Kotlin Extensions and Higher Order Functions (BlrKotlin Meetup, Feb 2018)

Kotlin's modern features has made it a go-to language for Android Developers. This talk will be focussed on how extension functions and higher order functions can help developers write more declarative code, avoid pitfalls and in the end make their application more reliable. We will also discuss caveats related to these features and how to overcome them to avoid any performance issues.

Transcript

1. KOTLIN EXTENSIONS AND HIGHER ORDER FUNCTIONS JITIN SHARMA
2. WHAT ARE EXTENSION FUNCTIONS ▸ Extensions are functions which can be added to existing classes(not really) ▸ Black magic == Static functions ▸ Less power than member functions ▸ They are meant to remove Utils like classes.
3. fun Double.toFahrenheit() : Double = (this * 1.8) + 32 val f = 34.toFahrenheit() //call like this fun Boolean.toString() : String = "abc" true.toString() //"true"
4. fun Double.toFahrenheit() : Double = (this * 1.8) + 32 val f = 34.toFahrenheit() //call like this fun Boolean.toString() : String = "abc" true.toString() //"true"
5. HIGHER ORDER FUNCTIONS ▸ Hail lambdas ▸ Functionception - Function as a parameter of function and returning a function ▸ Functions can be passed around as objects ▸ Bonus Point: SAM conversions for Java Interfaces
6. HOW TO
7. KOTLIN 101 - REMOVE THEM NULL CHECKS ▸ if (someObject != null) { } ▸ someObject?.let { it-> }
8. WORK WITH `APPLY`! supportActionBar?.apply { setDisplayHomeAsUpEnabled(true) setDisplayShowHomeEnabled(true) } // Use apply to avoid repetition of calling variable // Combine with and apply
9. WORK WITH `APPLY`! supportActionBar?.apply { setDisplayHomeAsUpEnabled(true) setDisplayShowHomeEnabled(true) } fun addTintWithCompat(drawable: Drawable, colorInt: Int): Drawable { return with(drawable) { DrawableCompat.wrap(drawable).apply { DrawableCompat.setTint(this, colorInt) } } } // Use apply to avoid repetition of calling variable // Combine with and apply
10. WORK `WITH` APPLY! // Insert functional programming here :) fun movieListReducer(action: Action, movieListState: MovieListState?): MovieListState { return with(movieListState) { val state = movieListState ?: MovieListState() when (action) { is displayMovies -> { state.copy(movieObjects = action.movieObjects) } else -> state } } }
11. KOTLIN LIBRARIES
12. KOTLIN LIBRARIES
13. KOTLIN LIBRARIES
14. CODE VISIBILITY FOOTPRINT ▸ Koltin can help in reducing visible code by wrapping around functions. ▸ You can move away functions which are not important from visibility point of view.
15. DO IT EFFICIENTLY
16. DO IT EFFICIENTLY Move away methods
17. DIY
18. DO IT YOURSELF // interface for item click // initialize interface // setting interface method on click // getting on click in main class JAVA WAY
19. DO IT YOURSELF // Add a function in parameter of adapter constructor // Invoke listener inside on click // Access listener as lambda in main class KOTLIN WAY
20. inline fun <T> justTry(block: () -> T) = try { block() } catch (_: Throwable) { // log here } GENERAL FUNCTIONALITIES
21. inline fun <T> justTry(block: () -> T) = try { block() } catch (_: Throwable) { // log here } GENERAL FUNCTIONALITIES fun String.toIntOrZero() : Int { var value = 0 justTry { value = this.toInt() } return value }
22. inline fun debugMode(block : () -> Unit) { if (BuildConfig.DEBUG) { block() } }
23. debugMode { StrictMode .setThreadPolicy(StrictMode.ThreadPolicy.Builder() .detectAll() .penaltyLog() .build()) } inline fun debugMode(block : () -> Unit) { if (BuildConfig.DEBUG) { block() } }
24. GOT INTERNET? if (isNetworkStatusAvailable()) { val apiService = ApiClient.client?.create(ApiInterface::class.java) val call = apiService?.discoverMovies(API_KEY) call?.enqueue(this) }
25. GOT INTERNET? if (isNetworkStatusAvailable()) { val apiService = ApiClient.client?.create(ApiInterface::class.java) val call = apiService?.discoverMovies(API_KEY) call?.enqueue(this) }
26. GOT INTERNET? val apiService = ApiClient.client?.create(ApiInterface::class.java) val call = apiService?.discoverMovies(API_KEY) call?.enqueue(this) } withConnection {
27. asyncExecutor( heavyFunction = { MovieApplication.movieDataBase?.movieDao()?.getAll() }, response = { response -> response?.forEach { /**/ }} ) fun <T> asyncExecutor(heavyFunction: () -> T, response : (response : T?) -> Unit) { async(UI) { val data : Deferred<T> = bg { heavyFunction() } response(data.await()) } } FUNCTIONS AS OBJECTS
28. VISIBILITY EXTENSIONS fun View.isVisibile(): Boolean = this.visibility == View.VISIBLE fun View.makeVisible() { this.visibility = View.VISIBLE } fun List<View>.showViews() { this.forEach { view -> view.makeVisible() } }
29. CONTEXT EXTENSIONS fun Context.dpToPx(dp : Int): Float { val displayMetrics = this.resources.displayMetrics return Math.round(dp * (displayMetrics.xdpi / DisplayMetrics.DENSITY_DEFAULT)).toFloat() } fun Context.getColorCompat(@ColorRes colorInt: Int) : Int = ContextCompat.getColor(this, colorInt)
30. GENERAL EXTENSIONS fun ByteArray.convertBytesToBitmap(): Bitmap = BitmapFactory.decodeByteArray(this, 0, size) fun Double.celsiusToFahrenheit() : Double = (this * 1.8) + 32 fun String.convertStringToDate(simpleDateFormatPattern: String): Date? { val simpleDateFormat = SimpleDateFormat(simpleDateFormatPattern, Locale.getDefault()) var value: Date? = null justTry { value = simpleDateFormat.parse(this) } return value }
31. SYNTACTIC SUGARS CAN CAUSE DIABETES ▸ Good looking code may not always be best at performance. ▸ Look for downsides before writing a snippet whose usage may get accelerated.
32. DON’T JUDGE BOOK BY IT’S COVER
33. PUTTING ON THE DETECTIVE HAT
34. BACK TO JAVA WORLD
35. GET IN-LINE Kotlin’s doc for use of Inline Functions Decompiled to Java
36. WHEN CODING
37. LOOK BEFORE CODE ▸ Analyze your code before jumping into code. ▸ Don’t over-engineer. ▸ You may not need extensions or higher order functions. ▸ Performance analyze your code. ▸ Examine before writing, the logic you just wrote may already be present in existing libraries. ▸ Single parameter functions are best candidate for conversion to extension function.
38. CONTEXT EXTENSIONS IN FRAGMENTS AND ACTIVITIES inline fun Context.withConnection(block: () -> Unit) { if (isNetworkStatusAvailable()) { block() } } inline fun Fragment.withConnection(block: () -> Unit) { this.context?.withConnection { block() } } // In Activity withConnection { } //Fragment context?.withConnection {} // In Fragment withConnection { }
39. JUST DON’T fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) { if (BuildConfig.DEBUG) { blockIf.invoke() } else { blockElse.invoke() } } debugOrElse({ StrictMode.enableDefaults() }, { Timber.plant(ReleaseTree())})
40. JUST DON’T fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) { if (BuildConfig.DEBUG) { blockIf.invoke() } else { blockElse.invoke() } } debugOrElse({ StrictMode.enableDefaults() }, { Timber.plant(ReleaseTree())})
41. JUST DON’T fun debugOrElse(blockIf: () -> Unit, blockElse: () -> Unit) { if (BuildConfig.DEBUG) { blockIf.invoke() } else { blockElse.invoke() } } debugOrElse({ StrictMode.enableDefaults() }, { Timber.plant(ReleaseTree())}) if (BuildConfig.DEBUG) { StrictMode.enableDefaults() } else { Timber.plant(ReleaseTree()) }
42. BE SMART - USE ANKO
43. THAT’S IT ▸ https://github.com/jitinsharma/Kotlin.someExtensions ▸ https://android.jlelse.eu/playing-with-kotlin-higher-order- functions-aecce3d72a12 ▸ https://twitter.com/js_2892
44. Q&A