I got hit by a car last night. As I was sitting in the emergency room I
realized the answer to Russ Cox's 2011
riddle https://groups.google.com/g/golang-nuts/c/0bcyZaL3T8E - you
disambiguate as you're placing the item in the sum-type/box.
type RW union {
io.Reader
io.Writer
}
mean? Or is it disallowed?
(That would be pretty unfortunate.)
What happens if you have
var r io.Reader = os.Stdin // an *os.File
var rw RW = r* <- io.Reader //this disambiguation is actually not necessary
- if you placed it as an io.Reader it should come out as an io.Reader - but
if the os.Stdin had been placed 'raw' it would have needed a disambiguation
tag. I'm not suggesting syntax (as, inShapeOf... a bunch of syntax is
possible). Basically - it's manually setting the tag on the discriminated
union so there is no ambiguity on retrieval. *
*I haven't written disambiguation syntax - I'd be happy to revisit the
project if someone wants a 'complete' tool to play with - but with that as
an option - I consider simple sum-types solved. The compiler source-code
already has a really solid example that was introduced for generics. I
think the easiest case forward would be to no longer call {type1|type2} an
interface for generics - find a new word - and add disambiguation logic on
insert for the classic Russ Cox case, or use 'box' as a keyword because
it's neat.*
(Apologies - I don't know how to quote properly)
Regarding https://github.com/golang/go/issues/54685 - sigma types. They're
more complex and powerful - they could work if that's what you guys want. I
prefer simple (I think the box concept is simple).
*Question 1, *
*you've made it clear that interfaces can't be types inside a box type,
however, is the opposite true? Can a box type satisfy an interface? **Answer:
*as implemented - boxes only expose the methods to get a concrete type out
of a box - they are not 'the thing itself', they're just a wrapper for a
variable.
*Question 2,*
*is there scope to define methods on a `Box` type? Would defining `func (c
Color) String() string { ... }` satisfy `fmt.Stringer`?**Answer: *Same as
above - boxes are really dumb containers.
On Wednesday, September 3, 2025 at 1:29:33 AM UTC-4 Sandesh Gade wrote:
> First of all, thank you for your effort into this! Impressive stuff. I am
> not a compiler expert, but the repo made it easier to understand the ideas
> you are talking about for someone like me. That being said, my following
> questions are a step towards understanding what is and isn't possible in
> this design?
>
> *Question 1, **you've made it clear that interfaces can't be types inside
> a box type, however, is the opposite true? Can a box type satisfy an
> interface?*
>
> ```go
> type Red struct{}
> func (r Red) String() string { return "red"}
>
> type Green struct{}
> func (g Green) String() string { return "green" }
>
> type Blue struct{}
> func (b Blue) String() string { return "blue"}
>
> type Color box {
> Red
> Green
> Blue
> }
>
> ...
> var c Color
> ...
> ```
>
> Does `c` satisfy fmt.Stringer?
>
> *Question 2,* *is there scope to define methods on a `Box` type? Would
> defining `func (c Color) String() string { ... }` satisfy `fmt.Stringer`?*
> On Monday, 1 September 2025 at 13:50:49 UTC-4 Cliff wrote:
>
>> Hi Gophers!
>>
>> I'm trying to find the right place for this work. I spent a couple of
>> weeks looking at early proposals and dev-team reactions to Discriminated
>> Unions and Enums as well as feedback from surveys and open/closed
>> proposals.
>>
>> I developed box as a fundamental/orthogonal type in the compiler based on
>> that research and I thought maybe it would serve as a discussion point -
>> since it's an implementation that can actually be experimented with.
>>
>> https://github.com/CliffsBits/discriminated_unions_and_enums_for_go
>>
>> I don't think it will break any existing codebases.
>
>
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