Taking Kotlin to production, Seriously

Haim Yadid / Next Insurance
mapOf(
taking?. kotlin to production
)
Seriously!!

Disclaimer
‫בה‬ ‫לנאמר‬ ‫לייחס‬ ‫ואין‬ ‫סאטירה‬ ‫תוכנית‬ ‫הינה‬ ‫זו‬ ‫תוכנית‬
‫כלשהי‬ ‫תכנות‬ ‫בשפת‬ ‫לפגוע‬ ‫ניסיון‬ ‫או‬ ‫אחרת‬ ‫משמעות‬ ‫שום‬
‫בה‬ ‫המופיעים‬ ‫מהתכנים‬ ‫נפגע‬ ‫חש‬ ‫הנך‬ ‫זאת‬ ‫בכל‬ ‫אם‬
‫מראש‬ ‫מתנצלים‬ ‫אנו‬ ‫בסקאלה‬ ‫מתכנת‬ ‫אתה‬ ‫אם‬ ‫או‬

About Me
❖ Developing software since 1984 (Boy, am I getting old?)
❖ Basic -> Pascal -> C -> C++ -> Java -> Kotlin
❖ Architect in Mercury
❖ Independent performance expert for 7 years
❖ Backend developer in

❖ Founded in the Beginning of 2016
❖ HQ@Palo Alto RnD@Kfar Saba
❖ Aims to disrupt the Small businesses insurance ﬁeld
❖ Providing online experience which is simple fast and
transparent
❖ We started to write real code on May 2016

Kotlin
Java
Javascript
Node.JS
Dropwizard
RDS (mysql)

What is Kotlin ?
❖ Statically typed programming language
❖ for the JVM, Android and the browser (JS)
❖ 100% interoperable with Java™ (well almost)
❖ Developed by Jetbrains
❖ Revealed as an open source in July 2011
❖ v1.0 Release on Feb 2016
❖ 1.0.5 current stable version (28.11.2016)

Kotlin Features
❖ Concise
❖ Safe
❖ Versatile
❖ Practical
❖ Interoperable

Why Kotlin
Java Scala Cloju
Groovy/
JRuby
Java8
Strongly 
Typed
Loosely 
Typed
OO/verbose Functional/Rich
)))))))))))))))))))))))))))))))

Why Kotlin
Java Scala Cloju
Groovy/
JRuby
Java8
Strongly 
Typed
Loosely 
Typed
OO/verbose Functional/Rich
Kotlin )))))))))))))))))))))))))))))))

Scala can do it !! ?
❖ Yes Scala can do it
❖ Academic / Complicated
❖ Scala compile time is horriﬁc
❖ Operator overloading -> OMG

Getting Started
❖ Kotlin has very lightweight standard library
❖ Mostly rely on Java collections for good (interop) and for
bad (all the rest)
❖ Kotlin compiles to Java6 byte code
❖ Has no special build tool just use Maven / Gradle

Kotlin & Android
❖ Kotlin got widely accepted on the android community
❖ Runtime has low footprint
❖ Compiles to …. Java 6
❖ Brings lambdas to Android dev and a lot of cool features

Trivial Stuff
❖ No new keyword
❖ No checked exceptions
❖ == structural equality
❖ === referencial equality
❖ No primitives (only under the hood)
❖ No arrays they are classes
❖ Any ~ java.lang.Object

Fun
❖ Functions are denoted with the fun keyword
❖ They can be member of a class
❖ Or top level functions inside a kotlin ﬁle
❖ can support tail recursion
❖ can be inlined
❖ fun funny(funnier: String) = "Hello world"

Fun Parameters
❖ Pascal notation
❖ Function parameters may have default values
❖ Call to function can be done using parameter names
fun mergeUser(first: String = "a", last: String) = first + last 
 
fun foo() { 
mergeUser(first="Albert",last= "Einstein") 
mergeUser(last= "Einstein") 
}

Extension functions
❖ Not like ruby monkey patching
❖ Only extend functionality cannot override
❖ Not part of the class
❖ Static methods with the receiver as ﬁrst a parameter
fun String.double(sep: String) = "$this$sep$this"

❖ variables are declared using the keywords
❖ val (immutable)
❖ var (mutable)
❖
fun funny(funnier: String): String { 
val x = "Hello world" 
return x 
}
val /var

Classes
❖ less verbose than Java
❖ no static members (use companion object)
❖ public is default
❖ Must be declared open to be overridden
❖ override keyword is mandatory
class Producer(val name:String, val value: Int)

Properties
❖ All members of classes are access via proper accessors
(getter and setters)
❖ The usage of getters and setters is implicit
❖ one can override implementation of setters and getters

Delegate Class
interface Foo { 
fun funfun() 
} 
 
class FooImpl(val x: Int) : Foo { 
override fun funfun() = print(x) 
} 
 
class Wrapper(f: Foo) : Foo by f 
 
fun main(args: Array<String>) { 
val f = FooImpl(10) 
val wf = Wrapper(f) 
wf.funfun() // prints 10 
}

Smart Casts
❖ If you check that a class is of a certain type no need to
cast it
open class A { 
fun smile() { println(":)")} 
} 
 
class B : A() { 
fun laugh() = println("ha ha ha") 
} 
 
fun funnier(a: A) { 
if (a is B ) { 
a.laugh() 
} 
}

Null Safety
❖ Nullability part of the type of an object
❖ Option[T] Optional<T>
❖ Swift anyone ?
var msg : String = "Welcome" 
msg = null
val nullableMsg : String? = null

Safe operator ?.
❖ The safe accessor operator ?. will result null
❖ Elvis operator for default
fun funny(funnier: String?): Int? { 
 
println(x?.length ?: "") 
return x?.length 
}

Bang Bang !!
❖ The bang bang !! throws an NPE if object is null
fun funny(funnier: String?): String { 
return funnier!! 
}

Data classes
❖ Less powerful version of to case classes in Scala
❖ Implementation of
❖ hashcode() equals()
❖ copy()
❖ de structuring (component1 component2 …)
data class User(val firstName: String, val lastName:
String) 
 
fun smile(user: User) { 
val (first,last) = user 
}

When
❖ Reminds Scala’s pattern matching but not as strong
❖ More capable than select in java
when (x) { 
is Int -> print(x + 1) 
is String -> print(x.length + 1) 
is IntArray -> print(x.sum()) 
}

Sane Operator Overloading
❖ override only a set of the predeﬁned operators
❖ By implementing the method with the correct name
Expression Translated to
a + b a.plus(b)
a - b a.minus(b)
a * b a.times(b)
a / b a.div(b)
a % b a.mod(b)
a..b a.rangeTo(b)

Sane Operator Overloading
data class Complex(val x: Double, val y: Double) { 
operator fun inc(): Complex { 
return Complex(x + 1, y + 1) 
} 
 
infix operator fun plus(c: Complex): Complex { 
return (Complex(c.x + x, c.y + y)) 
} 
 
}

Collections
❖ no language operators for construction of lists and maps
❖ using underlying java collections
❖ Have two versions mutable and immutable
❖ Immutability is a lie at least ATM it is only an immutable
view of a mutable collection.

Collections
val chars = mapOf("Terion" to "Lannister", "John" to "Snow") 
chars["Terion"] 
chars["Aria"] = “Stark"
 
 
val chars2 = mutableMapOf<String,String>() 
chars2["A girl"] = "has no name" 
 
val sigils = listOf("Direwolf", "Lion", "Dragon", "Flower") 
println(sigils[0])

Kotlin 1.1
❖ Java 7/8 support -> generate J8 class ﬁles
❖ Coroutines : async / await (stackless continuations)
❖ Generators: Yield
❖ inheritance of data classes

Generators (yield)
val fibonacci: Sequence<Int> = generate {
yield(1) // first Fibonacci number
var cur = 1
var next = 1
while (true) {
yield(next) // next Fibonacci number
val tmp = cur + next
cur = next
next = tmp
}
}

Taking Kotlin to production, Seriously

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