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encoding/json: cannot use json:"-" to omit a shadowed field of an embedded type. #17016

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bhcleek opened this issue Sep 7, 2016 · 3 comments
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encoding/json: cannot use json:"-" to omit a shadowed field of an embedded type. #17016

bhcleek opened this issue Sep 7, 2016 · 3 comments
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Documentation FrozenDueToAge NeedsFix The path to resolution is known, but the work has not been done.
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Go1.8Maybe

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@bhcleek
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bhcleek commented Sep 7, 2016

What version of Go are you using (go version)?

Go 1.7

What operating system and processor architecture are you using (go env)?

Locally I use:

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/bhcleek/develop/go"
GORACE=""
GOROOT="/usr/local/go"
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/86/4lzvmk8s5mschgm8s7scwxhh0000gn/T/go-build783586116=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"

But the playground also exhibits this behavior.

What did you do?

Embed a struct, shadow one of its fields, and add the json:"-" tag to omit the shadowed field.

https://play.golang.org/p/AaXoSAfRTj

What did you expect to see?

I expected the json to not include a property for the shadowed field.

What did you see instead?

The shadowed field was included in the json.

After consideration, I believe the behavior is correct, because it allows the unmarshal case to work as one would expect, but the documentation doesn't lead one to expect the current behavior for marshalling.
@freeformz
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freeformz commented Sep 7, 2016 •
edited

@bhcleek The Value declared in WrapBar is not shadowing the Value declared in Bar.

Compare this to this to this

@bhcleek
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bhcleek commented Sep 7, 2016

@freeformz I just used the zero values in my example, but your second playground effectively demonstrates the same thing. Notice the properties present in the JSON strings, focusing less on which values are in them. In both my example and your second example, I originally expected the WrapBar json to not include the value property at all. This seems more like a documentation concern than anything else at this point.

@quentinmit quentinmit added this to the Go1.8Maybe milestone Sep 7, 2016
@odeke-em odeke-em changed the title Cannot use json:"-" to omit a shadowed field of an embedded type. encoding/json: cannot use json:"-" to omit a shadowed field of an embedded type. Sep 8, 2016
@quentinmit quentinmit added the NeedsFix The path to resolution is known, but the work has not been done. label Oct 10, 2016
@rsc
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rsc commented Oct 20, 2016

The docs seem clear that - kills the current field, not that it kills any other fields.
If you want to kill the embedded value you can do so by making it unavailable by embedding another value at the same depth.

https://play.golang.org/p/ExZylHohWq

@rsc rsc closed this as completed Oct 20, 2016
@golang golang locked and limited conversation to collaborators Oct 20, 2017
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