Tact Hello World

Receivers and Getters

Tact's facts #4

Here we will learn more about existing tools in Tact for defining contract's behavior in general. init() - is one of them, and below listed all of them:

Tactical Practice #4

Declare fun

Ok, one more time, we need extend our contract's behaviour

//previous code
 
fun add(v: Int) {
 
    let ctx: Context = context();
    require(ctx.sender == self.owner, "Invalid sender");
    
    self.counter = (self.counter + v);
}

Declare function add that will do following things:

1. Get incoming integer argument v.
2. Check current incoming message sender is equal to owner we set for contract in deployment process.
3. If this check passed add to current counter value v and update counter value in contract. If required is not pass, throw exception message "Invalid sender".

Declare receivers

//previous code
 
receive(msg: Add) {
    self.add(msg.amount);
  }
}
 
receive("increment") {
    self.add(1);
  }
}

Here we are specified two receive functions. This means, that if we get message in contract that correspond of one the receiver contract execute one of them. In other case, contract will do nothing. receive() function expects an incoming argument of String type, Message struct or custom Tact Struct. Take a look our receivers:

• receive(msg: Add) - specifies actions with messages defined in the beginning by Message add. It will content only one integer number of 32-bits length, that we called amount and nothing else. This receiver invokes function add(amount).
• receive("increment") - specifies actions with messages, that contents comment string "increment" in its body. Here we invoke function add(v) with v = 1, so we increment contract's counter by one.

Declare getter

Last function we need to specifier is get function counter, that will return value of current counter value from contract. Now our contract is ready, we need compile this, so run:

 
contract SampleTactContract with Deployable {
    //previous code
 
    get fun counter(): Int {
      return self.counter;
    }
 

Build contract

Command yarn build will compile contract.tact and place result in tact-template/src/output.

Run yarn command from terminal:

yarn build