165: Learning Kotlin: Lambda Expressions Part 1


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In this episode, Donn talks about Kotlin Lambda Expressions. He explains the syntax and how to build a couple of simple lambda expressions with and without type inference and declaration. We wrap up with a small example of passing a small lambda with multiple values to a function. See the show notes below for more info. This is part 1 of a multi-part series on Lambda Expressions in Kotlin.

The basic syntax of a lambda expression: kotlin
val myLambda : Type = { argumentList -> codeBody }

The codeBody is the only section that is not optional.

Double lambda expression (doubles an integer) with type inference kotlin
val double = { number: Int -> number * 2 }
val result = double(4)
// result = 8 now

Double string multi-line lambda with type inference. kotlin
val doubleString = { number: Int ->
// codebody
val doubleResult = number * 2
doubleResult.toString()
// Kotlin knows this will return a string
}

Type declaration in a lambda kotlin
val myLambda: (String, Int) -> String = { str, int ->
"$str - ${int.toString()}" // "Donn - 32"
}
val result = myLambda("Donn", 32)
// result = "Donn - 32"

Preview of next week … passing a lambda to a function `\kotlin fun doWork(name: String, favoriteNumber: Int, someLambda: (String, Int) -> String) { // Do some processing, this is a contrived example val repeatedString = “$name$name” val result = someLambda(repeatedString, favoriteNumber) println(result) }

// Usage doWork(“Donn”, 32) { str, int -> val someNewValue = “$str is my parameter and so is $int” someNewValue.length.toString() // this is returned }

// ’37’ is printed via println

// Or use it like this, the lambda code body is what can change, this is where the power is at doWork(“Donn”, 32) { name, count -> var result = “” for(i in 1..count) { result += “$name” } result // this is returned }

// loops over and concatinates “Donn” until the favorite number (aka count) is met. // Output looks like: “DonnDonnDonnDonnDonnDonn…” and so on…

`\

164: Learning Kotlin: Sealed Classes


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In this episode, you’ll learn all about Kotlin Sealed classes. Donn walks you through what they are, how to create them, how to use data classes, objects and regular classes to create a restricted type hierarchy.

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150: Learning Kotlin – Returns, Jumps & Labels

Shownotes

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Code

data class Customer(val isPlatinum: Boolean)

fun main() {

    val customer = Customer(false)

    println("Number of points customer has: ${calculatePoints(customer)}")

    // Break out of the loop once we're over 25
    for (i in 1..100) {
        if (i > 25) {
            break
        } else {
            println(i)
        }
    }


    // Skip all even numbers
    for (i in 1..100) {
        if (i % 2 == 0) {
            continue
        } else {
            println(i)
        }
    }


    // Break out of the outer loop (which breaks out of the inner too) using a label
    [email protected] for (i in 1..100) {
        for (j in 100..200) {
            if (j > 150) [email protected] // This will break out of the inner loop and outer loop
            else println("i: $i, j: $j")
        }
    }

    // Continue processing the next outer loop value when a condition is met.
    [email protected] for (i in 1..100) {
        for (j in 100..200) {
            if (j > 150) [email protected] // This will break out of the inner loop and outer loop
            else println("i: $i, j: $j")
        }
    }

    // returns with label
    example1()
    example2()

    println("I'm done processing!")
}

fun calculatePoints(customer: Customer): Int {
    if (customer.isPlatinum) {
        return 100000
    } else {
        return 10
    }
}


fun example1() {
    listOf(1, 2, 3, 4, 5, 6, 7, 8, 9).forEach {
        if (it > 7) {
            return
        } else {
            println(it)
        }
    }
    println("This wont print :( because return exited the bar() function")
}

fun example2() {
    listOf(1, 2, 3, 4, 5, 6, 7, 8, 9).forEach [email protected] {
        if (it > 7) {
            [email protected]
        } else {
            println(it)
        }
    }
    println("This will print! :) return exited the forEach!")
}

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149: Learning Kotlin: inline classes and Type driven design

In this quick fragment, Kaushik talks about the new Kotlin 1.3 experimental feature “inline classes” and how it helps with Type driven design.

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Shownotes

Type driven design resources

Kotlin KEEP

vs typealias

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136: Kotlin Extension Functions

In this fragment episode, Donn talks about Kotlin extension functions. He discusses what they are, how to build them, why they’re useful, how to organize them, visibility and how to call them Java and much more.

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Show Notes

`

import android.view.View

fun View.gone() {
    this.visibility = View.GONE
}

fun View.visible() {
    this.visibility = View.VISIBLE
}

`

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