Ref assignment switch expressions

proposals/ref-assignment-switch-expressions.md

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+# `ref` assignment on `switch` expressions
+
+* [x] Proposed
+* [ ] Prototype: None
+* [ ] Implementation: None
+* [ ] Specification: Started, below
+
+## Summary
+[summary]: #summary
+
+Provide the ability to return `ref` values in `switch` expressions.
+
+## Motivation
+[motivation]: #motivation
+
+The `switch` expression is meant to provide a quicker way to return values based on a given expression, but does not support returning `ref` expressions. This limitation doesn't prevent any harm, and can be lifted.
+
+## Detailed design
+[design]: #detailed-design
+
+A `switch` expression may return a `ref` value. The returning expression, if not a `throw` expression, must be a `ref` expression.
+
+A `switch` expression that returns a `ref` value needs an extra `ref` in front of it when assigned/returned to a `ref` local. The examples below cover this case too. This design aligns with the current design in the ternary operator.
+
+`throw` expressions can still be used normally.
+
+## Examples
+[examples]: #examples
+
+```csharp
+private ref int GetDirectionField(Direction direction) => ref direction switch
+{
+     Direction.North => ref NorthField,
+     Direction.South => ref SouthField,
+     Direction.East => ref EastField,
+     Direction.West => ref WestField,
+     _ => throw new NotImplementedException(),
+};
+
+private void RefSwitchAssignLocal()
+{
+    ref int dimension = ref axis switch
+    {
+        Axis.X => ref X,
+        Axis.Y => ref Y,
+    };
+}
+```
+
+## Drawbacks
+[drawbacks]: #drawbacks
+
+None.
+
+## Alternatives
+[alternatives]: #alternatives
+
+Currently, this may only be achieved with a `switch` statement, or a sequence of `if`-`else` statements.
+
+## Unresolved questions
+[unresolved]: #unresolved-questions
+
+- [ ] Requires LDM review
+- [ ] Should there be a quicker way to denote returning a `ref` to the provided expression by not requiring copying it over for each case?
+
+## Design meetings
+[meetings]: #design-meetings
+
+None.