Assign value to field in struct if empty [duplicate]

Question

I have a struct defined

type data struct {
  invitecode string
  fname string
  lname string
}

which I populate from retrieving form data after parsing

...

r.ParseForm()

new user := &data{
  invitecode: r.FormValue("invitecode"),
  fname: r.FormValue("fname")
  lname: r.FormValue("lname")
}

I did like to check if the invitecode field obtained from the form is empty and if so, populate it by calling a function but if it is not, to populate it with the retrieved value (invitecode: if newUser.invitecode == "" {"Mr"} else {lnames.title},). I understand go doesn't have a tenary operator which I thought of using and reading the questions here, here, here & here implies using an if else statement but I can't seem to get it to work. Preferable, I am looking for a solution that check's while assigning a new variable. Trying the code below doesn't seem to work. Any help would be appreciated.

package main

import (
    "fmt"
)

type data struct {
    invitecode string
    fname      string
    lname      string
}

func main() {
    var user data

    newUser := map[string]string{"invitecode": "", "fname": "Dude", "lname": "Did"}
    user = &data{
        invitecode: if newUser.invitecode == "" {"Mr"} else {lnames.title},
        fname:      newUser.fname,
        lname:      newUser.lname,
    }
    fmt.Println(user)
}

Are you having some issue using an if statement? There is nothing in your quoted code that attempts to do what you're describing. — Adrian
– Adrian, Commented Nov 20, 2017 at 17:02

maerics · Accepted Answer · 2017-11-20 17:16:59Z

4

You cannot use an if ... else statement inline like you would a ternary operator (or if/else statements) in other languages, you must simply do it procedurally:

user := &data{ /* ... */ }

if user.invitecode == "" {
  user.invitecode = "Mr"
} else {
  user.invitecode = lnames.title
}

answered Nov 20, 2017 at 17:16

maerics

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2 Comments

maerics Over a year ago

Yup, seems like go was designed for explicit clarity, not for conciseness.

Kaedys Over a year ago

No "seems" about it, Go was explicitly designed in that manner. The developers of the language state it several times in their various blogs about Go error handling. Their view is very specifically and openly that clarity > conciseness.

Adrian · Accepted Answer · 2022-11-08 14:26:57Z

3

Go does not have ternaries, nor can you do an inline if like you've shown in the code. You will have to do a normal if block:

user = &data{}
if newUser.inviteCode == "" {
    user.invitecode = "Mr"
} else {
    user.invitecode = lnames.title
}

And so on. You could extract this into a function:

func coalesce(args ...string) string {
    for _,str := range args {
        if str != "" {
            return str
        }
    }
    return ""
}

And use it like so:

user.invitecode = coalesce(lnames.title, "Mr")

Of course, if you deal with multiple types (not just strings), you'll need one such function for each type.

edited Nov 8, 2022 at 14:26

answered Nov 20, 2017 at 17:17

Adrian

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2 Comments

driftavalii Over a year ago

Thanks, was trying to assign all the fields in one go, can the other fields be assigned in the else block and is that a proper way to do it?

Adrian Over a year ago

Sure, if that's the behavior your'e looking for.

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