Using Kotlin in Production

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Using Kotlin in Production @emmaguy

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

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Convince your team

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Have an offsite Nerd out!

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Convince your manager(s)

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

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Everyone is sold! Let’s go!

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

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Plan

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Decide how to use it

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

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Tests only

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

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

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

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Learn & Adapt

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

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Expect discussions about nullability

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#kotlin-tips

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

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Awesome things

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Kotlin = great for hiring

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

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Extension methods

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

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

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

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Named/default arguments

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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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setUpgradeBannerStyle(true) or setUpgradeBannerStyle(loudStyle = true)

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apply { }

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

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Things we learnt

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“Convert any file you touch” doesn’t work

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There is no ‘static’

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

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Where do I put constants?

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Auto convert is not always your friend

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SAM Conversion

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

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

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

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But, if we convert the interface to Kotlin

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

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