How to print the slice of pointers to get the values instead of their address without iteration at go?

Question

This kind output required for debugging purpose. To get actual value of slice of pointers, every time a iteration is getting required.

Is there any way, we can directly have the value instead of the address of each item present at slice using simple fmt.printf()?

Here is a code snippet : https://play.golang.org/p/bQ5vWTlKZmV

package main

import (
    "fmt"
)

type user struct {
    userID int
    name   string
    email  string
}

func main() {
    var users []*user
    addUsers(users)
}

func addUsers(users []*user) {
    users = append(users, &user{userID: 1, name: "cooluser1", email: "[email protected]"})
    users = append(users, &user{userID: 2, name: "cooluser2", email: "[email protected]"})
    printUsers(users)
    printEachUser(users)

}

func printUsers(users []*user) {
    fmt.Printf("users at slice %v \n", users)
}

func printEachUser(users []*user) {
    for index, u := range users {
        fmt.Printf("user at user[%d] is : %v \n", index, *u)
    }
}

At above code, if I am printing the slice directly by fmt.printf , I get only the address of the values instead of actual value itself.

output : users at slice [0x442260 0x442280]

To read to the values always, i have to call func like printEachUser to iterate the slice and get the appropriate value .

output: user at user[0] is : {1 cooluser1 [email protected]} user at user[1] is : {2 cooluser2 [email protected]}

Is there any way, we can read the values inside the slice of pointers using fmt.printf and get value directly like below ?

users at slice [&{1 cooluser1 [email protected]} , &{2 cooluser2 [email protected]}]

Answer 1

This kind output required for debugging purpose.

Is there any way, we can read the values inside the slice of pointers using fmt.Printf and get value directly like below ?

users []*user
fmt.Printf("users at slice %v \n", users)

users at slice [&{1 cooluser1 [email protected]}, &{2 cooluser2 [email protected]}]

---

Package fmt

import "fmt"

type Stringer

Stringer is implemented by any value that has a String method, which defines the “native” format for that value. The String method is used to print values passed as an operand to any format that accepts a string or to an unformatted printer such as Print.

type Stringer interface {
        String() string
}

---

For example,

package main

import (
    "fmt"
)

type user struct {
    userID int
    name   string
    email  string
}

type users []*user

func (users users) String() string {
    s := "["
    for i, user := range users {
        if i > 0 {
            s += ", "
        }
        s += fmt.Sprintf("%v", user)
    }
    return s + "]"
}

func addUsers(users users) {
    users = append(users, &user{userID: 1, name: "cooluser1", email: "[email protected]"})
    users = append(users, &user{userID: 2, name: "cooluser2", email: "[email protected]"})

    fmt.Printf("users at slice %v \n", users)
}

func main() {
    var users users
    addUsers(users)
}

Playground: https://play.golang.org/p/vDmdiKQOpqD

Output:

users at slice [&{1 cooluser1 [email protected]}, &{2 cooluser2 [email protected]}] 

Answer 2

You can use spew

go get -u github.com/davecgh/go-spew/spew

func spewDump(users []*user) {
    _, err := spew.Printf("%v", users)
    if err != nil {
        fmt.Println("error while spew print", err)
    }
}

Output:

[<*>{1 cooluser1 [email protected]} <*>{2 cooluser2 [email protected]}]