Kotlin - Expectations vs Reality

Transcript

1. KOTLIN - EXPECTATIONS VS REALITY Piet Pieterse

2. Kotlin - Expectations vs Reality • What compelled us to

   adopt Kotlin • How we went about this • What we learned

3. About us • Small team of dedicated Android developers •

   Share and develop knowledge • Often working on different projects • Projects are frequently long-term

4. Strong focus on maintainability

5. Kotlin "Statically typed programming language for the JVM, Android and

   the browser"

6. Kotlin package com.m2mobi.example import android.content.Context import com.m2mobi.example.R class ExampleKotlinClass(context: Context)

   : ExampleSuperClass(context), ExampleKotlinInterface { // a non-null, read only value val myBoolean: Boolean = context.resources.getBoolean(R.bool.my_boolean) // a nullable variable var myInt: Int? = null override fun onSomethingHappened(text: String): Boolean { myInt = text.toIntOrNull() return myBoolean } }

7. Why Kotlin? • Null safety • Concise • Interoperable •

   Compatible • Awesome

8. Null safety • In the Android SDK, the dreaded null

   is everywhere • This makes NullPointerExceptions a common concern • Easy to fix, right? Just add more 'if'...

9. Null safety class NullabilityExample { var nonNullableString: String = ""

   var statusCode: Int? = 0 fun updateString(nullableString: String?): Int { // this won't fly nonNullableString = nullableString // and neither will this return statusCode } }

10. Conciseness • Boilerplate reduces readability • Code you don’t write,

    you won’t have to read • Code you don’t write, you won’t have to maintain

11. Conciseness public class Person {
 
 private String name;
 


    public Person(String name) {
 this.name = name;
 }
 
 public String getName() {
 return name;
 }
 
 public void setName(String name) {
 this.name = name;
 }
 }

12. Conciseness class Person(var name: String?)

13. Conciseness class Person(var name: String?) data

14. Conciseness class PersonAdapter: RecyclerView.Adapter<ViewHolder>() {
 
 var viewModels: List<Person> =

    emptyList()
 set(value) {
 field = value
 notifyDataSetChanged()
 }
 
 override fun getItemCount(): Int = viewModels.size

15. Interoperability class Person(var name: String?) // from Java...
 public void

    greetPerson(Person person) {
 Toast.makeText(context, "Hello, " + person.getName(), Toast.LENGTH_SHORT).show();
 } person.getName()

16. Interoperability class Person(var name: String?) // from Java...
 public void

    greetPerson(Person person) {
 Toast.makeText(context, "Hello, " + person.getName(), Toast.LENGTH_SHORT).show();
 } person.getName()

17. Interoperability class Person(var name: String?) // from Java...
 public void

    greetPerson(Person person) {
 Toast.makeText(context, "Hello, " + person.getName(), Toast.LENGTH_SHORT).show();
 } person.getName()

18. Compatibility public String readFirstLineFromFile(String path) { BufferedReader br = null;

    FileReader fr = null; String result = null; try { fr = new FileReader(path); br = new BufferedReader(fr); result = br.readLine(); } catch (IOException e) { e.printStackTrace(); } finally { try { if (br != null) br.close(); if (fr != null) fr.close(); } catch (IOException ex) { ex.printStackTrace(); } } return result; }

19. Compatibility public String readFirstLineFromFile(String path) {
 try (BufferedReader br =

    new BufferedReader(new FileReader(path))) {
 return br.readLine();
 } catch(IOException ioe) {
 return "";
 }
 }

20. Compatibility fun readFirstLineFromFile(path: String): String {
 return try {
 BufferedReader(FileReader(path)).use

    { br -> br.readLine() }
 } catch (ioe: IOException) {
 ""
 }
 }

21. Awesome fun getAverageAgeOfJakesOver67(): Double { return listOfPeople .filterNotNull() .filter {

    it.name == "Jake" && it.age >= 67 } .map { it.age } .average() }

22. Awesome fun superstitiouslyLogABunchOfNumbers() {
 observeABunchOfNumbers()
 .observeOn(AndroidSchedulers.mainThread())
 .filter { it !=

    13 }
 .subscribe {
 Log.d(LOG_TAG, "Ooh, it's number $it")
 }
 }

23. Awesome /**
 * Extension method that generates a Toast and

    shows it
 *
 * @param[text] Text to display
 * @param[duration] Duration of [Toast] (defaults to [Toast.LENGTH_SHORT])
 */
 fun Activity.showToast(text: String, duration: Int = Toast.LENGTH_SHORT) {
 Toast.makeText(this, text, duration).show()
 } // Bye bye makeText, say hello to
 showToast("NEVER FORGETTING TO CALL show() AGAIN")

24. How we introduced Kotlin • Discussed within Android team •

    Started with isolated classes within a Java project • Evaluated along the way • Slowly migrated classes over as project progressed

25. Our experiences - The Good • Surprisingly easy to pick

    up • Excellent IDE support (not entirely unexpected) • Language features such as higher-order functions are a game changer • Standard library full of extremely useful helpers • Zero NullPointerExceptions

26. Our experiences - The Meh • There is always a

    learning curve • Writing idiomatic Kotlin takes practice • Code reviews can be tricky with evolving conventions • Refactoring in AS seemed less smart than for Java • Standard library is currently ~10% of the dex limit • With great power…

27. …comes some really dubious code? fun getStringLength(input: String?): Int {


    return when (input) {
 null -> 0
 else -> input.length
 }
 }

28. Our experiences - The Bad • Annotation processing needed work

    • Dagger + Databinding = pain • Failure to compile can in cases be difficult to debug • That’s it?

29. Overall • Not as difficult to wrap your head around

    as RxJava • As of 1.1, annotation processing should be significantly improved • Java is difficult to go back to • I barely remember what a semicolon looks like ;-)

30. Recommended reading Kotlin website Pushing the limits of Kotlin annotation

    processing - Eugenio Marletti Advancing Android Development with Kotlin - Jake Wharton

31. Questions?