Single-contract Communication

This page lists examples of communication of a single deployed contract with other contracts on blockchain.

For examples of communication between multiple deployed contracts see: Multi-contract communication.

How to make a basic reply

receive() {
    self.reply("Hello, World!".asComment()); // asComment converts a String to a Cell with a comment
}

How to send a simple message

send(SendParameters{
    bounce: true, // default
    to: destinationAddress,
    value: ton("0.01"), // attached amount of Tons to send
    body: "Hello from Tact!".asComment() // comment (optional)
});

How to send a message with the entire balance

If we need to send the whole balance of the smart contract, then we should use the SendRemainingBalance send mode. Alternatively, we can use mode: 128, which has the same meaning.

send(SendParameters{
    // bounce = true by default
    to: sender(), // send the message back to the original sender
    value: 0,
    mode: SendRemainingBalance, // or mode: 128
    body: "Hello from Tact!".asComment() // comment (optional)
});

How to send a message with the remaining value

If we want to make a reply to the same sender, we can use the mode SendRemainingValue (i.e. mode: 64), which carries all the remaining value of the inbound message in addition to the value initially indicated in the new message.

send(SendParameters{
    // bounce = true by default
    to: sender(), // send the message back to the original sender
    value: 0,
    mode: SendRemainingValue,
    body: "Hello from Tact!".asComment() // comment (optional)
});

It's often useful to add the SendIgnoreErrors flag too, in order to ignore any errors arising while processing this message during the action phaseL

send(SendParameters{
    // bounce = true by default
    to: sender(), // send the message back to the original sender
    value: 0,
    mode: SendRemainingValue | SendIgnoreErrors, // prefer using | over + for the mode
    body: "Hello from Tact!".asComment()         // comment (optional)
});

The latter example is identical to using a .reply() function.

How to send a message with a long text comment

If we need to send a message with a lengthy text comment, we should create a String that consists of more than $127$ characters. To do this, we can utilize the StringBuilder primitive type and its methods called beginComment() and append(). Prior to sending, we should convert this string into a cell using the toCell() method.

let comment: StringBuilder = beginComment();
let longString = "..."; // Some string with more than 127 characters.
str_builder.append(longString);
 
send(SendParameters{
    // bounce = true by default
    to: sender(),
    value: 0,
    mode: SendIgnoreErrors,
    body: longString.toCell(),
});

💡

Useful links:
"Sending messages" in the Book
"Message mode" in the Book StringBuilder in the Book
Cell in Language→Reference

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Overview Type conversion