Yes, this echos what I stated earlier: "An enum is conceptually the same as you manually typing 1, 2, 3, ... as constants, except the compiler generates the numbers for you automatically" Nice to see that your understanding is growing.
> Taking from your examples, the key point is that a Foo is not a Bar.
I'm not sure that's a useful point. Nobody thinks
class Foo {}
class Bar {}
...are treated as being the same in Java, or, well any language that allows defining types of that nature. That is even the case in Go!
type Foo int
type Bar int
const f Foo = iota
const b Bar = f // compiler error on mismatched types
But what is significant to the discussion about enums is the value that drives the inner union of the class. As in, the numbers that rest beneath SUNDAY, MONDAY, TUESDAY, etc. That's the enum portion.
I don't understand anything more now than I did at the start. It is clear we are talking past each other.
The values of Day are {SUNDAY, ..., SATURDAY} not {0, ..., 6}. We can, of course, establish a 1:1 mapping between those two sets, and the API provides a convenient forward mapping through the ordinal method and a somewhat less convenient reverse mapping through the values static method. However, at runtime, instances of Day are pointers not numbers, and ints outside the range [0, 6] will never be returned by the ordinal method and will cause IndexOutOfBoundsException if used like Day.values()[ordinal].
Tying back to purpose of this thread, Go cannot deliver the same guarantee. Even if we define
type Day int
const (
Sunday Day = iota
// ...
Saturday
)
then we can always construct Day(-1) or Day(7) and we must consider them in a switch statement. It is also trivial to cast to another "enum" type in Go, even if the variant doesn't exist on the other side. This sealed, nonconvertible nature of Java enums makes them "true" enums, which you can call tag-only discriminated unions or whatever if you want, but no such thing exists in Go. In fact, it is not even possible to directly adapt the Java approach, since sealed types of any kind, including structs, are impossible thanks to new(T) being allowed for all types T.
> This sealed, nonconvertible nature of Java enums makes them "true" enums, which you can call tag-only discriminated unions or whatever if you want, and no such thing exists in Go.
It is no secret that Go has a limited type system. In fact, upon release it was explicitly stated that their goal was for it to be a "dynamically-typed language with statically-typed performance", meaning that what limited type system it does have there only to support the performance goals. You'd have to be completely out to lunch while also living under a rock to think that Go has "advanced" types.
But, as before, enums are values. It is not clear why you want to keep going back to talking about type systems. That is an entirely different subject. It may be an interesting one, but off-topic as it pertains to this discussion specifically about enums, and especially not useful when talking in the context of Go which it isn't really intended to be a statically-typed language in the first place.
Yes, this echos what I stated earlier: "An enum is conceptually the same as you manually typing 1, 2, 3, ... as constants, except the compiler generates the numbers for you automatically" Nice to see that your understanding is growing.
> Taking from your examples, the key point is that a Foo is not a Bar.
I'm not sure that's a useful point. Nobody thinks
...are treated as being the same in Java, or, well any language that allows defining types of that nature. That is even the case in Go! But what is significant to the discussion about enums is the value that drives the inner union of the class. As in, the numbers that rest beneath SUNDAY, MONDAY, TUESDAY, etc. That's the enum portion.