Go Interface/Container usage - interface

Question

Newbie Go programmer here. I'm writing a package that reads a JSON configuration file. It uses the built-in JSON decoding, of course. But I want it to be able to include other JSON files as well, by looking for an array of filenames with the key of 'Includes'. I got it working as just a function and passing in a struct for the JSON data that includes a slice of strings labeled 'Includes', but I don't know how to specify this as a package.
Here's the function:
func ReadConfig(filename string, configuration *Configuration) error {
log.Println("reading file", filename)
file, err := os.Open(filename)
if err != nil {
log.Println("Can't read", filename)
return err
}
decoder := json.NewDecoder(file)
if err := decoder.Decode(&configuration); err != nil {
log.Println(err)
return err
}
includes := make([]string, len(configuration.Includes))
copy(includes, configuration.Includes)
config.Includes = configuration.Includes[0:0]
for _, inc := range includes {
log.Println(inc)
if err := ReadConfig(inc, configuration); err != nil {
return err
}
}
return nil
}
Which works with:
type Configuration struct {
Includes []string
.... other defs
}
But, in a package, I want ReadConfig to take any kind Configuration struct, as long as one of its members is 'Includes []string'.
I believe I need to change the ReadConfig def to:
func ReadConfig(filename string, configuration interface{})
But what I don't know is how to access the Includes slice within that.

Answer 1

Just create an interface for it
type Configurable interface {
Configuration() []string
}
And then provide a Configuration method instead of a field for your structs, and change the signature of your function to func ReadConfig(filename string, configuration Configurable).
It'd be much easier to just pass in the slice instead of the struct though.