How to Access URL Parameters Within a Template Range Loop in Go?

Accessing URL Parameters Within a Template Range Loop

When working with Go templates, it's essential to understand how data is accessible within loops. Consider the following code and template:

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

func main() {
    users := []User{
        {Username: "Alice", Email: "alice@example.com"},
        {Username: "Bob", Email: "bob@example.com"},
    }

    renderer.HTML(w, http.StatusOK, "users/index", map[string]interface{}{
        "lang":  chi.URLParam(r, "lang"),
        "users": users,
    })
}

{{ range .users }}
  

{{ end }}

In this scenario, you may encounter an error indicating that the "lang" field is not part of the "User" struct. To address this, we can leverage the concept of "dot" and the special variable "$."

Understanding Dot and $

When a loop is invoked, the contents of "dot" (.) are assigned to the special variable "$." This allows us to access data from outside the loop within the range block. For instance, to access the "lang" parameter, we can use "$" as follows:

{{ range .users }}
  

{{ end }}

This approach successfully resolves the issue, enabling you to access the "lang" parameter within the range loop. The behavior of "dot" and "$" is documented in the Go templating guide.

Alternative Approaches

If you encounter scenarios where accessing data using "$" is challenging due to nested loops, consider alternative options such as assigning "dot" to a temporary variable or using the "with" statement to create a dedicated scope for assigning data.

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