This is a bug that has been fixed on Go tip by
https://go-review.googlesource.com/c/go/+/65550.
On 23 January 2018 at 00:45, Josh Humphries <jh...@bluegosling.com> wrote:
> I think have misspoken. Even though the field's name appears exported via
> reflection (it has a name that starts with a capital letter), attempting to
> use the reflect.Value's SetInt method panics, indicating that the field was
> obtained using an unexported field. So the encoding/json package is thus
> consistent with that in that it ignores unexported fields.
>
> It is still not obvious from the spec what should be happening. I would
> expect it to be exported due to the resolved field name. But if it is
> unexported because the compiler resolves the alias first, then I would
> expect a compiler error because the four fields all resolve to the same
> name. The spec states this is not allowed:
>
> The following declaration is illegal because field names must be unique in a
> struct type:
>
> struct {
> T // conflicts with embedded field *T and *P.T
> *T // conflicts with embedded field T and *P.T
> *P.T // conflicts with embedded field T and *T
> }
>
> So it is possible that this is not a bug in the encoding/json package but in
> the compiler.
>
> ----
> Josh Humphries
> jh...@bluegosling.com
>
> On Mon, Jan 22, 2018 at 7:28 PM, Josh Humphries <jh...@bluegosling.com>
> wrote:
>>
>> I think that is expected, and it is the JSON marshaling that is surprising
>> (and erroneous).
>>
>> If it were expected that the embed field names resolved to the alias
>> target type name, it would instead be a compiler error since the compiler
>> does not allow embedded types that would result in name collisions. Using
>> reflection, one can see the fields are named just as in your example, after
>> the type aliases, not its underlying type name. The bug is that JSON
>> marshaling is not looking at the field name and instead looking directly at
>> the field type name (which, in this case, has been resolved to int).
>>
>> ----
>> Josh Humphries
>> jh...@bluegosling.com
>>
>> On Mon, Jan 22, 2018 at 5:58 PM, Dan Kortschak
>> <dan.kortsc...@adelaide.edu.au> wrote:
>>>
>>> This is sort of surprising though: https://play.golang.org/p/mjfkzIqAo_b
>>>
>>> On Mon, 2018-01-22 at 10:20 -0800, C Banning wrote:
>>> > From the Language Specification -
>>> >
>>> > A field declared with a type but no explicit field name is called an
>>> > *embedded
>>> > field*. An embedded field must be specified as a type name T or as a
>>> > pointer to a non-interface type name *T, and T itself may not be a
>>> > pointer
>>> > type. The unqualified type name acts as the field name.
>>> >
>>> > // A struct with four embedded fields of types T1, *T2, P.T3 and
>>> > *P.T4
>>> > struct {
>>> > T1 // field name is T1
>>> > *T2 // field name is T2
>>> > P.T3 // field name is T3
>>> > *P.T4 // field name is T4
>>> > x, y int // field names are x and y
>>> > }
>>> >
>>> >
>>> > From the encoding/json#Marshal documentation -
>>> >
>>> > Struct values encode as JSON objects. Each exported struct field
>>> > becomes a
>>> > member of the object, using the field name as the object key, unless
>>> > the
>>> > field is omitted for one of the reasons given below.
>>> >
>>>
>>> --
>>> 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.
--
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.
