How to create an array of struct arrays of different types?

Question

In my program I got 2 models:

type User struct {
    Name string
}

type Article struct {
    Title string
}

And I got arrays of data of these structs:

users := []User
articles := []Article

I'm trying to iterate over both of them at the same piece of code:

models := [][]interface{} {users, articles}
for _, model := range models {
    log.Printf("%#v", model)
}

But I'm receiving an error:

cannot use users (type []User) as type []interface {} in array element

What am I doing wrong?

This cannot be done. Go is statically typed. Redesign your solution. — Volker, Sep 04 '15 at 12:54
You can't convert any slice to `[]interface{}`. For explanation and solution see [Type converting slices of interfaces in go](http://stackoverflow.com/questions/12753805/type-converting-slices-of-interfaces-in-go). — icza, Sep 04 '15 at 14:27
@WhiteAngel the "go way" is using interfaces, I posted a solution that might help :) — Pablo Fernandez, Sep 04 '15 at 15:31

RoninDev · Answer 1 · 2015-09-04T13:09:26.993

4

You should use []interface{} instead of [][]interface{}
Try it on the go playground

If you want to iterate all structs in your inner arrays, you need to cast them to the proper type and then iterate, like this:

for _, model := range models {
    if u, ok := model.([]User); ok {
        for _, innerUser := range u {
            log.Printf("%#v", innerUser)
        }
    }
    if a, ok := model.([]Article); ok {
        for _, innerArticle := range a {
            log.Printf("%#v", innerArticle)
        }
    }
}

Try it on the go playground

edited Sep 04 '15 at 13:09

answered Sep 04 '15 at 12:58

RoninDev

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1

Thank you for your response. But this is what I was trying to avoid - `switch` statement and checking types. In this case I would have repeating blocks that will do absolutely the same things for each type. So, Go doesn't allow you to do this in a clean way? For me the problem is that I might have 10 different models and even more. – WhiteAngel Sep 04 '15 at 14:15
Maybe you can use interfaces for that? – RoninDev Sep 04 '15 at 17:04
@RoninDev like in my answer? – Pablo Fernandez Sep 04 '15 at 18:38
@PabloFernandez exactly – RoninDev Sep 05 '15 at 08:03

score 1 · Answer 2 · answered Sep 05 '15 at 04:00

1

Maybe I'm not getting your requirements, but what's wrong with just

models := []interface{} {users, articles}
for _, model := range models {
    log.Printf("%#v\n", model)
}

answered Sep 05 '15 at 04:00

newacct

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Pablo Fernandez · Answer 3 · 2015-09-04T15:56:53.720

How about using interfaces to solve your problem? you can even use the default fmt.Stringer interface, used by fmt.Prtinf and other standard methods.

Example:

package main

import "log"
import "fmt"

type User struct {
    Name string
}

type Article struct {
    Title string
}

func (art Article) String() string {
    return art.Title
}

func (user User) String() string {
    return user.Name
}

func main() {
    models := []interface{}{User{"user1"}, User{"user2"}, Article{"article1"}, Article{"article2"}}
    for _, model := range models {
        printable := model.(fmt.Stringer)
        log.Printf("%s\n", printable)
    }
}

Playground: https://play.golang.org/p/W3qakrMfOd

How to create an array of struct arrays of different types?

3 Answers3