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# Enums
Goals:
* Better syntax for passing constructor parameters when defining enum constants
* Resolve issues with annotation syntax for enum constants
## Example
Simple enum:
``` kotlin
enum class Foo {
A
B
C {
override fun foo() { ... }
}
open fun foo() {}
}
```
Enum with constructor:
``` kotlin
enum class Foo(val s: String) {
A("a")
B("b")
C("c") {
override fun foo() { ... }
}
open fun foo() {}
}
```
Issues
* Enum literals syntax clash with annotation syntax
* Option 1.1: Forbid short annotation syntax in enums. **downside**: cannot annotate functions/properties/classes in this enum
* Option 1.2: Add a separator between enum constants and members, and forbid short annotation syntax only on enum entries themselves. **downside**: separator is not intuitive, hard to think of when doing this for the first time (the error message will be rather clear and instructive, though)
* Option 1.3: prefix each entry with a soft-keyword, e.g. `entry`. **downside**: verbosity
* Option 1.4 **chosen**: Add a semicolon separator after the last enum constant, **and** a comma separator between different enum constants.
* How do we specify other supertypes for a constant (if any)
* Option 2.1 **chosen**: Leave unsupported, use cases are very few, and Java does not support it
* Option 2.2: `A("s"): OtherType`
Example for option 1.4:
``` kotlin
enum class Foo(val s: String) {
A("a"), // semicolon CAN NOT be used here!
B("b"), // comma is MANDATORY after each enum constant except the last one
C("c") {
override fun foo() { ... }
}; // semicolon is MANDATORY here, even if no member follows
open fun foo() {}
}
```
Notes:
* Almost no overhead in the most common case of no members at all: `enum class E {A, B, C; }
* Clear error message: if the parser sees no semicolon after the last constant:
* it reports an error saying "There must be a semicolon after the last enum entry", which is rather instructive
* a quick fix can even guess the right position for the semicolon most of the time
* Today, there's no way of naming an enum entry `public` (or any other soft-keyword used as a modifier), which is unfortunate
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