How to Identify the Last Item in a Go Template Range?

Identifying the Last Item in a Template Range

In Go templates, it can be challenging to identify the last item in a range. The inbuilt $i variable only represents the current index, making it difficult to determine when the iteration is concluding.

To overcome this obstacle, a workaround is to employ a custom function that combines the $i variable with a reflection-based approach to ascertain the length of the data structure being iterated over. By comparing the current index with the length minus one, we can accurately detect the final iteration.

Here's an example of how this custom function can be implemented:

func last(i int, a interface{}) bool {
    return i == reflect.ValueOf(a).Len() - 1
}

By registering this function as part of a FuncMap and using it within a template, you can easily output the desired comma-separated list with "and" appended to the last item.

template.Must(template.New("abc").Funcs(fns).Parse(`{{range $i, $e := .}}{{if $i}}, {{end}}{{if last $i $}}and {{end}}{{$e}}{{end}}.`))

This solution offers a reusable and effective way to identify the last item in a template range, enhancing the flexibility of Go templates for data presentation.

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