On Jan 20, 2019, at 16:36, Burak Serdar <bser...@ieee.org> wrote:
>
>> On Sun, Jan 20, 2019 at 2:32 PM 伊藤和也 <kazya.ito.dr...@gmail.com> wrote:
>>
>> type a interface{
>> m()
>> }
>>
>> type abc int
>> func (abc) m() {}
>>
>> func main() {
>> var v a
>> v.m()
> ^^^^^^
>
> v is nil. It is declared but never assigned a value. You are
> dereferencing v to call m, causing nil ptr dereference.
Importantly, v is of type a, which is an interface; it has to be dereferenced
in some sense in order to get its type information in order to figure out what
m() method to call.
If you’d made v of type *abc (and m() was a method for type *abc, not abc),
this would actually be valid and would execute, but the instance pointer passed
to m() would be nil. Sometimes that’s actually something you want to do/handle,
though I would argue it’s fairly rare and more often it’s something you would
want to check as an error case.
- Dave
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