Please see below.
https://play.golang.org/p/HXrqLqYIgz
My expected value is:
{"Byte2":0,"Name":"bob"}
But Actual:
{"ByteArray":[0,0,0,0],"Byte2":0,"Name":"bob"}
According to the document (https://golang.org/pkg/encoding/json/)
The empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero.
Therefore, json.Marshall() ignores omitempty-tag, because [0 0 0 0] is not zero-length nor 0 nor nil.
And now, to get the expected value, What should we do?
You'll have to either make ByteArray a slice, or a pointer to array:
type A struct {
ByteArray *[4]byte `json:",omitempty"`
Byte1 byte `json:",omitempty"`
Byte2 byte
Name string `json:",omitempty"`
}
Playground: https://play.golang.org/p/nYBqGrSA1L.
A few options:
Make A an instance of a type with its own MarshalJSON method and implement the behavior you want there (e.g. not including ByteArray if all of its values are zero).
Change the type of ByteArray. []byte would work since it defaults to an empty slice, and *[4]byte would work since it defaults to nil. Including a pointer is a common way of dealing with a field that's only sometimes present in serialization. Of course this does require a little more space, a little more indirection, and a little more GC work.