Expressions

Every operator in Tact forms an expression, but there’s much more to uncover, as Tact offers a wide range of expressive options to choose from.

The current maximum allowed nesting level of expressions is 83. An attempt to write a deeper expression will result in a compilation error:

fun elegantWeaponsForCivilizedAge(): Int {
    return
    ((((((((((((((((((((((((((((((((
        ((((((((((((((((((((((((((((((((
            (((((((((((((((((((( // 84 parens, compilation error!
                42
            ))))))))))))))))))))
        ))))))))))))))))))))))))))))))))
    ))))))))))))))))))))))))))))))));
}

Literals

Literals represent values in Tact. These are fixed values—not variables—that you literally provide in your code. All literals in Tact are expressions themselves.

You can also call extension functions defined on certain primitive types directly on their corresponding literal values:

// Calling toString() defined for Int on an integer literal:
42.toString();

// Calling asComment() defined for String on a string literal:
"Tact is awesome!".asComment();

Integer literals

Integer literals can be written in decimal (base $10$ ), hexadecimal (base $16$ ), octal (base $8$ ), and binary (base $2$ ) notations:

A decimal integer literal is a sequence of digits ( $\mathrm{0 - 9}$ ).
A leading $\mathrm{0x}$ (or $\mathrm{0X}$ ) indicates a hexadecimal integer literal. They can include digits ( $\mathrm{0 - 9}$ ) and the letters $\mathrm{a - f}$ and $\mathrm{A - F}$ . Note that the case of a character does not change its value. Therefore, $\mathrm{0xa}$ = $\mathrm{0xA}$ = 10 and $\mathrm{0xf}$ = $\mathrm{0xF}$ = 15.
A leading $\mathrm{0o}$ (or $\mathrm{0O}$ ) indicates an octal integer literal. They can include only the digits $\mathrm{0 - 7}$ .
A leading $\mathrm{0b}$ (or $\mathrm{0B}$ ) indicates a binary integer literal. They can include only the digits $0$ and $1$ .

Some examples of integer literals:

// decimal, base 10:
0, 42, 1_000, 020

// hexadecimal, base 16:
0xABC, 0xF, 0x0011

// octal, base 8:
0o777, 0o001

// binary, base 2:
0b01111001_01101111_01110101_00100000_01100001_01110010_01100101_00100000_01100001_01110111_01100101_01110011_01101111_01101101_01100101

Read more about integers and the Int type on the dedicated page: Integers.

Boolean literals

The Bool type has only two literal values: true and false.

true == true;
true != false;

Read more about booleans and the Bool type in the dedicated chapter: Booleans.

String literals

A string literal is zero or more characters enclosed in double (") quotation marks. All string literals are objects of the String type.

"foo";
"1234";

Tact strings support a range of escape sequences starting with a backslash \\ character:

\\ — literal backslash
\" — double quote
\n — newline
\r — carriage return
\t — tab
\v — vertical tab
\b — backspace
\f — form feed
\x00 through \xFF — code point, must be exactly two hex digits long
\u0000 through \uFFFF — Unicode code point, must be exactly four hex digits long
\u{0} through \u{10FFFF} — Unicode code point, can be from 1 to 6 hex digits long

// \\
"escape \\ if \\ you \\ can \\";

// \"
"this \"literally\" works";

// \n
"line \n another line";

// \r
"Shutters \r Like \r This \r One";

// \t
"spacing \t granted!";

// \v
"those \v words \v are \v aligned";

// \b
"rm\b\bcreate!";

// \f
"form \f feed";

// \x00 - \xFF
"this \x22literally\x22 works"; // \x22 represents a double quote

// \u0000 - \uFFFF
"danger, \u26A1 high voltage \u26A1"; // \u26A1 represents the ⚡ emoji

// \u{0} - \u{10FFFF}
"\u{1F602} LOL \u{1F602}"; // \u{1F602} represents the 😂 emoji

// This Unicode code point is outside of valid range 000000–10FFFF
"\u{FFFFFF}"; // COMPILATION ERROR!

`null` literal

The null value is written with a null literal. It is not an identifier and does not refer to any object. It is also not an instance of a primitive type. Instead, null represents a lack of identification and the intentional absence of any value.

let var: Int? = null; // variable which can hold a null value
var = 42;
if (var != null) {
    var!! + var!!;
}

Read more about working with null on the dedicated page: Optionals.

Identifiers

An identifier is a sequence of characters in the code that identifies a variable, constant, map, a function, as well as a Struct, Message, contract, trait, or their fields and methods. Identifiers are case-sensitive and not quoted.

In Tact, identifiers may contain Latin lowercase letters a-z, Latin uppercase letters A-Z, underscores _, and digits $\mathrm{0 - 9}$ , but may not start with a digit. No other symbols are allowed, and Unicode identifiers are prohibited.

Note that identifiers for primitive types start with an uppercase letter. User-defined composite types, such as Structs and Messages, must also be capitalized.

Instantiation

You can create instances of the following types:

struct StExample {
    fieldInit: Int = 1;
    fieldUninit: Int;
}

fun example() {
    // Instance with default value of fieldInit
    StExample{ fieldUninit: 2 };

    // Instance with both fields set
    StExample{
        fieldInit: 0,
        fieldUninit: 2, // trailing comma is allowed
    };
}

Field access

You can directly access fields of the following types:

struct StExample {
    fieldInit: Int = 1;
    fieldUninit: Int;
}

fun example(): Int {
    let struct: StExample = StExample{ fieldUninit: 2 }; // instantiation

    struct.fieldInit;          // access a field
    return struct.fieldUninit; // return field value from the function
}

Extension function call

Extension functions are defined only on specific types. They can be called similarly to method calls in many other languages:

42.toString(); // toString() is a stdlib function that is defined on Int type

Static function call

A global static function or an internal function of a contract can be called from anywhere in the function body:

contract ExampleContract {
    receive() {
        now(); // now() is a static function of stdlib
        let expiration: Int = now() + 1000; // operation and variable declaration
        expiration = self.answerQuestion(); // internal function
    }
    fun answerQuestion(): Int {
        return 42;
    }
}

`initOf`

Gas-expensive

The expression initOf computes the initial state, i.e., StateInit, of a contract:

//                     argument values of contract or init() parameters
//                     ↓   ↓
initOf ExampleContract(42, 100); // returns a Struct StateInit{}
//     ---------------
//     ↑
//     name of the contract
//     ↓
//     ---------------
initOf ExampleContract(
    42,  // first argument
    100, // second argument; a trailing comma is allowed
);

The StateInit is a struct consisting of the following fields:

Field	Type	Description
`code`	`Cell`	The initial code of the contract (compiled bitcode)
`data`	`Cell`	The initial data of the contract (parameters of the `init()` function or contract parameters)

For workchain 0, the Address of the current contract obtained by calling the myAddress() function is identical to the one that can be obtained by calling the contractAddress() function with the initial state of the current contract computed via initOf:

contract TheKingPrawn {
    receive("keeping the address") {
        let myAddr1 = myAddress();
        let myAddr2 = contractAddress(initOf TheKingPrawn());

        myAddr1 == myAddr2; // true
    }
}

However, if you only need the address of the current contract at runtime and not its StateInit, use the myAddress() function, as it consumes significantly less gas.

`codeOf`

Gas-expensive Available since Tact 1.6

The expression codeOf returns a Cell containing the code of a contract:

codeOf ExampleContract; // a Cell with ExampleContract code
//     ---------------
//     ↑
//     name of the contract

If codeOf is used for the current contract, its result is equivalent to calling myCode().

contract ExampleContract() {
    receive() {
        myCode() == codeOf ExampleContract; // true
    }
}

If you only need the code of a given contract and not its StateInit, prefer using codeOf ContractName over initOf ContractName(param1, param2, ...) to significantly reduce gas usage.