How to call a function on a custom type

Question

I've seen some similar questions but I can't find one that solves my problem.

I have a custom Money type that aliases int64 with a function that formats the value as a string:

type Money int64

func (m *Money) Format() string {
    abs := math.Abs(int64(*m))

    dollars := int64(abs) / 100
    cents := int64(abs) % 100

    sign := ""
    if *m < 0 {
        sign = "-"
    }

    return fmt.Sprintf("%s$%d.%0.2d", sign, dollars, cents)
}

I have a HTML template that I pass a data struct. The struct has a list of invoice items on it that each have a Money field, and another Money field that holds the total.

type InvoiceItem {
    // ...
    Cost money.Money
}

type data struct {
    Name      string
    Items     []*model.InvoiceItem
    StartDate time.Time
    EndDate   time.Time
    Total     money.Money
}

I pass the data to my template and execute it:

t := template.Must(template.New(title).Parse(templateString))
t.Execute(&buf, data)

In my template I range over the invoice items and call the Format function on the Money object. This works:

{{range .Items}}
<tr>
    <td>{{.Description}}</td>
    <td>{{.Cost.Format}}</td>
</tr>
{{end}}

Later on I attempt to print the total field:

<td><strong>{{ .Total.Format }}</strong></td>

My templates throws an error:

 ... executing "Invoice Items" at <.Total.Format>: can't evaluate field Format in type money.Money

Why is it that I can call Format on the Money field when I range over the list of invoice items, but I can't call it on the data.Total object? From the error message it seems that the template knows that the type of Total is Money, so what's the problem?

Thanks @Volker, that was the problem. If you want to put this in an answer I'll accept it. — Matt, Dec 05 '18 at 23:32

score -1 · Answer 1 · answered Dec 05 '18 at 09:36

-1

It looks like your data struct is unexported. Do this:

type Data struct { 

}

answered Dec 05 '18 at 09:36

Himanshu Patel

103
10

It doesn't need to be exported as long as its fields/methods are (and they are). – Adrian Dec 05 '18 at 14:50
The struct is local to the method it's used in, and I can already access the fields in the template. – Matt Dec 05 '18 at 21:52

How to call a function on a custom type

1 Answers1