Yup, doesn't quite make sense to me that Error() is called if it's an
embedded struct and not when it's a struct field.
See https://play.golang.org/p/Vp6Y-RETWZ
On Friday, July 15, 2016 at 2:03:25 PM UTC-7, Thorsten von Eicken wrote:
>
> You're probably correct, see this:
>
> package main
>
> import (
> "fmt"
> )
>
> type MyError struct{ error }
> type MyError2 struct {
> foo int
> err error
> }
>
> func main() {
> err := MyError{}
> fmt.Printf("%%#v %#v\n", err)
> fmt.Printf("%%+v %+v\n", err)
> fmt.Printf("%%v %v\n", err)
>
> err2 := MyError2{}
> fmt.Printf("%%#v %#v\n", err2)
> fmt.Printf("%%+v %+v\n", err2)
> fmt.Printf("%%v %v\n", err2)
>
> var rr error
> fmt.Printf("%%#v %#v\n", rr)
> fmt.Printf("%%+v %+v\n", rr)
> fmt.Printf("%%v %v\n", rr)
> }
>
> %#v main.MyError{error:error(nil)}
> %+v %!v(PANIC=runtime error: invalid memory address or nil pointer
> dereference)
> %v %!v(PANIC=runtime error: invalid memory address or nil pointer dereference)
> %#v main.MyError2{foo:0, err:error(nil)}
> %+v {foo:0 err:<nil>}
> %v {0 <nil>}
> %#v <nil>
> %+v <nil>
> %v <nil>
>
>
> It's only if the error is embedded that it panics.
> Playground: https://play.golang.org/p/TeNVj96zxr
>
> On Friday, July 15, 2016 at 1:44:01 PM UTC-7, Matt Harden wrote:
>>
>> I think MyError has the Error method, which %v will use but %#v will not.
>> Then it panics because it's trying to call error(nil).Error().
>>
>> On Fri, Jul 15, 2016, 13:22 Thorsten von Eicken <t...@rightscale.com>
>> wrote:
>>
>>> I was surprised to see Printf %v panic on a struct that %#v prints fine.
>>> Is this expected / intentional / as designed?
>>>
>>> Test case:
>>> package main
>>>
>>> import (
>>> "fmt"
>>> )
>>>
>>> type MyError struct{ error }
>>>
>>> func main() {
>>> err := MyError{}
>>> fmt.Printf("%%#v %#v\n", err)
>>> fmt.Printf("%%+v %+v\n", err)
>>> fmt.Printf("%%v %v\n", err)
>>> }
>>>
>>> Output:
>>>
>>> %#v main.MyError{error:error(nil)}
>>> %+v %!v(PANIC=runtime error: invalid memory address or nil pointer
>>> dereference)
>>> %v %!v(PANIC=runtime error: invalid memory address or nil pointer
>>> dereference)
>>>
>>>
>>> Playground: https://play.golang.org/p/B5FeWMryN0
>>>
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