How to Correctly Pass Functions to Golang Templates and Avoid 'Function Not Defined' Errors?

Addressing Errors When Passing Functions to Golang Templates

When working with Golang templates, passing custom functions can sometimes lead to errors, such as the "function not defined" error. Here's how to resolve this issue and implement function passing correctly.

To begin, ensure that custom functions are registered before parsing the templates. Parsing registries functions, allowing the parser to recognize them and distinguish them from valid identifiers. Utilize the template.New() function to create a new, undefined template and call the Template.ParseFiles() method to parse the template files. For example:

t, err := template.New("struct.tpl").Funcs(template.FuncMap{
    "makeGoName": makeGoName,
    "makeDBName": makeDBName,
}).ParseFiles("templates/struct.tpl")

Additionally, note that the template.New() function requires the basename of the executed file.

Furthermore, it's crucial to handle the error returned by Template.Execute(). Add an if statement to handle any errors that may arise while executing the template:

if err := t.Execute(os.Stdout, data); err != nil {
    fmt.Println(err)
}

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