Chapter 4: sCrypt Smart Contracts

A smart contract is a class that extends the SmartContract base class. A simple example is shown below.

import { SmartContract, method, prop, assert } from "scrypt-ts";

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

  constructor(x: bigint) {
    super(...arguments);
    this.x = x;
  }

  @method()
  public unlock(x: bigint) {
    assert(this.add(this.x, 1n) === x, "incorrect input x");
  }

  @method()
  add(x0: bigint, x1:bigint) : bigint {
    return x0 + x1;
  }
}

Class members decorated with @prop() and @method() will end up on the blockchain and thus must be a strict subset of TypeScript. Undecorated members are regular TypeScript and won't be on-chain. A significant advantage of sCrypt is that both on-chain and off-chain code are written in the same language: TypeScript.

Constructor

A smart contract must have an explicit constructor if it has at least one @prop.

The super() method must be called in the constructor and all the arguments of the constructor should be passed to super in the same order as they are passed into the constructor. For example,

class A extends SmartContract {
  p0: bigint
  
  @prop()
  p1: bigint
  
  @prop()
  p2: boolean
  
  constructor(p0: bigint, p1: bigint, p2: boolean) {
    super(...arguments)  // same as super(p0, p1, p2)
    this.p0 = p0
    this.p1 = p1
    this.p2 = p2
  }
}

arguments is an array containing the values of the arguments passed to that function. ... is the spread syntax.