Base trait

Every contract in Tact implicitly inherits the BaseTrait trait, which contains a number of the most useful internal functions for any kind of contract, and a constant self.storageReserve aimed at advanced users of Tact.

Tip

Prior to 1.6.0, BaseTrait was also implicitly inherited by traits, but now you must explicitly specify with BaseTrait for your traits to use it.

Constants

self.storageReserve

virtual const storageReserve: Int = 0;

Usage example:

contract AllYourStorageBelongsToUs {
    // This would change the behavior of self.forward() function,
    // causing it to try reserving this amount of nanoToncoins before
    // forwarding a message with SendRemainingBalance mode
    override const storageReserve: Int = ton("0.1");
}

Functions

self.reply

virtual fun reply(body: Cell?);

An alias to calling the self.forward() function with the following arguments:

self.forward(sender(), body, true, null);
//           ↑         ↑     ↑     ↑
//           |         |     |     init: StateInit?
//           |         |     bounce: Bool
//           |         body: Cell?
//           to: Address

Usage example:

// This message can bounce back to us!
self.reply("Beware, this is my reply to you!".asComment());

self.notify

virtual fun notify(body: Cell?);

An alias to calling the self.forward() function with the following arguments:

self.forward(sender(), body, false, null);
//           ↑         ↑     ↑      ↑
//           |         |     |      init: StateInit?
//           |         |     bounce: Bool
//           |         body: Cell?
//           to: Address

Usage example:

// This message won't bounce!
self.notify("Beware, this is my reply to you!".asComment());

self.forward

virtual fun forward(to: Address, body: Cell?, bounce: Bool, init: StateInit?);

Queues the message (bounceable or non-bounceable) to be sent to the specified address to. Optionally, you may provide a body of the message and the init package.

When self.storageReserve constant is overwritten to be greater than $0$, before sending a message it also tries to reserve the self.storageReserve amount of nanoToncoins from the remaining balance before making the send in the SendRemainingBalance ($128$) mode.

In case reservation attempt fails and in the default case without the attempt, the message is sent with the SendRemainingValue ($64$) mode instead.

Note

Note, that self.forward() never sends additional nanoToncoins on top of what’s available on the balance.
To be able to send more nanoToncoins with a single message, use the send() function.

Usage example:

import "@stdlib/ownable";

message PayoutOk {
    address: Address;
    value: Int as coins;
}

contract Payout with Ownable {
    completed: Bool;
    owner: Address;

    init(owner: Address) {
        self.owner = owner;
        self.completed = false;
    }

    // ... some actions there ...

    // Bounced receiver function, which is called when the specified outgoing message bounces back
    bounced(msg: bounced<PayoutOk>) {
        // Reset completed flag if our message bounced
        self.completed = false;

        // Send a notification that the payout failed using the remaining funds for processing this send
        self.forward(self.owner, "Payout failed".asComment(), false, null);
    }
}