I change it to following:
type JSON struct{ Val interface{} }
thanks
Santhosh
On Tuesday, February 16, 2021 at 1:58:58 PM UTC+5:30 [email protected] wrote:
> You need you Json type to be a concrete type, e.g. (if the underlying type
> is a string)
>
> type Json string
>
> Then users can try to assert that what they get is of concrete type Json
>
> Cheers,
>
> Arnaud
>
> On Tue, 16 Feb 2021, 08:20 Santhosh Kumar T, <[email protected]> wrote:
>
>> I am not using either json.Marshaler or json.Unmarshaller
>>
>> my project implements mysql binlog replication protocol
>>
>> i have a method: fn nextRow() []interafce{}
>> which returns values in row as slice.
>> the row might contain VARCHAR and JSON type columns in mysql table
>> definition
>> if actual json value for a row is string, then nextRow() return a slice
>> containing two strings
>> to distinguish i am trying to returns []interface{}{"value1",
>> Json("value2")}
>> but this seems does not solve the issue, since user of my library cannot
>> check if it is json value or not
>>
>> thanks
>> Santhosh
>>
>> On Tuesday, February 16, 2021 at 1:32:07 PM UTC+5:30
>> [email protected] wrote:
>>
>>> An interface type-assertion asserts that the dynamic value in the
>>> interface (in this case it's `string`) implements the interface you are
>>> asserting (in this case `myinterface`). As `myinterface` has no methods,
>>> every value implements that interface.
>>>
>>> In general, a type-assertion will assert things about the dynamic value
>>> stored in an interface. In that code, the dynamic value is `string` *either
>>> way*. In one case, you assign a `string` to `interface{}`, in the other you
>>> assign a `string` to `myinterface`. But both will ultimately store a
>>> `string`. That's also why your first case, using `mystring` works as
>>> expected - in that case, the dynamic type is `string` in one case and
>>> `mystring` in the other (note that the dynamic type is *always* a "concrete
>>> type", not an interface).
>>>
>>> In general, ways to get around this is to either a) not use an
>>> interface, or b) give that interface a method only specific types
>>> implement, or c) store a `*myinterface` - it's a pointer, not an interface,
>>> thus a concrete type, which can be distinguished. However, in your case,
>>> neither of these strategies would likely be fruitful. The `json` package
>>> needs to know how to store the values it decodes and it won't be able to,
>>> if it doesn't have a concrete type or a `json.Unmarshaler`.
>>>
>>> So in your specific case, you might want to consider using something like
>>>
>>> type struct {
>>> s string
>>> n int64
>>> isString bool
>>> }
>>>
>>> and have that implement `json.Marshaler` and `json.Unmarshaler`.
>>>
>>> On Tue, Feb 16, 2021 at 8:47 AM Santhosh Kumar T <[email protected]>
>>> wrote:
>>>
>>>> I have a function call nextRow which returns []interface{}
>>>>
>>>> i want to add support for json, since json value can be string, number
>>>> which conflicts
>>>> with native types, i used following:
>>>> type Json interface{}
>>>> and returning json values as:
>>>> return Json(v)
>>>> but in type checking it fails.
>>>>
>>>> i extract minimal code to explain my issue:
>>>> https://play.golang.org/p/AAbeOzH-SHE
>>>>
>>>> in the above example, it prints: v3 is myinterface
>>>> but v3 is regular interface{} not of type myinterface
>>>>
>>>> could someone help in resolving the issue.
>>>> Is this expected behavior. what can i do to workaround if so
>>>>
>>>> thanks
>>>> Santhosh
>>>>
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