CODEWITHSUNDEEP
go
Marconi
Marconi

Reputation: 3651

In golang, how to embed on custom type?

I have custom types Int64Array, Channel and ChannelList like:

type Int64Array []int64

func (ia *Int64Array) Scan(src interface{}) error {
  rawArray := string(src.([]byte))
  if rawArray == "{}" {
    *ia = []int64{}
  } else {
    matches := pgArrayPat.FindStringSubmatch(rawArray)
    if len(matches) > 1 {
      for _, item := range strings.Split(matches[1], ",") {
        i, _ := strconv.ParseInt(item, 10, 64)
        *ia = append(*ia, i)
      }
    }
  }
  return nil
}

func (ia Int64Array) Value() (driver.Value, error) {
  var items []string
  for _, item := range ia {
    items = append(items, strconv.FormatInt(int64(item), 10))
  }
  return fmt.Sprintf("{%s}", strings.Join(items, ",")), nil
}

type Channel int64

type ChannelList []Channel

How can I embed Int64Array to ChannelList such that I can call Scan and Value methods on it? I tried the following:

type ChannelList []Channel {
    Int64Array
}

but I'm getting syntax error. What's important is to make sure ChannelList items are of type Channel, if this isn't possible via embedding I might just create stand-alone functions to be called by both ChannelList and Int64Array.

Upvotes: 1

Views: 1281

Answers (1)

VonC
VonC

Reputation: 1324937

An anonymous (or embedded field) is found in a struct (see struct type), not in a type alias (or "type declaration").

You cannot embed a type declaration within another type declaration.

Plus, as illustrated by the answers to "Go: using a pointer to array", you shouldn't be using pointers to slice, use directly the slice themselves (passed by value).

Wessie kindly points out in the comments that (ia *Int64Array) Scan() uses pointer to a slice in order to mutate the underlying array referenced by said slice.
I would prefer returning another slice instead of mutating the existing one.
That being said, the Golang Code Review does mention:

If the receiver is a struct, array or slice and any of its elements is a pointer to something that might be mutating, prefer a pointer receiver, as it will make the intention more clear to the reader.

Upvotes: 3

Related Questions