How to get the reflect.Type of an interface?

Question

In order to determine whether a given type implements an interface using the reflect package, you need to pass a reflect.Type to reflect.Type.Implements(). How do you get one of those types?

As an example, trying to get the type of an uninitialized error (interface) type does not work (it panics when you to call Kind() on it)

var err error fmt.Printf("%#v\n", reflect.TypeOf(err).Kind()) 

Answer 1

Do it like this:

var err error t := reflect.TypeOf(&err).Elem() 

Or in one line:

t := reflect.TypeOf((*error)(nil)).Elem() 

Answer 2

Even Shaws response is correct, but brief. Some more details from the reflect.TypeOf method documentation:

// As interface types are only used for static typing, a common idiom to find // the reflection Type for an interface type Foo is to use a *Foo value.  writerType := reflect.TypeOf((*io.Writer)(nil)).Elem()  fileType := reflect.TypeOf((*os.File)(nil)).Elem() fmt.Println(fileType.Implements(writerType))