Using Kotlin in Production

Kotlin has fast become the new hotness in the Android world - but what is the reality of adding it to an app which is rapidly being built for a fast growing startup? In this talk we'll cover how we went about adding Kotlin to the Monzo app, why we made those choices and how it went.

https://devfest.gdg.london/schedule/2017-11-11?sessionId=204

Transcript

1. Using Kotlin in Production
   @emmaguy
   

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2. How did we get there?
   Did it go well?
   Lessons learnt
   

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3. Convince your team
   

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4. Have an offsite
   Nerd out!
   

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5. Convince your manager(s)
   

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7. Christina Lee @ Google I/O
   https://www.youtube.com/watch?v=fPzxfeDJDzY
   

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8. Everyone is sold! Let’s go!
   

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9. “Let’s just start using it”
   - me, March 2017
   

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10. Plan
    

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11. Decide how to use it
    

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12. Only tests?
    A layer of your application’s architecture?
    ‘Anything new’?
    

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13. Tests only
    

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14. @Test
    public void register_noPhoneNumber_showContactSupport() {
    when(pinManager.fetchPhoneNumber()).thenReturn("");
    presenter.register(view);
    verify(view).showContactSupport();
    }
    

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15. @Test
    fun register_noPhoneNumber_showContactSupport() {
    whenever(pinManager.fetchPhoneNumber()).thenReturn("")
    presenter.register(view)
    verify(view).showContactSupport()
    }
    

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16. Figure out any potential “incompatibilities”
    e.g. Realm, Lombok
    

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19. Learn & Adapt
    

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20. Progressed to use in data layer of our app
    ...then in Activities (replacing ButterKnife)
    ...then anything new!
    

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21. Expect discussions about nullability
    

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22. #kotlin-tips
    

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23. Stick with what you committed to for a while
    Assess
    Make changes
    

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25. Awesome things
    

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26. Kotlin = great for hiring
    

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27. @Deprecated
    https://hackernoon.com/how-kotlins-deprecated-relieves-pain-of-colossal-refactoring-8577545aaed
    

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28. Extension methods
    

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29. @Override
    public void showLoading() {
    progressBar.setVisibility(View.VISIBLE);
    }
    or
    override fun showLoading() {
    progressBar.visible()
    }
    

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30. fun ImageView.loadUrl(url: String) {
    Picasso.with(context).load(url).into(this)
    }
    imageView.loadUrl(url)
    

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31. fun Activity.screenWidth(): Int {
    val metrics = DisplayMetrics()
    windowManager.defaultDisplay.getMetrics(metrics)
    return metrics.widthPixels
    }
    

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32. Named/default arguments
    

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33. fun card(
    id: String = UUID.randomUUID().toString(),
    expires: String = "24/20",
    cardStatus: CardStatus = CardStatus.ACTIVE
    ): Card {
    return Card(id, expires, cardStatus)
    }
    Card(expires = "03/16", cardStatus = CardStatus.INACTIVE)
    

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34. setUpgradeBannerStyle(true)
    or
    setUpgradeBannerStyle(loudStyle = true)
    

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35. apply { }
    

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36. val arguments = Bundle().apply { putString(KEY_ID, id) }
    

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37. Things we learnt
    

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38. “Convert any file you touch” doesn’t work
    

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39. There is no ‘static’
    

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40. companion object {}
    https://medium.com/@BladeCoder/exploring-kotlins-hidden-costs-part-1-fbb9935d9b62
    

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41. Where do I put constants?
    

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43. Auto convert is not always your friend
    

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45. SAM Conversion
    

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46. public interface PayeeClickListener {
    void onPayeeClicked(Payee payee);
    }
    

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47. adapter.setPayeeClickListener(payee -> /* do something */);
    

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48. adapter.setPayeeClickListener(PayeeClickListener { /* do something
    */ })
    

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49. But, if we convert the interface to Kotlin
    

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50. adapter.setPayeeClickListener(object : PayeeClickListener {
    override fun onPayeeClicked(payee: Payee) {
    // do something
    }
    })
    

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51. New thing = less mature ecosystem
    IDE integration, style guide, code coverage tools
    

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52. Would you do it again?
    

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53. Absolutely.
    

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55. Thank you!
    @emmaguy
    

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56. Questions?
    @emmaguy
    

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