Learning Functional Programming in Go

Design with Duck Typing

As mentioned in the previous chapter, this is known as Duck Typing. It's a powerful design pattern. A thing is defined not by its type hierarchy but by its behaviors.

Here's an example of a File interface from the github.com/couchbase/moss package:

// The File interface is implemented by os.File. App specific// implementations may add concurrency, caching, stats, fuzzing, etc.type File interface {       io.ReaderAt       io.WriterAt       io.Closer       Stat() (os.FileInfo, error)       Sync() error       Truncate(size int64) error}

Here's another example of it from Go's mime/multipart project:

// File is an interface to access the file part of a multipart message.// Its contents may be either stored in memory or on disk.type File interface { io.Reader ...