What are interfaces and how do they differ from classes?

In Go, an interface is a set of methods that a type must implement to be considered as conforming to that interface. Unlike classes, interfaces do not contain implementations, only describing behavior.

Key differences:

• Interfaces describe only methods, while classes (in Go — structs) contain data and methods.
• In Go, there are no classes as such, only structs and interfaces.
• A type automatically implements an interface if it has all the methods of the interface (implicit implementation).

Example:

// Interface
 type Reader interface {
     Read(p []byte) (n int, err error)
 }

// Struct implementing the interface
 type File struct {}

 func (f File) Read(p []byte) (n int, err error) {
     // implementation
     return 0, nil
 }

 func main() {
     var r Reader = File{} // File implements Reader
 }