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?

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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, 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 operations, 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

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108: State of React Native for Android with Ryan Salva

In this episode Donn talks to React Native magician Ryan Salva. React native and cross-platform development is typically one of our most requested topics so we kick the new year off with React Native. Ryan and Donn dive into the state of React Native today for mobile development, how it’s matured since inception, what kinds of apps are suited to be built with React Native, what kinds aren’t, what are the benefits to using React Native, some tips like pushing updates without having to upload to the play store every time and so much more.

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Show Notes

Misc

Noteworthy quotes from this episode:

As developers, we are empowered to break things; it’s our god given right!

.

Javascript is a beautiful disaster

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