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Glossary

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& (ampersand)​

The & (ampersand) symbol has several uses.

Reference​

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


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let a: String = "hello"
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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, i.e. the full syntax is auth &T, whereas unauthorized references do not have a modifier.


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

Logical Operator​

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


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let a = true
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let b = false
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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.


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

: (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.


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

Ternary Conditional Operator​

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


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

= (equals)​

The = (equals) symbol has several uses.

Variable Declaration​


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

Assignment​


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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.


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let a: Bool = true
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let b: Bool = !a
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// 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.


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let a: Int? = nil
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let b: Int? = 3
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let c: Int = a! // panics, because = nil
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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.


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let result = 4 / 2

Path separator​

In a Path, the forward slash separates the domain (e.g. storage, private, public) and the identifier.


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let storagePath = /storage/path
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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.

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resource R {}
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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.


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pub resource R {}
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var a: @R? <- nil
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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.


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// Declare a constant which has an optional integer type
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//
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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:


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


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


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

Number Literals​

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


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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.


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