Hi Josh,
thanks a lot. It helps me to understand interface in go.
Am Sa., 12. Jan. 2019 um 00:08 Uhr schrieb Josh Humphries <
jh...@bluegosling.com>:
> On Fri, Jan 11, 2019 at 5:59 PM Xinhu Liu <xinhu.li...@gmail.com> wrote:
>
>> Hi Ian,
>>
>> thanks for your reply.
>>
>> After reading and experimenting a lot I think I understand the slight
>> differences between nil and interface{} with nil value.
>>
>> The only thing I find confusing is that interface{}(nil) == nil returns
>> true.
>>
>
> In that context, they are the same thing -- the nil interface. In fact
> SomeInterface(nil)
> == interface{}(nil) is also true -- the values are both the nil interface.
> (The nil identifier is quite overloaded in Go since it can also indicate a
> nil pointer, a nil map, a nil slice, a nil function, or a nil channel,
> depending on context).
>
> The issue at hand is that reflect.ValueOf(nil) does *not* give you an
> instance with type interface{} and value nil -- it gives you a zero-value
> (e.g. invalid) instance. This is because reflect.ValueOf returns the
> *concrete* type and value of the input value, but nil interface has no
> concrete type or value. So, in order to get a reflect.Value of type
> interface{} and nil value, you have to go through some hoops.
>
>
>>
>> (The reason why I use reflect on interface is that I want to operate
>> slice with different element types, like []interface{}, []int and so on.)
>>
>> Best regards,
>> Xinhu
>>
>> Am Fr., 11. Jan. 2019 um 01:39 Uhr schrieb Ian Lance Taylor <
>> i...@golang.org>:
>>
>>> On Thu, Jan 10, 2019 at 3:40 PM <xinhu.li...@gmail.com> wrote:
>>> >
>>> > I want to append a nil value using reflect.Append(), but I got a
>>> panic: reflect: call of reflect.Value.Set on zero Value.
>>> >
>>> > This is my code.
>>> >
>>> > s := make([]interface{}, 10)
>>> > v := reflect.ValueOf(nil)
>>> > reflect.Append(reflect.ValueOf(s), v)
>>> >
>>> > So is there a way i can append nil? Currently I do this as workaround:
>>> >
>>> > s := make([]interface{}, 10)
>>> > s0 := make([]interface{}, 1)
>>> > r := reflect.AppendSlice(reflect.ValueOf(s), reflect.ValueOf(s0))
>>> >
>>> > It works but I think there must be a better way.
>>>
>>> First you have to clearly distinguish between nil, an uninitialized
>>> value with no type, and the value interface{}(nil), which is an
>>> uninitialized value of type interface{}. You want the latter. Then,
>>> it's always a bit awkward to work with interface types with the
>>> reflect package, because the reflect package naturally tries to look
>>> for the value stored in the interface type, whereas you actually want
>>> the interface type.
>>>
>>> Here is one way to do it:
>>>
>>> https://play.golang.org/p/Qt5-AmYa9Mk
>>>
>>> Ian
>>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "golang-nuts" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to golang-nuts+unsubscr...@googlegroups.com.
>> For more options, visit https://groups.google.com/d/optout.
>>
>
--
You received this message because you are subscribed to the Google Groups
"golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to golang-nuts+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
