How to Access External Parameters in a Go Template Range Loop?

Go Template Accessing External Parameter in a Range Loop

Consider a situation where you have a User struct with fields like Username, Password, and Email. In a web application, the URL structure may include a language parameter (en) that needs to be accessed within a template that iterates over users.

In the provided template:

{{ range .users }}
  <form action="/{{ .lang }}/users" method="POST">
    <input type="text" name="Username" value="{{ .Username }}">
    <input type="text" name="Email" value="{{ .Email }}">
  </form>
{{ end }}

Accessing .lang within the range loop results in the following error:

"can't evaluate field X in type Y (X not part of Y but stuck in a {{range}} loop)"

To solve this issue, it's necessary to access the .lang parameter from outside the loop. This can be achieved by using the $ variable. After the range invocation, the contents of the range variable (. in this case) are assigned to $. Therefore, the template can be modified as follows:

{{ range .users }}
  <form action="/{{ $.lang }}/users" method="POST">
    <input type="text" name="Username" value="{{ .Username }}">
    <input type="text" name="Email" value="{{ .Email }}">
  </form>
{{ end }}

By using $, the template can successfully access the .lang parameter despite it not being a field in the User struct.

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