Message mode

As it was previously mentioned, messages are sent with the mode param of a struct SendParameters. It’s an Int value, which is combined from base modes and optional flags, which are also Int values.

It’s possible to use raw Int values and manually provide them for the mode, but for your convenience there’s a set of constants which you may use to construct the compound mode with ease. Take a look at the following tables for more information on base modes and optional flags.

Base modes

Mode value	Constant name	Description
$0$	Since Tact 1.6 `SendDefaultMode`	Ordinary message (default).
$64$	`SendRemainingValue`	Carry all the remaining value of the inbound message in addition to the value initially indicated in the new message.
$128$	`SendRemainingBalance`	Carry all the remaining balance of the current smart contract instead of the value originally indicated in the message.

Optional flags

Flag value	Constant name	Description
$+1$	`SendPayGasSeparately`	Pay forward fees separately from the message value.
$+2$	`SendIgnoreErrors`	Ignore any errors arising while processing this message during the action phase.
$+16$	`SendBounceIfActionFail`	Bounce transaction in case of any errors during action phase. Has no effect if flag $+2$ , `SendIgnoreErrors` is used.
$+32$	`SendDestroyIfZero`	Current account must be destroyed if its resulting balance is zero (often used with mode $128$ , `SendRemainingBalance`).

Combining modes with flags

To make the Int value for mode field of SendParameters, you just have to combine base modes with optional flags by applying the bitwise OR operation.

For example, if you want to send a regular message and pay transfer fees separately, use the mode $0$ (default) and a flag $+1$ to get mode $= 1$ , which is equal to using SendPayGasSeparately constant.

Alternatively, if you want to send the whole contract balance and destroy it immediately, use the mode $128$ and flag $+32$ to get mode $= 160$ , which is equal to SendRemainingBalance | SendDestroyIfZero.

Here’s how the latter example would look in code:

let to: Address = address("...");
let value: Int = ton("1");
send(SendParameters{
    to: to,
    value: value,
    mode: SendRemainingBalance | SendDestroyIfZero,
    body: "Hello, World!".asComment(),
});