不带名称的函数/方法

Question

I'm really struggling to find a name for a type of function I've come across.

Here is the function in question:

https://github.com/go-fsnotify/fsnotify/blob/master/fsnotify.go#L32

This is how I'm using it (as per the fsnotify example):

        select {

            case event := <-watcher.Events:

                log.Println("Event Triggered: ", event)

In that Println 'event' is returning the formatted string as per the function above, I'm just struggling to understand how a straight call to 'event' is using that function yet I would be expecting it to be accessed like the struct fields (event.Name, event.Op):

event.funcForReturningNicelyFormattedEvent()

It feels like this is a 'default' function as it has no name and it just returns the formatted data - I'm struggling to come up with the name/type/search term so I can find out more and understand the concept and importantly the reasoning behind it better.

Any help is appreciated.

Answer 1

It's very simple - println uses the String() method on any struct that implements it automatically. This is a classic use case of Go's implicit interfaces: every struct that has the methods an interface includes, is considered to be implementing the interface.

If it has func String() string it is considered a Stringer and used by fmt. You can use it on your own structs too, of course.