Array with different types or object inheritance

Question

I'm programming an xml response API in golang. Following the examples in the xml documentation it's pretty easy to create the xml giving them attributes and more.

The thing is that I need multiple tags under the same name and in different order.

<block>
    <tag1>A Value1</tag1>
    <tag2>B Value1</tag2>
    <tag1>A Value2</tag1>
</block>

By creating a structure like

type Tag1 struct {
    Value string `xml:",chardata"`
}
type Tag2 struct {
    Value string `xml:",chardata"`
}
type Block struct {
    XMLName   xml.Name `xml:"block"`
    Tags1     []Tag1   `xml:"tag1"`
    Tags2     []Tag2   `xml:"tag2"`
}

I achieved this xml:

<block>
    <tag1>A Value1</tag1>
    <tag1>A Value2</tag1>
    <tag2>B Value1</tag2>
</block>

That's due to the array type inside the block definition. What I want, is a way to define that array type as an interface to inherit the two Tag types. Like this

type Block struct {
    XMLName   xml.Name `xml:"block"`
    Tags      []Tags   `xml:"tags"`
}
type (Tags t) Tag1 struct{
    Value string `xml:",chardata"`
}
type (Tags t) Tag2 struct{
    Value string `xml:",chardata"`
}

This way I could define the order of appearance in xml by the order of appending like

a1 := Tag1{"A Value1"}
b1 := Tag2{"B Value1"}
a2 := Tag1{"A Value2"}

arr :=  []Tags{}
arr = append(arr,a1)
arr = append(arr,b1)
arr = append(arr,a2)

v.Tags = arr

I've made some reading and I'm trying to avoid to implement the marshaling function used inside the xml package. Any help is appreciated, thanks.

There is no inheritance in Go. You could make `Tags` a slice of an interface type (either `interface{}` or something more specific) and do it that way. Types do not specify the interface(s) they want to implement. — Adrian, Jan 25 '18 at 22:10

score 0 · Accepted Answer · answered Jan 25 '18 at 22:30

I solved it differently. I just wasn't looking for the right approach. This question described what I needed. By defining the XMLName xml.Name value in the Tag1 struct, I could define the name of the tag programmatically. And then just include the different Tags value with the old friend []interface{} type.

type Tag1 struct {
    XMLName xml.Name
    Value   string `xml:",chardata"`
}
type Block struct {
    XMLName xml.Name `xml:"block"`
    Tags    []interface{}
}
a1 := Tag1{XMLName: xml.Name{Local: "tag1"}, Value: "A Value1"}
a2 := Tag1{XMLName: xml.Name{Local: "tag1"}, Value: "A Value2"}
b1 := Tag2{XMLName: xml.Name{Local: "tag2"}, Value: "B Value1"}

v := &Block{}
v.Tags = []interface{}{a1, b1, a2}

Check this example out to give it a play.

Array with different types or object inheritance

1 Answers1