How to Unmarshal XML Elements with Attributes and Floating-Point Values in Golang?

Understanding XML Element Unmarshaling in Golang

Unmarshaling XML elements into Go structs can be straightforward, but certain aspects may require clarification. This article addresses the specifics of unmarshaling XML elements with attributes and floating-point values.

Structs and Unmarshaling

To unmarshal XML, you need to define a corresponding Go struct. The attributes and values in the XML element map to fields in the struct. For example, the following code defines a struct ThingElem that represents a <thing> XML element:

<code class="go">type ThingElem struct {
    Prop  int   `xml:"prop,attr"`
    Value float // ???
}</code>

However, since the XML element contains a floating-point value, the Value field is currently missing its type.

Using Value to Unmarshal Floating-Point Values

To unmarshal the floating-point value, you can use the Value annotation. This tells the unmarshaler to map the text within the <thing> tags to the Value field:

<code class="go">type ThingElem struct {
    Prop  int     `xml:"prop,attr"`
    Value float64 // Use float64 for float value
}</code>

XMLName and Unmarshaling

The XMLName field is used to specify the XML element name associated with the struct. Generally, you only need to use XMLName when there is ambiguity in determining which element should map to a struct. In this case, there is no ambiguity, so using XMLName is not necessary.

Wrapping the Struct

If you prefer, you can wrap the ThingElem struct in another struct to handle the root element:

<code class="go">type ThingWrapper struct {
    T ThingElem `xml:"thing"`
}</code>

This wrapper provides a way to group the ThingElem struct elements for convenience.

Sample XML

To illustrate the unmarshaling process, here is an example of the XML you provided:

<code class="xml">&lt;thing prop=&quot;1&quot;&gt;
  1.23
&lt;/thing&gt;
&lt;thing prop=&quot;2&quot;&gt;
  4.56
&lt;/thing&gt;</code>

By using the ThingElem struct and following the guidelines above, you should be able to successfully unmarshal this XML into Go structures.

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