Question

I’m writing a Google App Engine Go application. In it, I want to handle some calls separately in different .go files. Should I call “init()” function separately in each of those files, or just declare it in one file and call some other functions for initialisation of each .go file?

For example, if I’d have two files, user.go:

package User

import(
    "http"
    "fmt"
)

func init() {
    http.HandleFunc("/", hello)
}

func hello(w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Hello, user!")
}

And admin.go:

package Admin

import(
    "http"
    "fmt"
)

func init() {
    http.HandleFunc("/admin/", hello)
}

func hello(w http.ResponseWriter, r *http.Request) {
    fmt.Fprint(w, "Hello, admin!")
}

Is such an initialisation correct, or is it advised against something like this?

Answer 1

According to Go language specification:

• all initialization code is run in a single goroutine, and

• init() functions within a single package execute in unspecified order

In your case, the packages User and Admin are independent (User does not import Admin, nor Admin imports User). This means that:

• the two init() functions in User and Admin execute in unspecified order

---

Joining the bodies of the two init() functions in a single init() function would look like this:

func init() {
    http.HandleFunc("/", User.Hello)
    http.HandleFunc("/admin/", Admin.Hello)
}

Notice that it is irrelevant whether the program first registers "/" or "/admin/". So, the following code is also valid :

func init() {
    http.HandleFunc("/admin/", Admin.Hello)
    http.HandleFunc("/", User.Hello)
}

From the above two snippets of code, we can see that it is OK for http.HandleFunc("/", ...) and http.HandleFunc("/admin/", ...) to be called in unspecified order.

---

Because "/" and "/admin/" can be registered in any order, and all init() functions run in a single goroutine, the answer to your question is: Yes, such an initialisation correct.