Arrays and Tuples

Tuples

Tuples describe arrays with a fixed order and known element types.

tuple A tuple such as `[string, number]` stores values in fixed positions with fixed types.

Tuples

attempts
tuple.ts
Replay: real traced execution (multi-file project)
const attempts: number = 2;
const result: [string, number] = ["login", attempts];

const action: string = result[0];
const count: number = result[1];

console.log(`${action}: ${count}`);

const attempts: number = 1;
const result: [string, number] = ["login", attempts];

const action: string = result[0];
const count: number = result[1];

console.log(`${action}: ${count}`);

const attempts: number = 4;
const result: [string, number] = ["login", attempts];

const action: string = result[0];
const count: number = result[1];

console.log(`${action}: ${count}`);

  1. attempts ← 2, result ← login,2, action ← login, result[0] ← login

    1const attempts→ 2: number = 2;  //@attempts=1, 42const result→ login,2: [string, number] = ["login", attempts2];34const action→ login: string = result[0]→ login;5const count→ 2: number = result[1]→ 2;67console.log(`${actionlogin}: ${count2}`);
    outputlogin: 2

  1. attempts ← 1, result ← login,1, action ← login, result[0] ← login

    1const attempts→ 1: number = 1;2const result→ login,1: [string, number] = ["login", attempts1];34const action→ login: string = result[0]→ login;5const count→ 1: number = result[1]→ 1;67console.log(`${actionlogin}: ${count1}`);
    outputlogin: 1

  1. attempts ← 4, result ← login,4, action ← login, result[0] ← login

    1const attempts→ 4: number = 4;2const result→ login,4: [string, number] = ["login", attempts4];34const action→ login: string = result[0]→ login;5const count→ 4: number = result[1]→ 4;67console.log(`${actionlogin}: ${count4}`);
    outputlogin: 4

Follow the Tuple

  1. attempts starts as 2.
  2. result stores two fixed positions: "login" first, then attempts.
  3. action reads result[0], so it becomes login.
  4. count reads result[1], so it becomes 2.
  5. The program prints login: 2. | tuple position | value | local name | | --- | --- | --- | | result[0] | login | action | | result[1] | 2 | count |

Exercise: tuple.ts

Reproduce login: 2, then use the pinned attempts variants 1 and 4 to predict login: 1 and login: 4.