第 4 章：集合类型

xs = [1, 2, 3]
xs.append(4)
xs[0] = 10
print(len(xs), xs[-1])

val xs = mutableListOf(1, 2, 3)
xs.add(4)
xs[0] = 10
println("${xs.size} ${xs.last()}")

const xs: number[] = [1, 2, 3];
xs.push(4);
xs[0] = 10;
console.info(`${xs.length} ${xs[xs.length - 1]}`);

point = (10, 20)
x, y = point
# point[0] = 1  # TypeError

val point = 10 to 20   // Pair
val (x, y) = point
// data class 更常见

const point: [number, number] = [10, 20];
const [x, y] = point;

user = {"id": 1, "name": "Ada"}
user["name"] = "Bob"
print(user.get("email", "n/a"))
for k, v in user.items():
    print(k, v)

val user = mutableMapOf("id" to 1, "name" to "Ada")
user["name"] = "Bob"
println(user["email"] ?: "n/a")
for ((k, v) in user) {
    println("$k $v")
}

const user: Record<string, string | number> = { id: 1, name: "Ada" };
user["name"] = "Bob";
console.info(user["email"] ?? "n/a");
for (const k of Object.keys(user)) {
  console.info(k, user[k]);
}

s = {1, 2, 2, 3}   # {1, 2, 3}
s.add(4)
print(2 in s)

val s = mutableSetOf(1, 2, 2, 3)
s.add(4)
println(2 in s)

const s = new Set<number>([1, 2, 2, 3]);
s.add(4);
console.info(s.has(2));

a = [0, 1, 2, 3, 4]
print(a[1:4])    # [1, 2, 3]
print(a[::-1])   # 反转

val a = listOf(0, 1, 2, 3, 4)
println(a.subList(1, 4))
println(a.asReversed())

const a = [0, 1, 2, 3, 4];
console.info(a.slice(1, 4));
console.info([...a].reverse());