How do I differentiate a missing value from 0 in a map with Go's text/template?

Question

In Go I have a map[string]int. I want to display values from this map through a Template from the text/template package. If the map doesn't contain a specific value, I want to display "n/a" instead. This is what I have tried:

{{with index $.MyMap .MyKey}}{{.}}{{else}}n/a{{end}}

Unfortunately this doesn't work if the map contains a value for my key, but the value is 0. Then "n/a" is also displayed. How can I make sure that "n/a" is only displayed, if the map didn't contain the requested value?

Answer 1

You can create a template function, which returns n/a if key does not exist.

funcMap := template.FuncMap{
    "GetValue": func(m map[string]int, key string) string {
        if value, ok := m[key]; ok {
            return fmt.Sprintf("%d", value)
        }
        return "n/a"
    },
}

In you template you can call GetValue function. For example -

 tmpl := `{{- $key1 := "one" -}}
            {{- $key2 := "four" -}}
            Value for '{{ $key1 }}': {{ GetValue . $key1 }} \n
            Value for '{{ $key2 }}': {{ GetValue . $key2 }}`

Output is

Value for 'one': 1 /n
Value for 'four': n/a