Flexible API in Scala

Explains how to write flexible APIs in Scala.

Transcript

1. Flexible API in Scala Jun Tomioka (M3, inc.)
2. M3, Inc. Jun Tomioka Twitter: @jooohn1234 Github: jooohn Love: Our very first baby Had great paternity leave!
3. How do you write your HTTP server interface?
6. http4s
7. http4s • A minimal, idiomatic Scala interface for HTTP • Scala’s answer to Ruby’s Rack • Well designed “typeful” “functional” “streaming” library
8. Let’s see how http4s offers flexible APIs
11. Basically, this is just a Request => F[Response]
12. Request => F[Response]
13. Scala’s functionality / design pattern • Higher kinded type parameters • Type Classes
14. Type parameters • Parameterized type like Java’s Generics
15. Higher kinded type parameters • Type parameters which expect higher kinded types. ◦ F[_] • Generalize “any contextual types” ◦ Option / Future / Try / etc
18. Type Classes • Design pattern for ad-hoc polymorphism • Generalize functionality which can be implemented later.
23. Why type class? • Can extend existing class. • Different implementation for same class. ◦ intAddition / intMultiplication • Independent from an instance. ◦ What if you want `def empty[A]: A` ?
24. Type Classes with higher kinded types • Generalize operations for any contextual value. • Powerful combination!
28. http4s
32. Flexibility of type class • Taking F as type parameter, it allows us to choose which context to use. ◦ http4s basically expects any instance of Effect as F like IO • You can use your own instance of Effect ◦ DB access / API Call / Body parsing ◦ IO seems perfect choice though.
37. Flexible API with Contextual type classes • Declare traits with type parameter F[_] ◦ Never know concrete type ◦ Use type class if any functionality is needed • Offers flexible API with ◦ Higher kinded types ◦ Type classes
38. “Looks too much.” • If you think so, YOU’RE RIGHT. ◦ You may not have to write such APIs BY YOURSELF in your application code. ◦ Instead, USE it for your needs.
39. Thanks!