150: Learning Kotlin – Returns, Jumps & Labels

Shownotes

Download

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
    donn@ for (i in 1..100) {
        for (j in 100..200) {
            if (j > 150) break@donn // 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.
    donn@ for (i in 1..100) {
        for (j in 100..200) {
            if (j > 150) continue@donn // 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 bin@ {
        if (it > 7) {
            return@bin
        } else {
            println(it)
        }
    }
    println("This will print! :) return exited the forEach!")
}

Sponsors 🙏

  • Nevercode

    • Nevercode is taking Flutter revolution extremely serious and is prepared to offer kick-ass CI/CD for Flutter projects with codemagic.io. Check it out and get started at https://codemagic.io/
  • Sentry.io

    • Sentry tells you about errors in your code before your customers have a chance to encounter them. Check them out at: https://sentry.io/for/android/

Contact

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.

Download

Shownotes

Type driven design resources

Kotlin KEEP

vs typealias

Sponsors 🙏

Contact

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.

Download

Show Notes

`

import android.view.View

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

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

`

Contact

116: Learning Kotlin – inline, noinline and crossinline

In this episode of learning kotlin, we look at 3 important keywords – inline, noinline and crossinline. The inline keyword is super common and you’ve probably run across this one at some point. What does it mean and when is it useful? We also look at the related but seldom used variants noinline and crossinline.

Download directly

Show Notes

Code Snippets:

Simple inlined function:

// Kotlin 
fun main(args: Array<String>) {
    functionA()
}

inline fun functionA() {
    println("awesomeness !")
}

Warning: Expected performance impact of inlining ‘public inline fun functionA() can be insignificant. Inlining works best for functions with lambda parameters

What the code looks like in Java:

public static final void main(String[] args) {
  String var1 = "awesomeness !";
  System.out.println(var1);
}

Function with lambda parameter:

fun main(args: Array<String>) {
    functionA({
        println("double awesomeness")
    })
}

inline fun functionA(lambda: () -> Unit) {
    println("awesomeness !")
    lambda.invoke()
}

What the code looks like in Java (without inline):

public static final void main(String[] args) {
    functionA(new Function() {
      println("double awesomeness")  
    });
}

public static final void functionA(Function0 lambda) {
    String var1 = "awesomeness !";
    System.out.println(var1);
    lambda.invoke();
}

What the code looks like in Java (with inline):

public static final void main(String[] args) {
    String var1 = "awesomeness !";
    System.out.println(var1);
    String var2 = "double awesomeness";
    System.out.println(var2);
}

Function0:

public interface Function0<out R> : Function<R> {
    /** Invokes the function. */
    public operator fun invoke(): R
}

Misc:

Sponsors

  • Microsoft AppCenter – Sign up now on appcenter.ms and spend less time managing your app lifecycle and more time coding.

Contact

109: Learning Kotlin – Sequences the new Iterables

In this episode of Fragmented, we go back to learning some Kotlin and look at the Iterable like data structure introduced called “Sequences”. What is a sequence? How is it different from Iterable? When should I use it?

Download directly

Show Notes

Eager/Lazy

Eager evaluation:

val lst = listOf(1, 2)
val lstMapped: List<Int> = lst.map { print("$it "); it * it }
print("before sum ")
val sum = lstMapped.sum()

// prints "1 2 before sum"

Lazy evaluation:

val seq = sequenceOf(1, 2)
val seqMapped: Sequence<Int> = seq.map { print("$it "); it * it }
print("before sum ")
val sum = seqMapped.sum()

// prints "before sum 1 2"

Source stackoverflow.com answer

Intermediate and terminal operations

Notice that at each chain operation, a new temporary list is created:

data class Person(val name: String, val age: Int)

fun main(args: Array<String>) {
    val people = 
        listOf(Person("Chris Martin", 31), 
               Person("Will Champion", 32),
               Person("Jonny Buckland", 33),
               Person("Guy Berryman", 34),
               Person("Mhris Cartin", 30))

    println(people
            .filter { it.age > 30 } // new temp. list
            .map {                  
                it.name.split(" ").map {it[0]}.joinToString("")
            }  // new temp. list
            .map { it.toUpperCase() }) // new temp. list
}

Using a sequence:

println(people
        .asSequence()  // convert to sequence
        .filter { it.age > 30 } // lazy eval (intermediate op)
        .map {                  
            it.name.split(" ").map {it[0]}.joinToString("")
        }  // lazy eval (intermediate op)
        .map { it.toUpperCase() }  // lazy eval (intermediate op)
        .toList() // terminal operation
       )

Without a terminal operation, Sequences won’t print anything:

val seq = sequenceOf(1, 2, 3)
println(seq) // prints address
println(seq.toList()) // [1, 2, 3]

You can’t pick an index from a sequence:

println(seq[0]) // throws ERROR "No get method providing array access"
println(seq.toList()[0]) // 1

Sponsors

Contact