Thank you. Yeah, that seems overly complicated. I can allocate interior to
the generic object, but I can't use pointer-receiver methods, which is fine
in my case, I'll just adjust the interior manually.
Thank you.
On Saturday, January 13, 2024 at 1:50:17 PM UTC-6 Axel Wagner wrote:
> The way to do that is to add another level of indirection (as everything
> in Software Engineering):
>
> type Namer[T any] interface {
> *T
> SetName(name string)
> }
> func WithName[T any, PT Namer[T]](name string) T {
> var v T
> PT(&v).SetName(name)
> return v
> }
>
> I will say, though, that it's not unlikely that you'll be happier if you
> don't do this and instead accept a plain interface value and let the caller
> allocate the value and pass in a pointer. But if you want to do it, this is
> the way.
>
> On Sat, Jan 13, 2024 at 8:10 PM Daniel Theophanes <kard...@gmail.com>
> wrote:
>
>> I have a situation where I would like to create a type, then set a
>> property on it within a container. To set the type, I envisioned using a
>> method "SetName" which would need to take a pointer receiver: (goplay share
>> is down right now so I'll post inline:
>> type Namer interface {
>> SetName(name string)
>> }
>>
>> I wish to create a new Namer type as well, ideally without using reflect.
>> If I use [*Ob ] as the type parameter, that works, but then `new(T)`
>> returns `**Ob`, which I can deference to get `*Ob`, but then the value is
>> nil (Ob isn't created).
>>
>> I'm working around this, but it surprised me, the interaction of a
>> pointer receiver interface type constraint and then I can't create the
>> desired type.
>>
>> ```
>> package main
>>
>> import "fmt"
>>
>> func main() {
>> ar := NewAppResult()
>> fmt.Printf("AR: %#v\n", *ar)
>> ar.Observation.Get("X1")
>> }
>>
>> type Ob struct {
>> Gene string
>> Value string
>> }
>>
>> func (o *Ob) SetName(name string) {
>> // o is nil and this will panic.
>> o.Gene = name
>> }
>>
>> type Namer interface {
>> SetName(name string)
>> }
>>
>> type OrderedLookup[T Namer] struct {
>> List []T
>> lookup map[string]T
>> }
>>
>> func (ol *OrderedLookup[T]) Get(name string) T {
>> v, ok := ol.lookup[name]
>> if !ok {
>> var v T // T is a pointer, new(T) creates **Ob, but I cant use generic
>> type of [Ob] because then Namer
>> v.SetName(name)
>> ol.lookup[name] = v
>> ol.List = append(ol.List, v)
>> }
>> return v
>> }
>>
>> type AppResult struct {
>> Observation *OrderedLookup[*Ob]
>> }
>>
>> func NewAppResult() *AppResult {
>> return &AppResult{
>> Observation: &OrderedLookup[*Ob]{},
>> }
>> }
>> ```
>>
>>
>>
>> --
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>> <https://groups.google.com/d/msgid/golang-nuts/8d0c816c-c332-4b44-87e3-9259ad173afcn%40googlegroups.com?utm_medium=email&utm_source=footer>
>> .
>>
>
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