Structs in Go (challenge answer)

Warning: Challenge spoiler alert

At the end of the “Structs in Go” article, we asked you to complete the following tasks:

1. Make a new field in our person struct, of type bool, that we’ll use to control whether someone is a friend or not.
2. Use the new field to control which statement is printed out.

If you haven't attempted it; we're about to give you the answer, so now's a good time to go and try it.

The first task is to add a new field in our person struct, that we can use to control whether someone is a friend or not. We’ll call this new field isFriend, to remain consistent.

type person struct {
    name string
    age int
    isFriend bool
}

But we’ve now got a too few values in composite literal error, where we’re using the person struct (below).

me := person{"Simon", 29}

friends := [5]person{
    {"David", 17},
    {"Bill", 42},
    {"Charlie", 12},
    {"Abby", 24},
    {"Edith", 74},
}

This error basically means we’re not passing enough values through; our person struct expects three properties (name, age and isFriend ) but we are only passing through two ( name and age )

Let’s fix this by specifying the isFriend property.

me := person{"Simon", 29, false}

friends := [5]person{
    {"David", 17, true},
    {"Bill", 42, true},
    {"Charlie", 12, true},
    {"Abby", 24, true},
    {"Edith", 74, true},
}

That’s the first task done so lets now update our programme to use the new isFriend field to control which statement is printed out.

We’re already passing the variable, of type person, through to the printAgeBracket function, so we already have access to the isFriend property.

The only change we need to make, in the printAgeBracket function, is to use the new isFriend field (p.isFriend) instead of the isFriend parameter.

func printAgeBracket(p person, isFriend bool) {
    if p.isFriend { // Change this line
        log.Printf("%s: ", p.name)
    } else {
        log.Printf("Hello World. My name is %s.", p.name)
    }

    if p.age < 13 {
        log.Println("I am considered a child")
    } else if p.age < 20 {
        log.Println("I am considered a teenager")
    } else if p.age < 70 {
        log.Println("I am considered an adult")
    } else {
        log.Println("I am considered a pensioner")
    }
}

And now your programme is using the new isFriend field! So, we’re done? Not just yet.

Our programme works fine, but we’ve left our isFriend parameter even though we’re not using it. It’s good practice to clean up unused code; it will help prevent bugs in the future and makes the code look cleaner.

To remove the isFriend parameter from the printAgeBracket function, we just remove it from within the function parenthesis:

func printAgeBracket(p person) {
    if p.isFriend {
        log.Printf("%s: ", p.name)
    } else {
        log.Printf("Hello World. My name is %s.", p.name)
    }

    if p.age < 13 {
        log.Println("I am considered a child")
    } else if p.age < 20 {
        log.Println("I am considered a teenager")
    } else if p.age < 70 {
        log.Println("I am considered an adult")
    } else {
        log.Println("I am considered a pensioner")
    }
}

And then update anything that calls it, to avoid any errors:

printAgeBracket(me)

for i := 0; i < len(friends); i++ {
    printAgeBracket(friends[i])
}

Remember you can always reach out to us with any questions or feedback - we’d love to hear from you!

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