How to Extract Template Field Names from a Parsed Go Template?
Dec 18, 2024 pm 09:43 PMRetrieving a List of Template Actions from a Parsed Template
How can you extract the templates defined in a template as a slice of strings? Consider a template like:
<h1>{{ .name }} {{ .age }}</h1>
You wish to obtain []string{"name", "age"}.
Inspecting the Parsed Template Tree
The parsed template is represented by a template.Tree containing details about the template structure. Each node of this tree has a Node.Type() method that provides information about its type. Relevant types include:
- NodeAction: Non-control actions such as field evaluations
- NodeField: Field or method names
Iterating the Tree
To identify actions within the template, you can iterate through the tree and explore the nodes. The following sample function demonstrates this process:
import ( "text/template/parse" ) func ListTemplFields(t *template.Template) []string { return listNodeFields(t.Tree.Root, nil) } func listNodeFields(node parse.Node, res []string) []string { if node.Type() == parse.NodeAction { res = append(res, node.String()) } if ln, ok := node.(*parse.ListNode); ok { for _, n := range ln.Nodes { res = listNodeFields(n, res) } } return res }
Example Usage
To determine the fields required for the template:
t := template.Must(template.New("cooltemplate"). Parse(`<h1>{{ .name }} {{ .age }}</h1>`)) fmt.Println(ListTemplFields(t))
The output will be:
[{{.name}} {{.age}}]
Note: This demonstration is not comprehensive and may not handle all cases. However, it illustrates the concept of extracting template actions by introspecting the parsed template tree.
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