Struct field with multiple const types

Question

Say I have a const type and corresponding sub types -

type Animaltype int32 
const ( 
    dogs  Animaltype = iota 
    cats
) 

type dogtype int32 
const ( 
    retriever dogtype = iota 
    whippet 
)

type cattype int32 
const ( 
    siamese cattype = iota 
    tabby 
)

I'd like a structure that holds the animal type and then a field that flexibly holds the subtype

type AnimalCount struct {
  category Animaltype
  subcategory map[dogtype]int32
}

But where I have dogtype for sub category I'd like it to be dogtype or cattype. For eg here I have I would be mapping the subtype to the count of that type

Is this possible in go?

Yes, let me amend that

thefrollickingnerd
– thefrollickingnerd

2025-01-24 03:42:20 +00:00
Commented Jan 24 at 3:42 — thefrollickingnerd
– thefrollickingnerd, Commented Jan 24 at 3:42

Schwern · Accepted Answer · 2025-01-24 03:52:03Z

2

You can do this with a union interface and generics.

// Declare a type which is both cats and dogs
type pettype interface {
    cattype | dogtype
}

// Declare AnimalCount using the union type.
type AnimalCount[T pettype] struct {
  category Animaltype
  subcategory map[T]int32
}

func main() {
    // Instantiate AnimalCount with a concrete type.
    dc := AnimalCount[dogtype]{category: dogs, subcategory: map[dogtype]int32{retriever: 2, whippet: 4}}
    cc := AnimalCount[cattype]{category: cats, subcategory: map[cattype]int32{siamese: 5, tabby: 10}}
    fmt.Println("{}", dc)
    fmt.Println("{}", cc)
}

answered Jan 24 at 3:52

Schwern

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