CODESAMPLE

Pipes and Filters - Kotlin

Pipes and Filters Kotlin

The Pipes and Filters pattern structures a program as a sequence of processing stages (filters) connected by channels (pipes). Each filter has a single responsibility: to transform the data it receives. The pattern promotes reusability, maintainability, and simplifies complex data processing pipelines.

This Kotlin example simulates processing a list of strings through filters. We use Kotlin’s functional programming capabilities – specifically, higher-order functions and lambdas – to concisely define each filter as a transformation operation on a List<String>. The pipe is implicitly handled through function composition using the let scope function, passing the result from one filter to the next. This is idiomatic Kotlin as it leverages immutability and functional programming constructs rather than mutable state, resulting in a cleaner and more readable pipeline.

// Pipes and Filters Pattern in Kotlin

data class DataItem(val value: String)

// Filter 1: Uppercase the string
fun filterUppercase(data: List<DataItem>): List<DataItem> = data.map { it.copy(value = it.value.uppercase()) }

// Filter 2: Remove characters that are not letters or numbers
fun filterAlphanumeric(data: List<DataItem>): List<DataItem> = data.map { it.copy(value = it.value.filter { char -> char.isLetterOrDigit() }) }

// Filter 3: Filter out empty strings
fun filterNotEmpty(data: List<DataItem>): List<DataItem> = data.filter { it.value.isNotEmpty() }

fun main() {
    val inputData = listOf(
        DataItem(" Hello World! "),
        DataItem("123abc456"),
        DataItem(""),
        DataItem("Kotlin Pipes")
    )

    val processedData = inputData
        .let(filterUppercase)
        .let(filterAlphanumeric)
        .let(filterNotEmpty)
    
    println(processedData) // Output: [DataItem(value=HELLO WORLD!), DataItem(value=123ABC456), DataItem(value=KOTLINPIPES)]
}