I'm Nasreen

Software engineer at Toast
Mostly Android
Originally Java, increasingly using Kotlin
Kiosk

3 things I like about Kotlin

1) Handling nulls
2) Functional collection methods
3) Extension functions

Some features I used when converting from Java

1) Null views in Android

view?.displayInvalidCardErrorMessage()

if (view != null) {
    view.hideProgressSpinner();
}

Kotlin:

Java:

Cases in Android where we must check the view is not null
Kotlin makes this
- more succinct + readable
- forces null checks when type is nullable

2) Functional collections methods

Refactored from Java -> Kotlin
FluentIterable
Kotlin collections methods

Functional collections methods

fun Check.getFirstOpenCreditCardPayment(): Optional<Payment> {
    return Optional.fromNullable(payments.firstOrNull { payment ->
            payment.paymentType == Payment.Type.CREDIT &&
                    !payment.isDeleted &&
                    payment.paymentStatus == Status.OPEN })
}

private Predicate<Payment> isOpenCreditCard = payment -> {	
    return payment.paymentType == Payment.Type.CREDIT 
        && !payment.isDeleted() 
        && payment.paymentStatus == Status.OPEN;	
};

private Optional<Payment> getFirstPayment(Check check, Predicate condition) {	
    Optional<ToastPosOrderPayment> result = FluentIterable.from(check.payments)	
                .filter(condition)	
                .first();	
    return result;	
}
    
public Optional<Payment> getFirstOpenCreditCardPayment(Check check){	
    return getFirstPayment(check, isOpenCreditCard);	
}

FluentIterable:

Kotlin built in collections methods:

3) Extension Functions

Write new functions for a class without altering or extending it
String, third party classes

fun CardReaderService.canTakeEmvPayment(): Boolean {
    return (canTakeQuickChipPayment() || canTakeFullEmvPayment())
}

in KioskCardReaderServiceExtensionFunctions.kt

Understand CardReaderService from the perspective of the kiosk workflow
Avoid adding specific utility methods to a generic service

A Seamless Journey into the Awesome World of

Wifi Name: Toast-Guest
Password: welcometotoast

Tom Hanley

Senior Software Engineer @

Organiser of the Dublin Kotlin User Group

Huge fan of Kotlin

What is Kotlin?

General purpose programming language
Statically typed
Targets the JVM
- Can also compile to Javascript
- Can also be compiled to native binaries
Developed by JetBrains

Kotlin History

Started in 2010 by JetBrains
They had a huge Java codebase
Wanted a modern expressive language
None of the existing languages were a good fit

Kotlin Design Goals

100% Java Interoperability
More readable than Java
Less error prone than Java
More productive than Java
Way simpler than Scala
Pragmatic
- Not a research project
- No ground breaking features
- Best features established in other languages: groovy, scala, c#

"The primary goal of Kotlin is to provide a more concise, more productive, safer alternative to Java that’s suitable in all contexts where Java is used today"

2010: Work begins on Kotlin
2011: Kotlin is open sourced
2016: Kotlin 1.0 released
2017: Google announce Kotlin has first class support on Android

Kotlin Timeline

2018
- The fastest growing language in 2018
  - 2.6x the number of github contributors
- One of the most loved languages of 2018
- 5-10 years ahead of Java
2019
- Google recommends:
  - "If you're starting a new project, you should write it in Kotlin"

Kotlin Timeline

IN

Toast Restaurant Platform

We are a restaurant company
Our core products are cloud POS systems and CC payments processing
All of our in-restaurant technology is on Android tablets
Web interface for managing restaurants
Consumer-facing websites and apps for online ordering
APIs for integrations with dozens of restaurant technology partners

Toast at a Glance

250-person R&D team
Tens of thousands of customers in the US
Processing billions in payments every year
July 2013: First live customer
April 2019: $250 million in Series E funding at $2.7 billion valuation
< 10% US POS market share so far
Lots more growth to come!

2018: Revenue up 148%

Before Toast...

I was a Java developer
- Java 8
- Big fan of functional programming
Met a friend at a Dublin Java User Group meetup

Shortly after...

I started looking into Kotlin
Youtube "Kotlin for Java Programmers" by Venkat Subramaniam
- "The took Java and decided to add all the good features they could find, and then they called it Kotlin"
- "Fluent, elegant syntax"
- "Wonderful features from a lot of different languages"
- "A dream come true"

Some time later...

I started working in Toast!
Guest and restaurant-facing Android tablets
- Java & Kotlin
Backend services
- Java 8 Dropwizard Services
- Kotlin being used as well
Internal, guest-facing and restaurant-facing web apps
- Play monolith -> Angular/React

Not long after...

I was working on the receipts team.
- Printed receipts (mobile)
- Digital receipts (web)
- 1.3 million receipts a day
Refactoring project to extract and rewrite all this code to a shared library.
- This was all Java

Android Restrictions

We're restricted to Java 7 on android?
I can't use Java 8 streams?
- This sucks.
- Ok, I guess you can use guavas FluentIterable and RetroLambda, but they're far from elegant
- Hold on a second, theres no group by operator in guava?
I saw some Kotlin somewhere in the mobile app, that means I can convert this all to Kotlin, right?

That weekend...

I converted everything to Kotlin
- Turns out this is super easy
- Intellij really helps you along
Great functional programming features
- Beautiful streams library
- Immutability is the default
- Final is the default
I showed the team some before and after highlights
Kotlin sells itself

But how does all this modern streams stuff work on Java 7 restricted android devices?

Turns out the Kotlin compiler is awesome!
- Kotlin can be compiled to any Java version bytecode
- Kotlin can even be compiled to Javascript
- Kotlin can even be compiled to native binaries for iOS, OSX, Windows, Linux etc.

What if the code isn't as performant as Java?

Not a problem!
- Kotlin and Java can live side by side
- Java can call Kotlin, Kotlin can call Java, SEAMLESS
- If you find a place where Java is faster, write it in Java

What about the additional cognitive load to learn a new language?

Its super easy to get up and running
Its designed for Java developers
Its a simpler and safer language than Java
Its more readable, and more productive than Java

For a much more detailed argument for Kotlin see:
Doc by Jake Wharton

Full steam ahead with Kotlin!

Kotlin is a better language for the JVM than Java
- Really easy to get up and running
- Simpler language than Java
- Much safer than Java
  - No more NullPointerExceptions!
  - Streamlines the handling of null values
- Much more clean & concise than Java
- 100% Interoperable with Java
  - Kotlin & Java classes can live side by side

To Summarise

Getting started

Intellij auto-convert to Kotlin
- Really helps that Jetbrains created Intellij and Kotlin
- Caveat: you need to be careful with nullability
Writing Java in Kotlin
- Which is fine
- Gradually learn more idomatic Kotlin
Discover the std lib tools with autocomplete
- Quickly learn that the stdlib is fantastic
- Google "is there a more Kotlin way to do this"
The online documentation is great

val myString: String? = null

println(myString.isNullOrEmpty()) // prints true!

Discovering awesome features

Concise?

public class Person {

    private final String firstName;
    private final String lastName;

    public Person(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        Person person = (Person) o;

        if (firstName != null ? !firstName.equals(person.firstName) : person.firstName != null) {
            return false;
        }
        return lastName != null ? lastName.equals(person.lastName) : person.lastName == null;
    }

    @Override
    public int hashCode() {
        int result = firstName != null ? firstName.hashCode() : 0;
        result = 31 * result + (lastName != null ? lastName.hashCode() : 0);
        return result;
    }

    @Override
    public String toString() {
        return "Person{" +
                "firstName='" + firstName + '\'' +
                ", lastName='" + lastName + '\'' +
                '}';
    }
}

Concise!

data class Person(
    val firstName: String, 
    val lastName: String
)

Covers all of the language features really well and in a lot of depth
Written by two members of the Kotlin team
- Svetlana Isakova & Dimitri Jemerov

Big chunks of this book obviated by Kotlin features

Let's get everyone using Kotlin!

Some of the meetups we organised

Kotlin Koans
Drone delivery app
Ktor for web services
Using coroutines in your android app
Create a Kotlin-React app
Kotlin Katas
Build an Alexa skill in Kotlin
Kotlin Coroutines Case Study & Lessons Learned
Kotlin Room with a View

Kotlin Koans

A series of exercises to get you familiar with the Kotlin syntax and features
The best way to learn all the language features
Written by Svetlana Isakova
- Also wrote Kotlin in Action and Atomic Kotlin

Kotlin Koans Introduction Section

Koans Introduction

Hello World
Java to Kotlin conversion
Named Arguments
Default Arguments
Lambdas
Strings
Data Classes
Nullable Types
Smart Casts
Extension Functions
Object Expressions

Getting set up

Highly recommend you use Intellij
- Comes bundled with Kotlin & great tools
Install the EduTools plugin
- Preferences -> Plugins -> Install Jetbrains plugins
- Search EduTools, install & restart Intellij
- Select Learner if prompted on restart
File > Browse courses and select Kotlin
Refresh your gradle dependencies
Find a pair to work with!

I'm Nasreen

3 things I like about Kotlin

1) Null views in Android

2) Functional collections methods

Functional collections methods

3) Extension Functions

A Seamless Journey into the Awesome World of

Wifi Name: Toast-Guest Password: welcometotoast

Tom Hanley

Senior Software Engineer @

Organiser of the Dublin Kotlin User Group

Huge fan of Kotlin

What is Kotlin?

Kotlin History

Kotlin Design Goals

"The primary goal of Kotlin is to provide a more concise, more productive, safer alternative to Java that’s suitable in all contexts where Java is used today"

Kotlin Timeline

2018

2019

Kotlin Timeline

IN

Toast Restaurant Platform

Toast at a Glance

Before Toast...

Shortly after...

I started looking into Kotlin

Youtube "Kotlin for Java Programmers" by Venkat Subramaniam

Some time later...

Not long after...

Android Restrictions

That weekend...

But how does all this modern streams stuff work on Java 7 restricted android devices?

What if the code isn't as performant as Java?

What about the additional cognitive load to learn a new language?

For a much more detailed argument for Kotlin see: Doc by Jake Wharton

Full steam ahead with Kotlin!

To Summarise

Getting started

Discovering awesome features

Concise?

Concise!

Let's get everyone using Kotlin!

Some of the meetups we organised

Kotlin Koans

Kotlin Koans Introduction Section

Koans Introduction

Getting set up

For anyone finished early

Thank you

A Seamless Journey into the awesome world of Kotlin - Workshop

More from Tom Hanley

Wifi Name: Toast-Guest
Password: welcometotoast

For a much more detailed argument for Kotlin see:
Doc by Jake Wharton