Chapter 5: Data Types and @prop Decorator

Data types

The data types used by the TicTacToe contract include:

  1. boolean: true or false

  2. bigint: arbitrarily large signed integer

  3. PubKey：public key

  4. Sig：signature

  5. ByteString: bytes

If you want to know more data types, you can reference the documentation.

FixedArray

sCrypt only allows fixed-size array. When you declare an array, you must use FixedArray<T, N>. T is the type of array element and N is the array size.

let a: FixedArray<bigint, 3> = [0n, 1n, 2n];
const b: FixedArray<boolean,  3> = [false, false && true, (1n > 2n)];

@prop decorator

Use this decorator to mark any property that intends to be stored on chain. This decorator accepts a boolean parameter. By default, it is set to false, meaning the property cannot be changed after the contract is deployed. If it is true, the property is a so-called stateful property and its value can be updated in subsequent contract calls. Only specific types can be used in @prop.

Contract properties without the @prop decorator are regular TypeScript properties without any special requirement, meaning they can use any type. But accessing these member variables is prohibited in methods decorated with @method.

class Test extends SmartContract {
  @prop()
  x: bigint;

  @prop(true)
  y: FixedArray<boolean, 2>;

  @prop(false)
  z: ByteString;

  // define a constant
  @prop()
  static readonly N: bigint = 3n;  // suffix `n` means bigint literal.

  constructor(x: bigint, y: FixedArray<boolean, 2>, z: ByteString) {
    super(...arguments);
    this.x = x;
    this.y = y;
    this.z = z;
  }

  @method()
  public unlock(x: bigint) {
    assert(this.x === x, "incorrect input x");
  }
}

Put it to the test

The tic-tac-toe game contract supports two players and their public keys need to be saved.

  1. Add the following contract properties:

    • Two stateless properties alice and bob, both of which are PubKey type.
    • Two stateful properties:
      • is_alice_turn: a boolean. It represents whether it is alice's turn to play.
      • board: a fixed-size array FixedArray<bigint, 9> with a size of 9. It represents the state of every square in the board.
    • Three constants:
      • EMPTY, type bigint, value 0n. It means that a square in the board is empty
      • ALICE, type bigint, value 1n. Alice places symbol X in a square.
      • BOB, type bigint, value 2n. Bob places symbol O in a square.

  2. Initialize all non-static properties in the constructor. Specifically, the entire board is empty at first.

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