Kotlin factory method pattern

An example of a factory method pattern in Kotlin.

Table of contents for design patterns in Kotlin

The factory pattern is used to replace class constructors, abstracting the process of object generation so that the type of the object instantiated can be determined at run-time. Wikipedia

Example:

Theme

data class Theme(val name: String, val textColor: String, val backgroundColor: String)

ThemeOption

enum class ThemeOption {
    LIGHT,
    DARK,
    AUTO
}

ThemeFactory

object ThemeFactory {

    private val light get() = Theme("Light", "#000000", "#FFFFFF")
    private val dark get() = Theme("Dark", "#FFFFFF", "#000000")
    private fun auto() = if (Calendar.getInstance().get(Calendar.HOUR_OF_DAY) in 0..7) {
        dark
    } else {
        light
    }

    fun themeFor(themeOption: ThemeOption) = when (themeOption) {
        ThemeOption.LIGHT -> light
        ThemeOption.DARK -> dark
        ThemeOption.AUTO -> auto()
    }
}

Usage

fun main() {
    val themeLight = ThemeFactory.themeFor(ThemeOption.LIGHT)
    val themeDark = ThemeFactory.themeFor(ThemeOption.DARK)
    val themeAuto = ThemeFactory.themeFor(ThemeOption.AUTO)
    println(Date())
    println(themeLight)
    println(themeDark)
    println(themeAuto)
}

Result

Mon Aug 17 22:33:41 NOVT 2020
Theme(name=Light, textColor=#000000, backgroundColor=#FFFFFF)
Theme(name=Dark, textColor=#FFFFFF, backgroundColor=#000000)
Theme(name=Light, textColor=#000000, backgroundColor=#FFFFFF)

kotlin pattern