Careeroza

Real World Example

Formatting Helpers in a Shopping App

Example

Indian apps format prices in rupees with the Indian grouping (1,23,456) and validate inputs. Extensions make call sites read like English.

fun Long.toRupees(): String {
    val s = this.toString()
    if (s.length <= 3) return "Rs $s"
    val last3 = s.takeLast(3)
    val rest = s.dropLast(3).reversed().chunked(2).joinToString(",").reversed()
    return "Rs $rest,$last3"
}

fun String.isValidIndianMobile() = length == 10 && first() in '6'..'9' && all { it.isDigit() }

fun String.isValidPincode() = matches(Regex("[1-9][0-9]{5}"))

val Int.percentOff: String get() = "$this% OFF"

fun main() {
    println(999L.toRupees())
    println(123456L.toRupees())
    println(12345678L.toRupees())
    println("9876543210".isValidIndianMobile())
    println("1234567890".isValidIndianMobile())
    println("500032".isValidPincode())
    println(40.percentOff)
}

Output

Rs 999
Rs 1,23,456
Rs 1,23,45,678
true
false
true
40% OFF

Android View and Context Extensions

Almost every Android codebase has a small file of extensions like these (Android KTX from Google is a whole library of them).

fun View.show() { visibility = View.VISIBLE }
fun View.hide() { visibility = View.GONE }

fun Context.toast(message: String, long: Boolean = false) =
    Toast.makeText(this, message, if (long) Toast.LENGTH_LONG else Toast.LENGTH_SHORT).show()

fun Fragment.hideKeyboard() {
    val imm = requireContext().getSystemService<InputMethodManager>()
    imm?.hideSoftInputFromWindow(requireView().windowToken, 0)
}

// Usage inside an Activity
binding.progressBar.show()
toast("Added to cart")