On Saturday, June 20, 2020 at 3:08:42 PM UTC-4, David Finkel wrote:
>
>
>
> On Sat, Jun 20, 2020 at 11:03 AM T L <tapi...@gmail.com <javascript:>>
> wrote:
>
>>
>>
>> On Saturday, June 20, 2020 at 10:21:56 AM UTC-4, Axel Wagner wrote:
>>>
>>> I would assume it's
>>>
>>> type MapConstraint(type K comparable, V interface{}) interface {
>>> type map[K]V
>>> }
>>>
>>> func F(type M MapConstraint(K, V), K comparable, V interface{}) (m M) {
>>> }
>>>
>>> Note that you are under no obligation to make use of a type-parameter if
>>> you don't need it.
>>>
>>
>> I don't very understand this. Can a slice value be used as the argument
>> of the F function?
>>
> For that, I think you'd need the interface to be:
> type MapSliceConstraint(type K comparable, V interface{}) interface {
> type map[K]V, []V
> }
>
> I'm not quite sure how to eliminate the useless K type-param for slices,
> though.
>
> Note: the relevant draft design section is:
> https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md#type-parameters-in-type-lists
>
> Here's an almost working example:
> https://go2goplay.golang.org/p/qcdfl0tuHlb
>
> It looks like there's a bug in the type-parameter constraint checking
> because in the above example code, I get:
>
> type checking failed for main
>
> prog.go2:11:39: K does not satisfy comparable
>
> This, despite the type parameter definition literally requiring that K be
> comparable:
> func genLen(type T MapSliceConstraint(K, V), K *comparable*, V
> interface{})(collection T) int {
> return len(collection)
> }
> (example without a main() to reduce clutter:
> https://go2goplay.golang.org/p/1gqiYuDELuI)
>
Thanks for making this example.
However, it almost reach my upper limit understanding ability to get the
implementation.
I looks some bad practices in using C++ template.
Is it good to add a Kind list constraint? For example,
type MapOrSlice interface {
kind map, []
}
>
>>
>>>
>>> On Sat, Jun 20, 2020 at 4:14 PM T L <tapi...@gmail.com> wrote:
>>>
>>>> I mean I don't care about the element and key types of the parameter
>>>> type.
>>>>
>>>> For a simple example, I want to define a generic function which prints
>>>> the length of a container (do do some other things):
>>>>
>>>> func Print(type T Container) (v T) {
>>>> // ... do some things
>>>>
>>>> fmt.Println(len(v))
>>>>
>>>> // ... do some things
>>>> }
>>>>
>>>> On Saturday, June 20, 2020 at 9:16:39 AM UTC-4, T L wrote:
>>>>>
>>>>> .
>>>>>
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>>>> .
>>>>
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>
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