Glossary
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.
_10let a: String = "hello"_10let 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.
_10let a: String = "hello"_10let 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. &&):
_10let a = true_10let b = false_10_10let 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.
_16// Declare a resource named `SomeResource`_16access(all) resource SomeResource {_16 access(all) var value: Int_16_16 init(value: Int) {_16 self.value = value_16 }_16}_16_16// we use the '@' symbol to reference a resource type_16let a: @SomeResource <- create SomeResource(value: 0)_16_16// also in functions declarations_16access(all) fun use(resource: @SomeResource) {_16 destroy resource_16}
: (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.
_10let a: Bool = true // declares variable `a` with type `Bool`_10_10// or_10_10fun 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:
_10let 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
_10let a = 1 // declares a variable `a` with value `1`
Assignment
_10a = 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.
_10let a: Bool = true_10let 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.
_10let a: Int? = nil_10let b: Int? = 3_10_10let c: Int = a! // panics, because = nil_10let 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.
_10let result = 4 / 2
Path separator
In a path, the forward slash separates the domain, storage or public, and the identifier.
_10let storagePath = /storage/path_10storagePath.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.
_10resource R {}_10_10let 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.
_10access(all) resource R {}_10_10var a: @R? <- nil_10a <-! 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//_10let 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:
_10let 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//_15let 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//_15let 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//_15let c = 1 ?? 2
_ (underscore)
The _ (underscore) symbol has several uses.
Names
The _ (underscore) can be used in names, e.g. in variables and types.
_10let _a = true // used as a variable name_10let another_one = false
Number Literals
The _ (underscore) can also be used to split up numerical components.
_10let 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_10fun double(_ x: Int): Int {_10 return x * 2_10}_10_10let result = double(4)