csharplang/blob/master/proposals/Simple-programs.md Args in top-level programs (Aleksey, Mads)
-
 ## April 29, 2020
 
 - Design review
@@ -65,6 +58,15 @@
 
 Overview of meetings and agendas for 2020
 
+## May 6, 2020
+
+[C# Language Design Notes for May 6, 2020](https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-05-06.md)
+
+1. Target-typing ?: when the natural type isn't convertible to the target type.
+1. Allow `if (x is not string y)` pattern.
+1. Open issues in extension `GetEnumerator`
+1. Args in top-level programs
+
 ## May 4, 2020
 
 [C# Language Design Notes for May 4, 2020](https://github.com/dotnet/csharplang/blob/master/meetings/2020/LDM-2020-05-04.md)