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Mads Torgersen 2017-05-30 17:04:11 -07:00
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20
meetings/2017/LDM-2017-03-28.md
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@ -1,27 +1,28 @@
# C# Language Design Notes for Mar 28, 2017
***Raw notes, yet to be cleaned up - read at your own peril***
## Agenda
Design remaining 7.1 features
Design some remaining 7.1 features
1. Fix pattern matching restriction with generics
2. Better best common type
# permit match of expr of type T:base with derived
# Fix pattern matching restriction with generics
Today `x as T` is allowed if
1. there is a reasonable relationship between the left and right type, or
2. one of them is an open type
But for the `is` operator we don't have 2. That means that we can't always replace uses of `as` followed by null check with an `is` with a type pattern.
But for the `is` operator we don't have the second. That means that we can't always replace uses of `as` followed by null check with an `is` with a type pattern.
Also, the restrictions are supposed to rule out only obviously useless cases, whereas some of these are demonstrably useful.
Let's allow it, look again if there are unexpected problems.
# Better common type
# Better best common type
Best common type should combine a value type with null literal to get a nullable value type.
@ -33,7 +34,7 @@ b1 ? 1 : (b2 ? null : (b3 ? 2 : default)); // default is 0
b1 ? 1 : (b2 ? default : (b3 ? 2 : null)); // default is null
```
This is weird, but fine.
This is weird, but fine:
``` c#
M(1, default, null); // int?
@ -44,8 +45,3 @@ Next step is trying to spec it. It's a bit complicated.
``` c#
M(myShort, myNullableInt, null); Should continue to infer int? , not short?
```
# Lambda discards
# Mix
# Expr vars in initializers

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meetings/2017/README.md
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@ -122,3 +122,11 @@ Discussion of default interface member implementations, based on [this guided to
11. Static non-virtual members
12. Accessibility levels
13. Existing programs
## Mar 28, 2017
[C# Language Design Notes for Mar 28, 2017](LDM-2017-03-28.md)
Design some remaining 7.1 features
1. Fix pattern matching restriction with generics
2. Better best common type