Kotlin Conf 2018

As a software developer at Steelcase I’m able to attend a conference a year. This year I purchased tickets to the second ever Kotlin Conference! Over the course of 3 days I learned an immense amount about Kotlin, coroutines, and multiplatform projects. What follows is a massive brain dump of all the notes and highlights that I took during the conference.

Coroutines

• Kotlin equivalent of C# async/await. (suspend = async; await is implied); can declare scope as main and coroutine will avoid blocking UI thread .
• Async alternatives include AsyncTask, Executors, Loaders (deprecated), Promises (API 24+), Threads, and Libraries (i.e. RxJava)
• Not currently supported by Robolectric . Testing still possible with “runBlocking {…}” lambda which forces synchronous execution.
• You can explicitly prepend “async” to a suspend function call in order to immediately return your response type wrapped in a ”Deferred” object.
• You can unwrap a “Deferred” object by call “.wait” .
• For a list of “Deferred” you can unwrap them in 1 of 2 ways:
  • deferredList.map { it.await() } sequentially executes waits
  • awaitAll(deferredList) executes waits in parallel.
• Requires:
  • kotlin_version = ‘1.3.0-rc-116’,
  • org.jetbrains.kotlinx:kotlinx-coroutines-core:0.30.1
  • org.jetbrains.kotlinx:kotlinx-coroutines-android:0.30.1

Multiplatform Projects

• For interoperability you can compile a Kotlin Library (.klib) into a native iOS ObjC Library (with code completion in Xcode!) or call it directly from Android.
• You can also import existing C libraries into either platform.
• Issues with iOS MPP
  • No generics, protected access is broken, enums still somewhat broken.
  • No iOS bitcode support (bitcode must be turned off for the entire iOS project)
  • No step-through debugging of shared libraries in Xcode (Android Studio is fine)
  • Threading is platform specific. Coroutines are not ready for MPP yet
  • No Date object support since Date objects are platform specific.
  • No mocking or dependency injection libraries are available for shared libraries.
  • Crashlytics stack trace reporting give only method names, no line numbers.
  • Overall poor documentation and esoteric setup.
• More information available here.

Kotlin Unit Testing

• Best practice is to use immutability, non-nullability, and non-static constants as much as possible.
• Use of data classes provide ’equals()’ implementation for free, allowing you to easily compare an expected object with the generated object, increasing testing accuracy over attribute comparisons.
• Data classes also provide ‘copy()’ implementation for free, allowing you to generate a deep copy of an object and selectively specify attributes that you want to change in the copy.
• Recommended test stack of JUnit5, MockK, and Kluent.
• JUnit5 provides the following:
  • Allows use of backticks for test names with spaces, i.e. ”fun `user clicks and updates list`()”
  • Allows use of @Nested inner classes for better organization of unit tests.
  • Allows combination of @ParameterizedTest and Stream.of(…) with a custom Data Class TestClass(actual,expected) for one line assertions that give specific failures
• MockK implicitly applies “open” keyword to classes under test (Kotlin classes are final by default)
• Kluent provides fluent assertions.

Kotlin for Graphics by Romain Guy

• Use KTX for purposes of ColorInt extensions to enable clean bit-shifting
• Use Kotlin operators for vector & matrix intersection (“or”), symmetric difference (“xor”), and union (“and”)
• Use the “contains()” operator for geometric class extension functions for clean collision detection
• Use range operators for creating & executing clean & concise geometry extension functions.
• Geometries should be immutable and functions pure.

• Use aggregate functions like “all(…)” (which applies a flatmap of the && operator) and “any(…)” (which applies a flatmap of the

  operator) for cleaner logic

• Use inline classes wherever possible as zero-cost abstractions (just be aware of functions that cause autoboxing operations that nullify this benefit, i.e. ==).