Golang: How to append pointer to slice to slice?

Question

I'm a Golang newbie but I thought I had got the essentials of pointers and references straight, but apparently not:

I have a method that must return a []github.Repository , which is a type from the Github client in go.

The API call returns the results paginated so I must cycle until there's no more results, and add the result of each call to the allRepos variable, and return that . Here's what I have so far:

func (s *inmemService) GetWatchedRepos(ctx context.Context, username string) ([]github.Repository, error) {
    s.mtx.RLock()
    defer s.mtx.RUnlock()

    opt := &github.ListOptions{PerPage: 20}

    var allRepos []github.Repository

    for {
        // repos is of type *[]github.Repository
        repos, resp, err := s.ghClient.Activity.ListWatched(ctx, "", opt)

        if err != nil {
            return []github.Repository{}, err
        }

        // ERROR: Cannot use repos (type []*github.Repository) as type github.Repository
        // but dereferencing it doesn't work, either
        allRepos = append(allRepos, repos...)
        if resp.NextPage == 0 {
            break
        }
        opt.Page = resp.NextPage
    }

    return allRepos, nil

}

My question: how can I append the results of each call and return a result of type []github.Repository ?

Also, why doesn't dereferencing work here? I've tried replacing allRepos = append(allRepos, repos...) with allRepos = append(allRepos, *(repos)...) but I get this error message:

Invalid indirect of (repos) (type []*github.Repository)

Answer 1

Well, something is not okay here:

You say in the comment that "repos is of type *[]github.Repository " but the compiler's error message indicates that repos is of type []*Repository ". The compiler is never (except when buggy) wrong.

Note that *[]github.Repository and []*Repository are completely different types, especially the second is not a slice of Repositories and you cannot (really, there is no way ) dereference these pointers during append() : You have to write a loop and dereference each slice item and append one by one.

What is strange too: github.Repository and Repository seem to be two different types one from package github, the other from the current package. Again, you'll have to get that straight too.

Note that there are no references in Go. Stop thinking about these immediately: This is a concept from other languages which is not helpful (as inexistent) in Go.

Answer 2

In your example the dereferencing is not correct. You should make it like this:

allRepos = append(allRepos, *repos...)

Here a simple example with dereferencing a pointer to a slice of string. https://play.golang.org/p/UDzaG5z8Pf