如何从函数返回slice的更改值？

Question

I'm new to go so forgive me if this is a trivial question. I want to iterate over a slice of posts and increment the value of Views of each post:

    func incrementViews(posts []model.Post) []model.Post {
        for _, v := range posts { 
            v.Views++
            fmt.Println(v.Views) //Views incremented by 1
        }
        return posts
    }

    incrementViews(posts) //Views not changed

The printed values are changed but when I call incrementViews(posts) the returned values are unchanged.

I tried to solve this by using * of & but could not manage to do so perhaps because I come from Python background and have lose grasp of moving around variables by pointers and values.

Answer 1

The code in the question is updating the local variable v. Either change the slice to *model.Post or update the value in the slice using the index operator. The former requires changes to the caller.

func incrementViews(posts []*model.Post) []*model.Post {
    for _, v := range posts { 
        v.Views++
    }
    return posts
}

func incrementViews(posts []model.Post) []model.Post {
    for i := range posts { 
        posts[i].Views++
    }
    return posts
}

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EDIT:

Both approaches works, see here: https://play.golang.org/p/90BNOFYaKL