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

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        self.reply("Hello, World!".asComment()); // asComment converts a String to a Cell with a comment
    }
}

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How to send a simple message

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        send(SendParameters{
            bounce: true, // default
            to: sender(), // or another destination address
            value: ton("0.01"), // attached amount of Tons to send
            body: "Hello from Tact!".asComment(), // comment (optional)
        });
    }
}

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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.

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        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)
        });
    }
}

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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.

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        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)
        });
    }
}

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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

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        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)
        });
    }
}

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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.

import "@stdlib/deploy";
contract Example with Deployable {
    receive() {
        let comment: StringBuilder = beginComment();
        let longString = "..."; // Some string with more than 127 characters.
        comment.append(longString);

        send(SendParameters{
            // bounce = true by default
            to: sender(),
            value: 0,
            mode: SendIgnoreErrors,
            body: comment.toCell(),
        });
    }
}

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