class Polygon(val vertices: List<Point>) {
    val height by lazy { vertices.maxBy(Point::y)!!.y - vertices.minBy(Point::y)!!.y }
    val width by lazy { vertices.maxBy(Point::x)!!.x - vertices.minBy(Point::x)!!.x }

    val edges by lazy { (points + points.first()).zipWithNext(::Line) }

    val area by lazy { edges.sumByDouble { (cur, next) -> cur.x * next.y - cur.y * next.x } / 2 } // shoelace method
    
    val centroid by lazy {
        edges.reduce(Point.Origin) { acc, (cur, next) ->
            acc + ((cur + next) * (cur.x * next.y - next.x * cur.y))
        }
    }
    
    // etc
}

lazy<T>

T

lazy

lazy

fun <T> dataAsFlow(){
    //ValueEventListener impl start
    val type= object : GenericTypeIndicator<List<T>>() {}
    val result = dataSnapshot.getValue(type)
    // emit result
    //ValueEventListener impl end
}

List<HashMap<String, String>>

List<T>

List<Category>

List<T>

kotlin-serialization

build.gradle.kts

Result

sealed

inline

Nothing

this

Nothing

error("foo").hasSurrogatePairAt(1)

this should pass(TestData)[1]

val temp = someMember
someMember = null
temp.close()

someMember

?.

close()

interface IFoo<A>
class Foo: IFoo<String>
class Bar<A>: IFoo<A>

inline fun <reified T: IFoo<*>> createBar(){
   val type = T::class.supertypes[0].arguments[0].type // the type is not lost, String is here

   Bar<type>() // ?? how to use it here
}

createBar<Foo>()

fun <A, T:IFoo<A> createBar()

A

class Holder(override val containerView: View) : ViewHolder(containerView), LayoutContainer {
    fun bind() {
        my_view
    }
}

class Holder(override val containerView: View) : ViewHolder(containerView), LayoutContainer {
    fun bind() {
        containerView.my_view
    }
}

typealias Amount = BigDecimal

Boolean.something<T>(f: () -> T): T?  = if (this) { f() } else null

class Foo<T> {
  fun <U> function() { ... }
}

U

T

List<T>

interface Provider {
  fun <P : X> provide(name: String, clazz: KClass<out P>): P?
}
inline fun <reified P : X> Provider.provide(name: String): P? =
  provide(configName, P::class)

@Deprecated

@Deprecated(
  message = "Direct usage of provide(name, clazz) is discouraged",
  level = DeprecationLevel.WARNING,
  replaceWith = ReplaceWith(
    expression = "???",
    imports = ["com.example.provider.provide"]
  )
)

myProvider.provide("asdf", MyData::class)

provide(name)

provide("asdf")

provide<clazz>(name)

myProvider.provide<clazz>("asdf")

clazz

myProvider.provide<MyData>("asdf")

myProvider.provide("asdf")