Version: Next

Glossary

info

Tip: CTRL/⌘ + F and type in the symbol or operator you want to look up.

`&` (ampersand)

The & (ampersand) symbol has several uses.

Reference

If an expression starts with the & (ampersand) symbol, it creates a reference.

let a: String = "hello"
let refOfA: &String = &a as &String

References may also be authorized if the & symbol is preceded by auth (otherwise the reference is unauthorized).

Authorized references have the auth modifier, along with the set of entitlements to which the reference is authorized, i.e. the full syntax is auth(E, F) &T, whereas unauthorized references do not have a modifier.

let a: String = "hello"
let refOfA: auth(X) &String = &a as auth(X) &String

Logical Operator

It can be also used as a logical operator (AND), by appearing twice in succession (i.e. &&):

let a = true
let b = false
let c = a && b // false

`@` (at)

The @ (at) symbol before a type is used to annotate whether the type is a resource.

The @ symbol must appear at the beginning of the type, not inside. For example, an array of NFTs is @[NFT], not [@NFT]. This emphasizes the whole type acts like a resource.

// Declare a resource named `SomeResource`
access(all) resource SomeResource {
    access(all) var value: Int
    init(value: Int) {
        self.value = value
    }
}
// we use the '@' symbol to reference a resource type
let a: @SomeResource <- create SomeResource(value: 0)
// also in functions declarations
access(all) fun use(resource: @SomeResource) {
    destroy resource
}

`:` (colon)

The : (colon) symbol has several uses.

Type Declaration

If a : (colon) follows a variable/constant/function declaration, it is used to declare its type.

let a: Bool = true // declares variable `a` with type `Bool`
// or
fun addOne(x: Int): Int { // return type of Int
    return x + 1
}

Ternary Conditional Operator

The : (colon) is also be used in ternary operations to represent the "otherwise" section, such as the following:

let a = 1 > 2 ? 3 : 4
// should be read as:
//   "is 1 greater than 2?"
//   "if YES, then set a = 3,
//   "otherwise, set a = 4.

`=` (equals)

The = (equals) symbol has several uses.

Variable Declaration

let a = 1 // declares a variable `a` with value `1`

Assignment

a = 1  // assigns the value `1` to variable `a `

`!` (exclamation mark)

The ! (exclamation mark) symbol has a different effect whether it precedes or succeeds a variable.

When it immediately precedes a boolean-type variable, it negates it.

let a: Bool = true
let b: Bool = !a
// b is false

When it immediately succeeds an optional variable, it force-unwraps it. Force-unwrapping returns the value inside an optional if it contains a value, or panics and aborts the execution if the optional has no value, i.e. the optional value is nil.

let a: Int? = nil
let b: Int? = 3
let c: Int = a! // panics, because = nil
let d: Int = b! // initialized correctly as 3

`/` (forward slash)

The / (forward slash) symbol has several uses.

Division Operator

Inbetween two expressions, the forward slash acts as the division operator.

let result = 4 / 2

Path separator

In a path, the forward slash separates the domain, storage or public, and the identifier.

let storagePath = /storage/path
storagePath.toString()  // is "/storage/path"

`<-` (lower than, hyphen) (Move operator)

The move operator <- is like the assignment operator =, but must be used when the value is a resource. To make assignment of resources explicit, the move operator <- must be used when:

The resource is the initial value of a constant or variable,
The resource is moved to a different variable in an assignment,
The resource is moved to a function as an argument
The resource is returned from a function.

resource R {}
let a <- create R() // we instantiate a new resource and move it into a

`<-!` (lower than, hyphen, exclamation mark) (Force-assignment move operator)

The force-assignment move operator <-! moves a resource value to an optional variable. If the variable is nil, the move succeeds. If it is not nil, the program aborts.

access(all) resource R {}
var a: @R? <- nil
a <-! create R()

`<->` (lower than, hyphen, greater than) (Swap operator)

The swapping operator <-> swaps two resource between the variables to the left and right of it.

`+` (plus), `-` (minus), `*` (asterisk), `%` (percentage sign)

These are all typical arithmetic operators:

Addition: +
Subtraction: -
Multiplication: *
Remainder: %

`?` (question mark)

The ? (question mark) symbol has several uses.

Optional

If a ? (question mark) follows a variable/constant, it represents an optional. An optional can either have a value or nothing at all.

// Declare a constant which has an optional integer type
//
let a: Int? = nil

Ternary Conditional Operator

The ? (question mark) is also be used in ternary operations to represent the "then" section, such as the following:

let a = 1 > 2 ? 3 : 4
// should be read as:
//   "is 1 greater than 2?"
//   "if YES, then set a = 3,
//   "otherwise, set a = 4.

Nil-Coalescing Operator

The ? (question mark) is also used in the nil-coalescing operator ??.

It returns the value inside the optional, if the optional contains a value, or returns an alternative value if the optional has no value, i.e., the optional value is nil.

// Declare a constant which has an optional integer type
//
let a: Int? = nil
// Declare a constant with a non-optional integer type,
// which is initialized to `a` if it is non-nil, or 42 otherwise.
//
let b: Int = a ?? 42
// `b` is 42, as `a` is nil
// Invalid: nil-coalescing operator is applied to a value which has a non-optional type
// (the integer literal is of type `Int`).
//
let c = 1 ?? 2

`_` (underscore)

The _ (underscore) symbol has several uses.

Names

The _ (underscore) can be used in names, e.g. in variables and types.

let _a = true // used as a variable name
let another_one = false

Number Literals

The _ (underscore) can also be used to split up numerical components.

let b = 100_000_000 // used to split up a number (supports all number types, e.g. 0b10_11_01)

Argument Labels

The _ (underscore) can also be to indicate that a parameter in a function has no argument label.

// The special argument label _ is specified for the parameter,
// so no argument label has to be provided in a function call.
fun double(_ x: Int): Int {
    return x * 2
}
let result = double(4)

& (ampersand)​

Reference​

Logical Operator​

@ (at)​

: (colon)​

Type Declaration​

Ternary Conditional Operator​

= (equals)​

Variable Declaration​

Assignment​

! (exclamation mark)​

/ (forward slash)​

Division Operator​

Path separator​

<- (lower than, hyphen) (Move operator)​

<-! (lower than, hyphen, exclamation mark) (Force-assignment move operator)​

<-> (lower than, hyphen, greater than) (Swap operator)​

+ (plus), - (minus), * (asterisk), % (percentage sign)​

? (question mark)​

Optional​

Ternary Conditional Operator​

Nil-Coalescing Operator​

_ (underscore)​

Names​

Number Literals​

Argument Labels​

`&` (ampersand)

Reference

Logical Operator

`@` (at)

`:` (colon)

Type Declaration

Ternary Conditional Operator

`=` (equals)

Variable Declaration

Assignment

`!` (exclamation mark)

`/` (forward slash)

Division Operator

Path separator

`<-` (lower than, hyphen) (Move operator)

`<-!` (lower than, hyphen, exclamation mark) (Force-assignment move operator)

`<->` (lower than, hyphen, greater than) (Swap operator)

`+` (plus), `-` (minus), `*` (asterisk), `%` (percentage sign)

`?` (question mark)

Optional

Ternary Conditional Operator

Nil-Coalescing Operator

`_` (underscore)

Names

Number Literals

Argument Labels