• Kotlin
  • pattern matching
  • nullability
    • late-initialized variable
    • access field in nullable variable
  • anonymous function
  • suspend function
  • Misc

Kotlin

pattern matching

when (var0) {
    LITERAL -> // …
    in 0..5 -> // …
    is TYPE -> // …
    else -> // …
}

nullability

declare nullable variable

var0: TYPE?

late-initialized variable

lateinit var var0: Type0

• no need for null check when accessing
• crash at runtime if no initialized

access field in nullable variable

return null if var0 is null using safe-call operator

var0?.field

assume not-null using non-null assertion operator

var0!!.field

return default_var0 if null using Elvis operator

var0?.field ?: default_var0

anonymous function

refer to existing function

fun fn0(arg0: TYPE0): RETURN_TYPE0 {
    // …
}

val lambda0: (TYPE0 -> RETURN_TYPE0) = ::fn0

create anonymous function directly

val lambda0: (TYPE0 -> RETURN_TYPE) = { arg0 ->
    // …
}

or refer to the only argument as it

val lambda0 = {
    doStuffWith(it) // …
}

call function using trailing lambda syntax

fnUsingLambda(arg0) {
    // Body of anonymous function.
}

suspend function

suspend fun fn0(arg0: TYPE0): RETURN_TYPE0 {
    // …
}

• can only call in a CoroutineScope, execute seemingly sequentially

  • brainless scope GlobalScope

  • scope of current function

    val scope = CoroutineScope(Job())
    

  • android UI component can use

    val scope = MainScope()
    

• can be started in background using launch or async of a CoroutineScope

• use context to choose Dispatcher:

  withContext(Dispatchers.IO) {/*IO tasks*/}
  withContext(Dispatchers.Default) {/*CPU tasks*/}
  

Misc

prettry print Arrays: .contentToString()