How to Access Non-Struct Fields in Go Template Range Loops?

Go Template Error: Accessing Non-Struct Field in Range Loop

In Go HTML templates, accessing fields that are not part of the iterated struct in a range loop can cause the "can't evaluate field X in type Y" error.

To solve this issue, let's examine a scenario where a User struct lacks the .lang field but the template needs to access it.

Sample User Struct:

type User struct {
    Username string
    Password []byte
    Email string
    ...
}

URL Structure:

example.com/en/users

Template Code:

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

Error:

"can't evaluate field lang in type User"

Solution:

To access .lang from within the loop, you can use the $ variable, which is assigned the value of dot (.) after execution of range.

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

This is because according to the Go template documentation, "$ is set to the data argument passed to Execute, that is, to the starting value of dot."

Therefore, the $ variable can be used to access fields that are not part of the struct being iterated over within a range loop.

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