KotlinQuiz2.kt

// implement search function that can be filter by name,priceRange or category
fun List<Product>.search(name: String? = null,
                         priceRange: Pair<Double, Double>? = null,
                         categoryId: String? = null): List<Product> = TODO("Make it happen")

fun List<Product>.search(name: String? = null,
                         priceRange: Pair<Double, Double>? = null,
                         categoryId: String? = null): List<Product> {
    val filteredByName = name?.let { filter { product -> it in product.name } } ?: this
    val filteredByPriceRange = priceRange?.let { filter { product -> product.price in it.first..it.second } } ?: this
    val filteredByCategoryID = categoryId?.let { filter { product -> product.category.id == it } } ?: this

    return (filteredByName intersect filteredByPriceRange intersect filteredByCategoryID).toList()
}

// implement search function that can be filter by name,priceRange or category
fun List<Product>.search(name: String? = null,
                         priceRange: Pair<Double, Double>? = null,
                         categoryId: String? = null): List<Product> {
    return this.filter { product -> name?.let { product.name.startsWith(it) } ?: true }
            .filter { product -> priceRange?.let { product.price in it.first..it.second } ?: true }
            .filter { product -> categoryId?.let { product.category.id == it } ?: true }
}

Admin solution

fun List<Product>.search(name: String? = null,
                         priceRange: Pair<Double, Double>? = null,
                         categoryId: String? = null): List<Product> = this
        .let { filteredList -> if (name != null) filteredList.filter { it.name.startsWith(name) } else filteredList }
        .let { filteredList -> if (priceRange != null) filteredList.filter { it.price in priceRange.first..priceRange.second } else filteredList }
        .let { filteredList -> if (categoryId != null) filteredList.filter { it.category.id == categoryId } else filteredList }