Chapter 6: @method Decorator

@method decorator

Use @method to decorate any method that intends to run on chain.

Decorated methods can only call methods that are also decorated with @method. Additionally, only properties decorated with @prop can be accessed. Methods not decorated are just regular TypeScript class methods.

They are two types of @methods.

1. Public

Each contract must have at least one public @method. It is denoted with the public modifier and does not return any value. It is visible outside the contract and acts as the main method into the contract (like main in C and Java).

A public @method can be called from an external transaction. The call succeeds if it runs to completion without violating any conditions in assert(). Function assert(condition: boolean, errorMsg?: string) throws an error if the condition is false; otherwise it does nothing. An example is shown below.

@method()
public unlock(x: bigint) {
    // only succeeds if x is 1
    assert(1n === x, "unequal");
}

2. Non-public

Without a public modifier, a @method is internal and cannot be directly called from an external transaction.

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

Put it to the test

Add methods to contract TicTacToe:

1. Public @method move() : Alice and Bob each locks X bitcoins in a UTXO containing contract TicTacToe. Next, they alternately play the game by calling move() with 2 parameters:

   • n : bigint, which square to place the symbol
   • sig : Sig, a player's signature

2. Non-public method won() : Check if a player has won the game. Returns boolean type with 1 parameter:

   • play : bigint, which square to place the symbol

3. Non-public method full() : Checks if all squares of the board have symbols. Returns boolean type, no parameter.

Add assert() in move(), requiring function parameter n must be greater than or equal to 0n and less than 9n.