How do I handle empty values when initializing structs in go?

Question

I'm trying to split a comma separated string and use the values to initalize a struct. This is how I do it right now:

type Address struct {
    Street  string
    City    string
    ZipCode string
}
    
s := strings.Split("street,city,zip", ",")
data := Address{Street: s[0], City: s[1], ZipCode: s[2]}

The problem I'm having is that I have to handle this input as well:

"street,"
"street,city"

Any idea how to do it without going out of range? I've looked into unpacking with triple dots syntax ... but structs does not seem to support it.

@colm.anseo If I have multiple structs and multiple optional fields, its gonna be a lot of checks. Is that normal in Go, no other way around? — Paikz
– Paikz, Commented Apr 5, 2021 at 20:54
It is normal to check the length of a slice when the length is not known at compile time. — user5728991
– user5728991, Commented Apr 5, 2021 at 21:06

user13631587 · Accepted Answer · 2021-04-05 21:40:03Z

3

Check the length of the slice before accessing the element:

data := Address{}
s := strings.Split("street,city,zip", ",")
data.Street = s[0]
if len(s) > 1 {
    data.City = s[1]
}
if len(s) > 2 {
    data.ZipCode = s[2]
}

If this comes up a lot, then write a simple helper function:

func get(s []string, i int) string {
    if i >= len(s) {
        return ""
    }
    return s[i]
}

Use it like this:

data := Address{Street: get(s, 0), City: get(s, 1), ZipCode: get(s, 2)}

answered Apr 5, 2021 at 21:40

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user13631587

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Adrian · Accepted Answer · 2021-04-05 22:12:36Z

1

If you'd rather use slightly more memory and less checks, you could also do:

s := strings.Split("street,city,zip", ",")
s = append(s, make([]string, 3 - len(s))...) // Change 3 to however many fields you expect
data := Address{Street: s[0], City: s[1], ZipCode: s[2]}

What this does is append empty strings to the slice to ensure it always has the right number of elements. Playground example: https://play.golang.org/p/Igj6yT5fffl

answered Apr 5, 2021 at 22:12

Adrian

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