Kotlin - lambdas and higher-order functions - Treating Code Like Data - list, search, passing function parameter values

Head First Kotlin
A Brain-Friendly Guide
楽天ブックス(Kobo) 紀伊國屋書店(Kinoppy)

開発環境

• macOS Mojave - Apple (OS)
• Windows 10 Pro (OS)
• IntelliJ IDEA CE(Community Edition) (IDE(統合開発環境))
• Kotlin (プログラミング言語)

Head First Kotlin: A Brain-Friendly Guide (Dawn Griffiths(著)、David Griffiths(著)、O'Reilly Media)のChapter 11(lambdas and higher-order functions - Treating Code Like Data)、Code Magnets(356)の解答を求めてみる。

コード

data class Grocery(
    val name: String,
    val category: String,
    val unit: String,
    val unitPrice: Double
)

fun search(list: List<Grocery>, criteria: (g: Grocery) -> Boolean) {
    for (l in list) {
        if (criteria(l)) {
            println(l.name)
        }
    }
}

fun main() {
    val groceries = listOf(
        Grocery("Tomatoes", "Vegetable", "lb", 3.0),
        Grocery("Mushrooms", "Vegetable", "lb", 4.0),
        Grocery("Bagels", "Bakery", "Pack", 1.5),
        Grocery("Olive oil", "Pantry", "Bottle", 6.0),
        Grocery("Ice cream", "Frozen", "Pack", 3.0)
    )
    println("Expensive ingredients:")
    search(groceries) { i: Grocery -> i.unitPrice > 5.0 }
    println("All vegetables:")
    search(groceries) { i: Grocery -> i.category == "Vegetable" }
    println("All packs:")
    search(groceries) { i: Grocery -> i.unit == "Pack" }
}

入出力結果

Expensive ingredients:
Olive oil
All vegetables:
Tomatoes
Mushrooms
All packs:
Bagels
Ice cream

Process finished with exit code 0