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
axel.wa...@googlemail.com 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 <santhos...@gmail.com>
> 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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