Java 14 switch expression multi-statement support

[paulirwin]

With #63, basic support for Java 14 switch expressions was added. There is a multi-statement form of switch expressions that is not yet supported, using the yield keyword to yield the expression from the block of statements.

See: https://docs.oracle.com/en/java/javase/14/language/switch-expressions.html#GUID-BA4F63E3-4823-43C6-A5F3-BAA4A2EF3ADC__GUID-4900EB1C-3832-4CB8-ACAE-A87675260B75

Example:

    Day day = Day.WEDNESDAY;
    int numLetters = switch (day) {
        case MONDAY:
        case FRIDAY:
        case SUNDAY:
            System.out.println(6);
            yield 6;
        case TUESDAY:
            System.out.println(7);
            yield 7;
        case THURSDAY:
        case SATURDAY:
            System.out.println(8);
            yield 8;
        case WEDNESDAY:
            System.out.println(9);
            yield 9;
        default:
            throw new IllegalStateException("Invalid day: " + day);
    };
    System.out.println(numLetters);

We might be able to half-translate this into IIFE-style lambda functions, with a Func<SPECIFY_ME> type where the user must replace SPECIFY_ME with whatever the appropriate type is (which might not be obvious syntactically i.e. if you use var).

This is ugly but it might work in most cases. A warning should be emitted whenever we have to do this. Also note return from the lambda instead of yield.

For example:

    Day day = Day.WEDNESDAY;
    int numLetters = day switch {
        MONDAY or FRIDAY or SUNDAY => ((Func<SPECIFY_ME>)(() => 
        {
            Console.WriteLine(6);
            return 6;
        }))(),
        ...
    };

[OJacot-Descombes]

There is a Proposal: Block-bodied switch expression arms #3037 which will probably be scheduled soon for a C# language design meeting.

[ziaulhasanhamim]

Switch expressions are incomplete if you can't have multiple lines because you usually need multiple lines. Having blocked-bodied expression arms makes total sense.