Switch expression as a statement expression

[gafter]

From dotnet/csharplang#1054

It has been requested that we permit a switch expression to be used as a statement expression. In order to make this work, we'd

Permit its type to be void.
Permit a switch expression to be used as a statement expression if all of the switch arm expressions are statement expressions.
Adjust type inference so that void is more specific than any other type, so it can be inferred as the result type.
Resolution 2018-10-10: Yes! This requires a more precise spec, and it needs to handle a?.M() where M() returns an unconstrained T.

This might not be implemented for C# 8, but it would be good if it were.

[alrz]

Permit a switch expression to be used as a statement expression if all of the switch arm expressions are statement expressions.

Does this recursively applies to itself - meaning we can nest switch expressions in such switch expressions?

e switch { _ => a switch { _ => M() } };

If this is valid, I'll adjust #31812 accordingly.

[gafter]

@alrz Probably yes, but I would not write any IDE code depending on this getting into C# 8 until it is in the language. It may be some time, or it may not make it into C# 8.

[gafter]

Closing pending LDM decisions about what the feature should look like.