XML-Parser default values

[kuli...@gmail.com]

I want to parse an xml file.

It has a number of "submesh" tags.

Each submesh tag has the optional attribute "usesharedvertices" which defaults to true, if the parameter is omitted.

When parsing like this

var result MyXMLClass

err := xml.Unmarshal(data, &result)

 it defaults to false.

I can't set all values to true beforehand however, since i don't know how many submesh tags there will be.

Is there an easy way like

type Submesh struct {

    UsesSharedVertices bool `xml:"usesharedvertices;default:true"`

}

which the xml-Parser understands and uses?

Or how do i solve this? 

[Kuli Kugelschreiber]

Since this functionality didn't seem available, I implemented it myself.

Example of the usage:

type Foo struct { 

      Bar bool `xml:"bar,attr" default:"true"`
}

 

Whenever the attribute bar is ommited, it will be set to true by the parser.
This works for any native type (and pointers).

In case anyone needs it, here is what i did.

(Changes in the following files (as of golang 1.1))

encoding/xml/typeinfo.go

Added field default Value to type fieldInfo:

type fieldInfo struct {

idx     []int

name    string

xmlns   string

defaultValue string

flags   fieldFlags

parents []string

}

Added assignement to default value in func structFieldInfo()

...
if i := strings.Index(tag, " "); i >= 0 {

finfo.xmlns, tag = tag[:i], tag[i+1:]

}
finfo.defaultValue = f.Tag.Get("default")
// Parse flags.
tokens := strings.Split(tag, ",")
... 

encoding/xml/read.go

Added initial assignment to the default value where applicable

in func (p *Decoder) unmarshal(val reflect.Value, start *StartElement) error:

...
for i := range tinfo.fields {

finfo := &tinfo.fields[i]

if finfo.defaultValue != "" {

copyValue(finfo.value(sv), []byte(finfo.defaultValue))

}

switch finfo.flags & fMode {

...