Flexible API in Scala - Speaker Deck

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Flexible API in Scala Jun Tomioka (M3, inc.)

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M3, Inc. Jun Tomioka Twitter: @jooohn1234 Github: jooohn Love: Our very first baby Had great paternity leave!

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How do you write your HTTP server interface?

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http4s

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http4s ● A minimal, idiomatic Scala interface for HTTP ● Scala’s answer to Ruby’s Rack ● Well designed “typeful” “functional” “streaming” library

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Let’s see how http4s offers flexible APIs

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Basically, this is just a Request => F[Response]

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Request => F[Response]

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Scala’s functionality / design pattern ● Higher kinded type parameters ● Type Classes

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Type parameters ● Parameterized type like Java’s Generics

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Higher kinded type parameters ● Type parameters which expect higher kinded types. ○ F[_] ● Generalize “any contextual types” ○ Option / Future / Try / etc

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Type Classes ● Design pattern for ad-hoc polymorphism ● Generalize functionality which can be implemented later.

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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` ?

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Type Classes with higher kinded types ● Generalize operations for any contextual value. ● Powerful combination!

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http4s

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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.

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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

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“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.

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Thanks!