Fragmented - Android Developer Podcast

168: Learning Kotlin: Lambda Expressions Part 2

Jul 8, 2019

21:37

In this episode, Donn continues his talks about Kotlin Lambda Expressions. He explains how you can use lambda expressions as function parameters and as return types for functions.

This is a very dense episode - if you get lost look at the code snippets below or view on them on fragmentedpodcast.com


class LogReader {
    fun processFile(file: File, processLine: (String) -> Unit = {}) {
        file.forEachLine {
            println("Number of Chars: ${it.length}")
            processLine(it)
            println("Line Done Processing")
        }
    }

    fun processFileWithHandlers(file: File, logHandler: LogHandler) {
        file.forEachLine {
            println("Start of Processing")
            logHandler.handleLine().forEach { handler -> handler(it) }
            println("Line Done Processing")
        }
    }
}

interface LogHandler {
    fun handleLine(): List<(String) -> Unit>
}


val reader = LogReader()
val textFile = File("/Users/donnfelker/scratch/lorem.txt")

// Process with single lambda
reader.processFile(textFile, { println("First 10 Chars: ${it.substring(0..9)}") })

val logHandler = object : LogHandler {
    override fun handleLine(): List<(String) -> Unit> {
        return listOf<(String) -> Unit>(
            { line -> println("${line.substring(0, 1)}") },
            { line -> println("${line.substring(2, 4)}") },
            { line -> println("${line.substring(5, 10)}") }
        )
    }
}

// Process with multipe handlers via the logHandler
reader.processFileWithHandlers(textFile, logHandler)