Convert []interface to []string in Golang

Question

I'm using the github.com/fatih/structs package to convert values of all fields of a struct into []interface{} with the toValues() function. See here. This works fine, but eventually I want to write the values to a csv file by using the csv package. The csv.Write() function requires []string as input.

So in short: how can I easily convert the output of toValues() into an array of strings?

Solution

You can't simply convert []interface{} to []string even if all the values are of concrete type string, because those 2 types have different memory layout / representation. For details see Cannot convert []string to []interface {}.

You have to define how you want values of different types to be represented by string values.

The easiest and sensible way would be to iterate over the values, and use fmt.Sprint() to obtain a string representation of each, e.g.:

t := []interface{}{
    "zero",
    1, 2.0, 3.14,
    []int{4, 5},
    struct{ X, Y int }{6, 7},
}
fmt.Println(t)

s := make([]string, len(t))
for i, v := range t {
    s[i] = fmt.Sprint(v)
}
fmt.Println(s)
fmt.Printf("%q\n", s)

Output (try it on the Go Playground):

[zero 1 2 3.14 [4 5] {6 7}]
[zero 1 2 3.14 [4 5] {6 7}]
["zero" "1" "2" "3.14" "[4 5]" "{6 7}"]

Comments

[Rogier Lommers]

Thanks; didn't thought about using fmt.Sprint. Working fine now!

[Alireza Soori]

wow, this helped me so much... but still I hope for a more robust way with assertion

[Eric Lindsey]

@AlirezaSoori you can have this with type assertion: just change fmt.Sprint(v) with v.(string).

[Lou]

@icza - This is weird - I've tried using this answer for a similar problem, but I simply can't access the []interface{} when iterating, it returns a "cannot range over foobar (type interface{})" error. If you have time I'd greatly appreciate your input - stackoverflow.com/questions/70611033/…