Interfaces: a new leaf in an old book

Using interfaces in Go to write testable code that can be easily modified, or "grows with grace".

Go's interfaces — static, checked at compile time, dynamic when asked for — are, for me, the most exciting part of Go from a language design point of view. If I could export one feature of Go into other languages, it would be interfaces. — Russ Cox

Transcript

1. Interfaces A new leaf in an old book Matthew Cottingham matt@microcosm.cc @mattrco
2. whoami Then: web services, ETLs, messaging. Now: forum software, web services all Go
3. –Russ Cox “Go's interfaces… are, for me, the most exciting part of Go from a language design point of view.”
4. Recap
5. Stringer
6. Implicitly satisfied interfaces • In order to satisfy an interface, we just need to implement the right functions • So it’s easy decouple components even if they’re third party or part of the standard library
7. Decoupling database/sql • sql.DB is a struct type which makes it harder to switch out for a test implementation • Create an interface type (I called it DBer) with same methodset as sql.DB • Replace instances of sql.DB with interface DBer
8. DBer interface type
9. DBer usage
10. Other options • https://github.com/erikstmartin/go-testdb • also, fakedb (internal test package) implements the Driver interface
11. Real-world interfaces • There are some useful examples of interfaces in the standard library: • encoding for text and binary representations • Valuer and Scanner interfaces
12. encoding interface • New in Go 1.2 • Supports Binary and Text Marshal/Unmarshal • Used in e.g. Time and IP types
13. (Un)MarshalText
14. net.IP implementation
15. Valuer and Scanner • Database driver needs to convert Go types to database types and vice-versa
16. PostgreSQL hstore
17. Analysis • go oracle can tell you (among other things)
18. References • http://research.swtch.com/interfaces • http://blog.golang.org/gif-decoder-exercise-in-go- interfaces • http://jmoiron.net/blog/built-in-interfaces/ • Source code modified from: • http://golang.org • https://github.com/lib/pq