Thank you for the info. The purpose of using generics is to avoid reflect
or interface{}, at least for me :-)
在2024年4月8日星期一 UTC+8 18:35:18<Axel Wagner> 写道：
> Yes, the *underlying type* of Class is `byte`, but the type-switch checks
> if the dynamic type is *exactly* `byte`.
> The only way, currently, to implement the kind of check you want is to use
> reflect:
>
> switch rv := reflect.ValueOf(v); rv.Kind() {
> case reflect.Uint8: // byte
> v := uint8(rv.Uint())
> // ...
> }
>
> Though you might be interested in #45380
> <https://github.com/golang/go/issues/45380>, which would be able to solve
> this without reflect.
>
> On Mon, Apr 8, 2024 at 11:04 AM Xiangrong Fang <xrf...@gmail.com> wrote:
>
>> I wrote a TLV handling package: go.xrfang.cn/tlv
>> <https://pkg.go.dev/go.xrfang.cn/tlv>, and encountered problem with type
>> checking. Problematic code below:
>>
>> 1. The "Set" function in side tlv package:
>>
>> package tlv
>>
>> type (
>> ValueType interface {
>> string | []byte | ~float32 | ~float64 |
>> ~int8 | ~int16 | ~int32 | ~int64 |
>> ~uint8 | ~uint16 | ~uint32 | ~uint64
>> }
>> Prop map[byte][]byte
>> )
>>
>> func Set[T ValueType](p Prop, tag byte, val T) Prop {
>> ... ...
>> switch v := any(val).(type) {
>> case string:
>> ... ...
>> default:
>> fmt.Printf("tlv.Set: '%T' not supported!\n", val)
>> }
>> ...
>> }
>>
>> 2. event.go, which uses tlv:
>>
>> package event
>>
>> import (
>> "go.xrfang.cn/tlv"
>> )
>>
>> type (
>> Class byte
>> Event struct {
>> tlv.Prop
>> }
>> )
>>
>> const (
>> TagClass = 3
>> )
>>
>> func (e *Event) WithClass(cls Class) *Event {
>> (*e).Prop = tlv.Set((*e).Prop, TagClass, cls)
>> return e
>> }
>>
>> The problem is, while the Class type is based on "byte", it should be
>> accepted by tlv.Set(), which is the case (there is no compiler error). But
>> when the code is running, it printed error message: tlv.Set: 'event.Class'
>> not supported!
>>
>> --
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>> .
>>
>
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