Golang隐藏XML父标记（如果为空）

Question

After some trail and error I'd like to share the issue I am dealing with.

I'm populating an struct and convert it to an XML ( xml.Marshal ) As you can see below the Foo example works as expected. The Bar example however creates an empty group1.

So my question is : "How do I prevent Group1 to be generated if there are no children set."

package main

import (
    "fmt"
    "encoding/xml"
)

type Example1 struct{
    XMLName  xml.Name `xml:"Example1"`
    Element1 string   `xml:"Group1>Element1,omitempty"`
    Element2 string   `xml:"Group1>Element2,omitempty"`
    Element3 string   `xml:"Group2>Example3,omitempty"`
}

func main() {
    foo := &Example1{}
    foo.Element1 = "Value1" 
    foo.Element2 = "Value2" 
    foo.Element3 = "Value3" 

    fooOut, _ := xml.Marshal(foo)
    fmt.Println( string(fooOut) )

    bar  := &Example1{}
    bar.Element3 = "Value3"
    barOut, _ := xml.Marshal(bar)
    fmt.Println( string(barOut) )
}

Foo Output :

<Example1>
    <Group1>
        <Element1>Value1</Element1>
        <Element2>Value2</Element2>
    </Group1>
    <Group2>
        <Example3>Value3</Example3>
    </Group2>
</Example1>

Bar Output :

<Example1>
    <Group1></Group1>  <------ How to remove the empty parent value ? 
    <Group2>
        <Example3>Value3</Example3>
    </Group2>
</Example1>

Addition

Additionally i have tried doing the following, but still generates an empty "Group1":

type Example2 struct{
    XMLName  xml.Name `xml:"Example2"`
    Group1   struct{
        XMLName  xml.Name `xml:"Group1,omitempty"`
        Element1 string   `xml:"Element1,omitempty"`
        Element2 string   `xml:"Element2,omitempty"`
    }
    Element3 string   `xml:"Group2>Example3,omitempty"`
}

The full code can be found here : http://play.golang.org/p/SHIcBHoLCG . example to

EDIT : Changed the golang example to use MarshalIndent for readability

Edit 2 The example from Ainar-G Works good for hiding the empty parent, but Populating it makes it a lot harder. "panic: runtime error: invalid memory address or nil pointer dereference"

Answer 1

Example1 doesn't work because apparently the ,omitempty tag only works on the element itself and not the a>b>c enclosing elements.

Example2 doesn't work because ,omitempty doesn't recognise empty structs as empty. From the doc:

The empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero.

No mention of structs. You can make the baz example work by changing Group1 to a pointer to a struct:

type Example2 struct {
    XMLName  xml.Name `xml:"Example1"`
    Group1   *Group1
    Element3 string `xml:"Group2>Example3,omitempty"`
}

type Group1 struct {
    XMLName  xml.Name `xml:"Group1,omitempty"`
    Element1 string   `xml:"Element1,omitempty"`
    Element2 string   `xml:"Element2,omitempty"`
}

Then, if you want to fill Group1, you'll need to allocate it separately:

foo.Group1 = &Group1{
    Element1: "Value1",
}

Example: http://play.golang.org/p/mgpI4OsHf7