Glossary

tip

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.

_10

let a: String = "hello"

_10

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.

_10

let a: String = "hello"

_10

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. &&):

_10

let a = true

_10

let b = false

_10

_10

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.

_20

// Declare a resource named `SomeResource`

_20

access(all)

_20

resource SomeResource {

_20

_20

access(all)

_20

var value: Int

_20

_20

init(value: Int) {

_20

self.value = value

_20

}

_20

}

_20

_20

// we use the '@' symbol to reference a resource type

_20

let a: @SomeResource <- create SomeResource(value: 0)

_20

_20

// also in functions declarations

_20

access(all)

_20

fun use(resource: @SomeResource) {

_20

destroy resource

_20

}

: (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.

_10

let a: Bool = true // declares variable `a` with type `Bool`

_10

_10

// or

_10

_10

fun addOne(x: Int): Int { // return type of Int

_10

return x + 1

_10

}

Ternary Conditional Operator

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

_10

let a = 1 > 2 ? 3 : 4

_10

// should be read as:

_10

// "is 1 greater than 2?"

_10

// "if YES, then set a = 3,

_10

// "otherwise, set a = 4.

= (equals)

The = (equals) symbol has several uses.

Variable Declaration

_10

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

Assignment

_10

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.

_10

let a: Bool = true

_10

let b: Bool = !a

_10

_10

// 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.

_10

let a: Int? = nil

_10

let b: Int? = 3

_10

_10

let c: Int = a! // panics, because = nil

_10

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.

_10

let result = 4 / 2

Path separator

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

_10

let storagePath = /storage/path

_10

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.

_10

resource R {}

_10

_10

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.

_10

access(all)

_10

resource R {}

_10

_10

var a: @R? <- nil

_10

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.

_10

// Declare a constant which has an optional integer type

_10

//

_10

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:

_10

let a = 1 > 2 ? 3 : 4

_10

// should be read as:

_10

// "is 1 greater than 2?"

_10

// "if YES, then set a = 3,

_10

// "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.

_15

// Declare a constant which has an optional integer type

_15

//

_15

let a: Int? = nil

_15

_15

// Declare a constant with a non-optional integer type,

_15

// which is initialized to `a` if it is non-nil, or 42 otherwise.

_15

//

_15

let b: Int = a ?? 42

_15

// `b` is 42, as `a` is nil

_15

_15

_15

// Invalid: nil-coalescing operator is applied to a value which has a non-optional type

_15

// (the integer literal is of type `Int`).

_15

//

_15

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.

_10

let _a = true // used as a variable name

_10

let another_one = false

Number Literals

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

_10

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.

_10

// The special argument label _ is specified for the parameter,

_10

// so no argument label has to be provided in a function call.

_10

_10

fun double(_ x: Int): Int {

_10

return x * 2

_10

}

_10

_10

let result = double(4)