Initialize structs from list of strings

Question

I'm trying to initialize structs from a list of strings, but the compiler is throwing the following error. I'm still learning the language so excuse my ignorance, but is this solved by utilizing type assertion?

ERROR: v.UberX undefined (type string has no field method UberX)

type Galaxy struct {
    UberX     int64
    UberY     int64
}

func main() {
    galaxies := []string{"andromeda", "milkyway", "maffei"}
    for _, v := range galaxies {
        v := &Galaxy{}
    }
    for _, v := range galaxies {
        v.UberX += 1000
        v.UberY += 750
    }
}

icza · Accepted Answer · 2016-11-15 10:58:25Z

2

Your Galaxy struct doesn't even store the name, in your attempt there isn't any connection between the names and the struct values. Add the name to the struct:

type Galaxy struct {
    Name  string
    UberX int64
    UberY int64
}

Next, in your first loop you create a *Galaxy value, but you only store it in a local variable v which by the way shadows the loop variable v:

for _, v := range galaxies {
    v := &Galaxy{}
}

You need a slice of Galaxy or a slice of *Galaxy which you can populate:

gs := make([]*Galaxy, len(galaxies))

Then 1 loop is enough to loop over the galaxy names and populate the gs slice:

for i, v := range galaxies {
    gs[i] = &Galaxy{
        Name:  v,
        UberX: 1000,
        UberY: 750,
    }
}

Verifying the result:

for _, v := range gs {
    fmt.Printf("%+v\n", v)
}

Output (try it on the Go Playground):

&{Name:andromeda UberX:1000 UberY:750}
&{Name:milkyway UberX:1000 UberY:750}
&{Name:maffei UberX:1000 UberY:750}

Recommended to go through the Golang Tour first to learn the basics.

answered Nov 15, 2016 at 10:58

icza

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1 Comment

Alex Demskie Over a year ago

No doubt I've got lots of reading to do. Was hoping I could practice some of it in the meantime. My thought process was that the "name" field would be unnecessary if I could initialize the struct with the proper name. Thanks

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