Version: Next

# Values and Types

Values are objects, like for example booleans, integers, or arrays. Values are typed.

## Booleans​

The two boolean values true and false have the type Bool.

## Numeric Literals​

Numbers can be written in various bases. Numbers are assumed to be decimal by default. Non-decimal literals have a specific prefix.

Numeral systemPrefixCharacters
DecimalNoneone or more numbers (0 to 9)
Binary0bone or more zeros or ones (0 or 1)
Octal0oone or more numbers in the range 0 to 7
Hexadecimal0xone or more numbers, or characters a to f, lowercase or uppercase
_25// A decimal number_25//_251234567890 // is 1234567890_25_25// A binary number_25//_250b101010 // is 42_25_25// An octal number_25//_250o12345670 // is 2739128_25_25// A hexadecimal number_25//_250x1234567890ABCabc // is 1311768467294898876_25_25// Invalid: unsupported prefix 0z_25//_250z0_25_25// A decimal number with leading zeros. Not an octal number!_2500123 // is 123_25_25// A binary number with several trailing zeros._250b001000 // is 8

Decimal numbers may contain underscores (_) to logically separate components.

_10let largeNumber = 1_000_000_10_10// Invalid: Value is not a number literal, but a variable._10let notNumber = _123

Underscores are allowed for all numeral systems.

_10let binaryNumber = 0b10_11_01

## Integers​

Integers are numbers without a fractional part. They are either signed (positive, zero, or negative) or unsigned (positive or zero).

Signed integer types which check for overflow and underflow have an Int prefix and can represent values in the following ranges:

• Int8: -2^7 through 2^7 − 1 (-128 through 127)
• Int16: -2^15 through 2^15 − 1 (-32768 through 32767)
• Int32: -2^31 through 2^31 − 1 (-2147483648 through 2147483647)
• Int64: -2^63 through 2^63 − 1 (-9223372036854775808 through 9223372036854775807)
• Int128: -2^127 through 2^127 − 1
• Int256: -2^255 through 2^255 − 1

Unsigned integer types which check for overflow and underflow have a UInt prefix and can represent values in the following ranges:

• UInt8: 0 through 2^8 − 1 (255)
• UInt16: 0 through 2^16 − 1 (65535)
• UInt32: 0 through 2^32 − 1 (4294967295)
• UInt64: 0 through 2^64 − 1 (18446744073709551615)
• UInt128: 0 through 2^128 − 1
• UInt256: 0 through 2^256 − 1

Unsigned integer types which do not check for overflow and underflow, i.e. wrap around, have the Word prefix and can represent values in the following ranges:

• Word8: 0 through 2^8 − 1 (255)
• Word16: 0 through 2^16 − 1 (65535)
• Word32: 0 through 2^32 − 1 (4294967295)
• Word64: 0 through 2^64 − 1 (18446744073709551615)
• Word128: 0 through 2^128 − 1 (340282366920938463463374607431768211455)
• Word256: 0 through 2^256 − 1 (115792089237316195423570985008687907853269984665640564039457584007913129639935)

The types are independent types, i.e. not subtypes of each other.

See the section about arithmetic operators for further information about the behavior of the different integer types.

_10// Declare a constant that has type UInt8 and the value 10._10let smallNumber: UInt8 = 10
_10// Invalid: negative literal cannot be used as an unsigned integer_10//_10let invalidNumber: UInt8 = -10

In addition, the arbitrary precision integer type Int is provided.

_10let veryLargeNumber: Int = 10000000000000000000000000000000

Integer literals are inferred to have type Int, or if the literal occurs in a position that expects an explicit type, e.g. in a variable declaration with an explicit type annotation.

_10let someNumber = 123_10_10// someNumber has type Int

Negative integers are encoded in two's complement representation.

Integer types are not converted automatically. Types must be explicitly converted, which can be done by calling the constructor of the type with the integer type.

_15let x: Int8 = 1_15let y: Int16 = 2_15_15// Invalid: the types of the operands, Int8 and Int16 are incompatible._15let z = x + y_15_15// Explicitly convert x from Int8 to Int16._15let a = Int16(x) + y_15_15// a has type Int16_15_15// Invalid: The integer literal is expected to be of type Int8,_15// but the large integer literal does not fit in the range of Int8._15//_15let b = x + 1000000000000000000000000

### Integer Functions​

Integers have multiple built-in functions you can use.

• _10fun toString(): String

Returns the string representation of the integer.

_10let answer = 42_10_10answer.toString() // is "42"
• _10fun toBigEndianBytes(): [UInt8]

Returns the byte array representation ([UInt8]) in big-endian order of the integer.

_10let largeNumber = 1234567890_10_10largeNumber.toBigEndianBytes() // is [73, 150, 2, 210]

All integer types support the following functions:

• _10fun T.fromString(_ input: String): T?

Attempts to parse an integer value from a base-10 encoded string, returning nil if the string is invalid.

For a given integer n of type T, T.fromString(n.toString()) is equivalent to wrapping n up in an optional.

Strings are invalid if:

• they contain non-digit characters
• they don't fit in the target type

For signed integer types like Int64, and Int, the string may optionally begin with + or - sign prefix.

For unsigned integer types like Word64, UInt64, and UInt, sign prefices are not allowed.

Examples:

_10let fortyTwo: Int64? = Int64.fromString("42") // ok_10_10let twenty: UInt? = UInt.fromString("20") // ok_10_10let nilWord: Word8? = Word8.fromString("1024") // nil, out of bounds_10_10let negTwenty: Int? = Int.fromString("-20") // ok
• _10fun T.fromBigEndianBytes(_ bytes: [UInt8]): T?

Attempts to parse an integer value from a byte array representation ([UInt8]) in big-endian order, returning nil if the input bytes are invalid.

For a given integer n of type T, T.fromBigEndianBytes(n.toBigEndianBytes()) is equivalent to wrapping n up in an optional.

The bytes are invalid if:

• length of the bytes array exceeds the number of bytes needed for the target type
• they don't fit in the target type

Examples:

_10let fortyTwo: UInt32? = UInt32.fromBigEndianBytes([42]) // ok_10_10let twenty: UInt? = UInt.fromBigEndianBytes([0, 0, 20]) // ok_10_10let nilWord: Word8? = Word8.fromBigEndianBytes("[0, 22, 0, 0, 0, 0, 0, 0, 0]") // nil, out of bounds_10_10let nilWord2: Word8? = Word8.fromBigEndianBytes("[0, 0]") // nil, size (2) exceeds number of bytes needed for Word8 (1)_10_10let negativeNumber: Int64? = Int64.fromBigEndianBytes([128, 0, 0, 0, 0, 0, 0, 1]) // ok -9223372036854775807

## Fixed-Point Numbers​

info

🚧 Status: Currently only the 64-bit wide Fix64 and UFix64 types are available. More fixed-point number types will be added in a future release.

Fixed-point numbers are useful for representing fractional values. They have a fixed number of digits after decimal point.

They are essentially integers which are scaled by a factor. For example, the value 1.23 can be represented as 1230 with a scaling factor of 1/1000. The scaling factor is the same for all values of the same type and stays the same during calculations.

Fixed-point numbers in Cadence have a scaling factor with a power of 10, instead of a power of 2, i.e. they are decimal, not binary.

Signed fixed-point number types have the prefix Fix, have the following factors, and can represent values in the following ranges:

• Fix64: Factor 1/100,000,000; -92233720368.54775808 through 92233720368.54775807

Unsigned fixed-point number types have the prefix UFix, have the following factors, and can represent values in the following ranges:

• UFix64: Factor 1/100,000,000; 0.0 through 184467440737.09551615

### Fixed-Point Number Functions​

Fixed-Point numbers have multiple built-in functions you can use.

• _10fun toString(): String

Returns the string representation of the fixed-point number.

_10let fix = 1.23_10_10fix.toString() // is "1.23000000"
• _10fun toBigEndianBytes(): [UInt8]

Returns the byte array representation ([UInt8]) in big-endian order of the fixed-point number.

_10let fix = 1.23_10_10fix.toBigEndianBytes() // is [0, 0, 0, 0, 7, 84, 212, 192]

All fixed-point types support the following functions:

• _10fun T.fromString(_ input: String): T?

Attempts to parse a fixed-point value from a base-10 encoded string, returning nil if the string is invalid.

For a given fixed-point numeral n of type T, T.fromString(n.toString()) is equivalent to wrapping n up in an optional.

Strings are invalid if:

• they contain non-digit characters.
• they don't fit in the target type.
• they're missing a decimal or fractional component. For example, both "0." and ".1" are invalid strings, but "0.1" is accepted.

For signed types like Fix64, the string may optionally begin with + or - sign prefix.

For unsigned types like UFix64, sign prefices are not allowed.

Examples:

_11let nil1: UFix64? = UFix64.fromString("0.") // nil, fractional part is required_11_11let nil2: UFix64? = UFix64.fromString(".1") // nil, decimal part is required_11_11let smol: UFix64? = UFix64.fromString("0.1") // ok_11_11let smolString: String = "-0.1"_11_11let nil3: UFix64? = UFix64.fromString(smolString) // nil, unsigned types don't allow a sign prefix_11_11let smolFix64: Fix64? = Fix64.fromString(smolString) // ok
• _10fun T.fromBigEndianBytes(_ bytes: [UInt8]): T?

Attempts to parse an integer value from a byte array representation ([UInt8]) in big-endian order, returning nil if the input bytes are invalid.

For a given integer n of type T, T.fromBigEndianBytes(n.toBigEndianBytes()) is equivalent to wrapping n up in an optional.

The bytes are invalid if:

• length of the bytes array exceeds the number of bytes needed for the target type
• they don't fit in the target type

Examples:

_10let fortyTwo: UFix64? = UFix64.fromBigEndianBytes([0, 0, 0, 0, 250, 86, 234, 0]) // ok, 42.0_10_10let nilWord: UFix64? = UFix64.fromBigEndianBytes("[100, 22, 0, 0, 0, 0, 0, 0, 0]") // nil, out of bounds_10_10let nilWord2: Fix64? = Fix64.fromBigEndianBytes("[0, 22, 0, 0, 0, 0, 0, 0, 0]") // // nil, size (9) exceeds number of bytes needed for Fix64 (8)_10_10let negativeNumber: Fix64? = Fix64.fromBigEndianBytes([255, 255, 255, 255, 250, 10, 31, 0]) // ok, -1

## Minimum and maximum values​

The minimum and maximum values for all integer and fixed-point number types are available through the fields min and max.

For example:

_10let max = UInt8.max_10// max is 255, the maximum value of the type UInt8
_10let max = UFix64.max_10// max is 184467440737.09551615, the maximum value of the type UFix64

## Saturation Arithmetic​

Integers and fixed-point numbers support saturation arithmetic: Arithmetic operations, such as addition or multiplications, are saturating at the numeric bounds instead of overflowing.

If the result of an operation is greater than the maximum value of the operands' type, the maximum is returned. If the result is lower than the minimum of the operands' type, the minimum is returned.

Saturating addition, subtraction, multiplication, and division are provided as functions with the prefix saturating:

• Int8, Int16, Int32, Int64, Int128, Int256, Fix64:

• saturatingAdd
• saturatingSubtract
• saturatingMultiply
• saturatingDivide
• Int:

• none
• UInt8, UInt16, UInt32, UInt64, UInt128, UInt256, UFix64:

• saturatingAdd
• saturatingSubtract
• saturatingMultiply
• UInt:

• saturatingSubtract
_10let a: UInt8 = 200_10let b: UInt8 = 100_10let result = a.saturatingAdd(b)_10// result is 255, the maximum value of the type UInt8

## Floating-Point Numbers​

There is no support for floating point numbers.

Smart Contracts are not intended to work with values with error margins and therefore floating point arithmetic is not appropriate here.

Instead, consider using fixed point numbers.

The type Address represents an address. Addresses are unsigned integers with a size of 64 bits (8 bytes). Hexadecimal integer literals can be used to create address values.

_13// Declare a constant that has type Address._13//_13let someAddress: Address = 0x436164656E636521_13_13// Invalid: Initial value is not compatible with type Address,_13// it is not a number._13//_13let notAnAddress: Address = ""_13_13// Invalid: Initial value is not compatible with type Address._13// The integer literal is valid, however, it is larger than 64 bits._13//_13let alsoNotAnAddress: Address = 0x436164656E63652146757265766572

Integer literals are not inferred to be an address.

_10// Declare a number. Even though it happens to be a valid address,_10// it is not inferred as it._10//_10let aNumber = 0x436164656E636521_10_10// aNumber has type Int

Address can also be created using a byte array or string.

_17// Declare an address with hex representation as 0x436164656E636521._17let someAddress: Address = Address.fromBytes([67, 97, 100, 101, 110, 99, 101, 33])_17_17// Invalid: Provided value is not compatible with type Address. The function panics._17let invalidAddress: Address = Address.fromBytes([12, 34, 56, 11, 22, 33, 44, 55, 66, 77, 88, 99, 111])_17_17// Declare an address with the string representation as "0x436164656E636521"._17let addressFromString: Address? = Address.fromString("0x436164656E636521")_17_17// Invalid: Provided value does not have the "0x" prefix. Returns Nil_17let addressFromStringWithoutPrefix: Address? = Address.fromString("436164656E636521")_17_17// Invalid: Provided value is an invalid hex string. Return Nil._17let invalidAddressForInvalidHex: Address? = Address.fromString("0xZZZ")_17_17// Invalid: Provided value is larger than 64 bits. Return Nil._17let invalidAddressForOverflow: Address? = Address.fromString("0x436164656E63652146757265766572")

Addresses have multiple built-in functions you can use.

• _10fun toString(): String

Returns the string representation of the address. The result has a 0x prefix and is zero-padded.

_10let someAddress: Address = 0x436164656E636521_10someAddress.toString() // is "0x436164656E636521"_10_10let shortAddress: Address = 0x1_10shortAddress.toString() // is "0x0000000000000001"
• _10fun toBytes(): [UInt8]

Returns the byte array representation ([UInt8]) of the address.

_10let someAddress: Address = 0x436164656E636521_10_10someAddress.toBytes() // is [67, 97, 100, 101, 110, 99, 101, 33]

## AnyStruct and AnyResource​

AnyStruct is the top type of all non-resource types, i.e., all non-resource types are a subtype of it.

AnyResource is the top type of all resource types.

_37// Declare a variable that has the type AnyStruct._37// Any non-resource typed value can be assigned to it, for example an integer,_37// but not resource-typed values._37//_37var someStruct: AnyStruct = 1_37_37// Assign a value with a different non-resource type, Bool._37someStruct = true_37_37// Declare a structure named TestStruct, create an instance of it,_37// and assign it to the AnyStruct-typed variable_37//_37struct TestStruct {}_37_37let testStruct = TestStruct()_37_37someStruct = testStruct_37_37// Declare a resource named TestResource_37_37resource TestResource {}_37_37// Declare a variable that has the type AnyResource._37// Any resource-typed value can be assigned to it,_37// but not non-resource typed values._37//_37var someResource: @AnyResource <- create TestResource()_37_37// Invalid: Resource-typed values can not be assigned_37// to AnyStruct-typed variables_37//_37someStruct <- create TestResource()_37_37// Invalid: Non-resource typed values can not be assigned_37// to AnyResource-typed variables_37//_37someResource = 1

However, using AnyStruct and AnyResource does not opt-out of type checking. It is invalid to access fields and call functions on these types, as they have no fields and functions.

_10// Declare a variable that has the type AnyStruct._10// The initial value is an integer,_10// but the variable still has the explicit type AnyStruct._10//_10let a: AnyStruct = 1_10_10// Invalid: Operator cannot be used for an AnyStruct value (a, left-hand side)_10// and an Int value (2, right-hand side)._10//_10a + 2

AnyStruct and AnyResource may be used like other types, for example, they may be the element type of arrays or be the element type of an optional type.

_13// Declare a variable that has the type [AnyStruct],_13// i.e. an array of elements of any non-resource type._13//_13let anyValues: [AnyStruct] = [1, "2", true]_13_13// Declare a variable that has the type AnyStruct?,_13// i.e. an optional type of any non-resource type._13//_13var maybeSomething: AnyStruct? = 42_13_13maybeSomething = "twenty-four"_13_13maybeSomething = nil

AnyStruct is also the super-type of all non-resource optional types, and AnyResource is the super-type of all resource optional types.

_10let maybeInt: Int? = 1_10let anything: AnyStruct = maybeInt

Conditional downcasting allows coercing a value which has the type AnyStruct or AnyResource back to its original type.

## Optionals​

Optionals are values which can represent the absence of a value. Optionals have two cases: either there is a value, or there is nothing.

An optional type is declared using the ? suffix for another type. For example, Int is a non-optional integer, and Int? is an optional integer, i.e. either nothing, or an integer.

The value representing nothing is nil.

_17// Declare a constant which has an optional integer type,_17// with nil as its initial value._17//_17let a: Int? = nil_17_17// Declare a constant which has an optional integer type,_17// with 42 as its initial value._17//_17let b: Int? = 42_17_17// Invalid: b has type Int?, which does not support arithmetic._17b + 23_17_17// Invalid: Declare a constant with a non-optional integer type Int,_17// but the initial value is nil, which in this context has type Int?._17//_17let x: Int = nil

Optionals can be created for any value, not just for literals.

_15// Declare a constant which has a non-optional integer type,_15// with 1 as its initial value._15//_15let x = 1_15_15// Declare a constant which has an optional integer type._15// An optional with the value of x is created._15//_15let y: Int? = x_15_15// Declare a variable which has an optional any type, i.e. the variable_15// may be nil, or any other value._15// An optional with the value of x is created._15//_15var z: AnyStruct? = x

A non-optional type is a subtype of its optional type.

_10var a: Int? = nil_10let b = 2_10a = b_10_10// a is 2

Optional types may be contained in other types, for example arrays or even optionals.

_10// Declare a constant which has an array type of optional integers._10let xs: [Int?] = [1, nil, 2, nil]_10_10// Declare a constant which has a double optional type._10//_10let doubleOptional: Int?? = nil

See the optional operators section for information on how to work with optionals.

## Never​

Never is the bottom type, i.e., it is a subtype of all types. There is no value that has type Never. Never can be used as the return type for functions that never return normally. For example, it is the return type of the function panic.

_17// Declare a function named crashAndBurn which will never return,_17// because it calls the function named panic, which never returns._17//_17fun crashAndBurn(): Never {_17 panic("An unrecoverable error occurred")_17}_17_17// Invalid: Declare a constant with a Never type, but the initial value is an integer._17//_17let x: Never = 1_17_17// Invalid: Declare a function which returns an invalid return value nil,_17// which is not a value of type Never._17//_17fun returnNever(): Never {_17 return nil_17}

## Strings and Characters​

Strings are collections of characters. Strings have the type String, and characters have the type Character. Strings can be used to work with text in a Unicode-compliant way. Strings are immutable.

String and character literals are enclosed in double quotation marks (").

_10let someString = "Hello, world!"

String literals may contain escape sequences. An escape sequence starts with a backslash (\):

• \0: Null character
• \\: Backslash
• \t: Horizontal tab
• \n: Line feed
• \r: Carriage return
• \": Double quotation mark
• \': Single quotation mark
• \u: A Unicode scalar value, written as \u{x}, where x is a 1–8 digit hexadecimal number which needs to be a valid Unicode scalar value, i.e., in the range 0 to 0xD7FF and 0xE000 to 0x10FFFF inclusive
_10// Declare a constant which contains two lines of text_10// (separated by the line feed character \n), and ends_10// with a thumbs up emoji, which has code point U+1F44D (0x1F44D)._10//_10let thumbsUpText =_10 "This is the first line.\nThis is the second line with an emoji: \u{1F44D}"

The type Character represents a single, human-readable character. Characters are extended grapheme clusters, which consist of one or more Unicode scalars.

For example, the single character ü can be represented in several ways in Unicode. First, it can be represented by a single Unicode scalar value ü ("LATIN SMALL LETTER U WITH DIAERESIS", code point U+00FC). Second, the same single character can be represented by two Unicode scalar values: u ("LATIN SMALL LETTER U", code point U+0075), and "COMBINING DIAERESIS" (code point U+0308). The combining Unicode scalar value is applied to the scalar before it, which turns a u into a ü.

Still, both variants represent the same human-readable character ü.

_10let singleScalar: Character = "\u{FC}"_10// singleScalar is ü_10let twoScalars: Character = "\u{75}\u{308}"_10// twoScalars is ü

Another example where multiple Unicode scalar values are rendered as a single, human-readable character is a flag emoji. These emojis consist of two "REGIONAL INDICATOR SYMBOL LETTER" Unicode scalar values.

_10// Declare a constant for a string with a single character, the emoji_10// for the Canadian flag, which consists of two Unicode scalar values:_10// - REGIONAL INDICATOR SYMBOL LETTER C (U+1F1E8)_10// - REGIONAL INDICATOR SYMBOL LETTER A (U+1F1E6)_10//_10let canadianFlag: Character = "\u{1F1E8}\u{1F1E6}"_10// canadianFlag is 🇨🇦

### String Fields and Functions​

Strings have multiple built-in functions you can use:

• _10let length: Int

Returns the number of characters in the string as an integer.

_10let example = "hello"_10_10// Find the number of elements of the string._10let length = example.length_10// length is 5
• _10let utf8: [UInt8]

The byte array of the UTF-8 encoding

_10let flowers = "Flowers \u{1F490}"_10let bytes = flowers.utf8_10// bytes is [70, 108, 111, 119, 101, 114, 115, 32, 240, 159, 146, 144]
• _10fun concat(_ other: String): String

Concatenates the string other to the end of the original string, but does not modify the original string. This function creates a new string whose length is the sum of the lengths of the string the function is called on and the string given as a parameter.

_10let example = "hello"_10let new = "world"_10_10// Concatenate the new string onto the example string and return the new string._10let helloWorld = example.concat(new)_10// helloWorld is now "helloworld"
• _10fun slice(from: Int, upTo: Int): String

Returns a string slice of the characters in the given string from start index from up to, but not including, the end index upTo. This function creates a new string whose length is upTo - from. It does not modify the original string. If either of the parameters are out of the bounds of the string, or the indices are invalid (from > upTo), then the function will fail.

_11let example = "helloworld"_11_11// Create a new slice of part of the original string._11let slice = example.slice(from: 3, upTo: 6)_11// slice is now "low"_11_11// Run-time error: Out of bounds index, the program aborts._11let outOfBounds = example.slice(from: 2, upTo: 10)_11_11// Run-time error: Invalid indices, the program aborts._11let invalidIndices = example.slice(from: 2, upTo: 1)
• _10fun decodeHex(): [UInt8]

Returns an array containing the bytes represented by the given hexadecimal string.

The given string must only contain hexadecimal characters and must have an even length. If the string is malformed, the program aborts

_10let example = "436164656e636521"_10_10example.decodeHex() // is [67, 97, 100, 101, 110, 99, 101, 33]
• _10fun toLower(): String

Returns a string where all upper case letters are replaced with lowercase characters

_10let example = "Flowers"_10_10example.toLower() // is flowers

The String type also provides the following functions:

• _10fun String.encodeHex(_ data: [UInt8]): String

Returns a hexadecimal string for the given byte array

_10let data = [1 as UInt8, 2, 3, 0xCA, 0xDE]_10_10String.encodeHex(data) // is "010203cade"

Strings are also indexable, returning a Character value.

_10let str = "abc"_10let c = str[0] // is the Character "a"
• _10fun String.fromUTF8(_ input: [UInt8]): String?

Attempts to convert a UTF-8 encoded byte array into a String. This function returns nil if the byte array contains invalid UTF-8, such as incomplete codepoint sequences or undefined graphemes.

For a given string s, String.fromUTF8(s.utf8) is equivalent to wrapping s up in an optional.

### Character Fields and Functions​

Character values can be converted into String values using the toString function:

• _10fun toString(): String

Returns the string representation of the character.

_10let c: Character = "x"_10_10c.toString() // is "x"
• _10fun String.fromCharacters(_ characters: [Character]): String

Builds a new String value from an array of Characters. Because Strings are immutable, this operation makes a copy of the input array.

_10let rawUwU: [Character] = ["U", "w", "U"]_10let uwu: String = String.fromCharacters(rawUwU) // "UwU"
• _10let utf8: [UInt8]

The byte array of the UTF-8 encoding

_10let a: Character = "a"_10let a_bytes = a.utf8 // a_bytes is [97]_10_10let bouquet: Character = "\u{1F490}"_10let bouquet_bytes = bouquet.utf8 // bouquet_bytes is [240, 159, 146, 144]

## Arrays​

Arrays are mutable, ordered collections of values. Arrays may contain a value multiple times. Array literals start with an opening square bracket [ and end with a closing square bracket ].

_10// An empty array_10//_10[]_10_10// An array with integers_10//_10[1, 2, 3]

### Array Types​

Arrays either have a fixed size or are variably sized, i.e., elements can be added and removed.

Fixed-size array types have the form [T; N], where T is the element type, and N is the size of the array. N has to be statically known, meaning that it needs to be an integer literal. For example, a fixed-size array of 3 Int8 elements has the type [Int8; 3].

Variable-size array types have the form [T], where T is the element type. For example, the type [Int16] specifies a variable-size array of elements that have type Int16.

All values in an array must have a type which is a subtype of the array's element type (T).

It is important to understand that arrays are value types and are only ever copied when used as an initial value for a constant or variable, when assigning to a variable, when used as function argument, or when returned from a function call.

_26let size = 2_26// Invalid: Array-size must be an integer literal_26let numbers: [Int; size] = []_26_26// Declare a fixed-sized array of integers_26// which always contains exactly two elements._26//_26let array: [Int8; 2] = [1, 2]_26_26// Declare a fixed-sized array of fixed-sized arrays of integers._26// The inner arrays always contain exactly three elements,_26// the outer array always contains two elements._26//_26let arrays: [[Int16; 3]; 2] = [_26 [1, 2, 3],_26 [4, 5, 6]_26]_26_26// Declare a variable length array of integers_26var variableLengthArray: [Int] = []_26_26// Mixing values with different types is possible_26// by declaring the expected array type_26// with the common supertype of all values._26//_26let mixedValues: [AnyStruct] = ["some string", 42]

Array types are covariant in their element types. For example, [Int] is a subtype of [AnyStruct]. This is safe because arrays are value types and not reference types.

### Array Indexing​

To get the element of an array at a specific index, the indexing syntax can be used: The array is followed by an opening square bracket [, the indexing value, and ends with a closing square bracket ].

Indexes start at 0 for the first element in the array.

Accessing an element which is out of bounds results in a fatal error at run-time and aborts the program.

_14// Declare an array of integers._14let numbers = [42, 23]_14_14// Get the first number of the array._14//_14numbers[0] // is 42_14_14// Get the second number of the array._14//_14numbers[1] // is 23_14_14// Run-time error: Index 2 is out of bounds, the program aborts._14//_14numbers[2]
_10// Declare an array of arrays of integers, i.e. the type is [[Int]]._10let arrays = [[1, 2], [3, 4]]_10_10// Get the first number of the second array._10//_10arrays[1][0] // is 3

To set an element of an array at a specific index, the indexing syntax can be used as well.

_12// Declare an array of integers._12let numbers = [42, 23]_12_12// Change the second number in the array._12//_12// NOTE: The declaration numbers is constant, which means that_12// the *name* is constant, not the *value* – the value, i.e. the array,_12// is mutable and can be changed._12//_12numbers[1] = 2_12_12// numbers is [42, 2]

### Array Fields and Functions​

Arrays have multiple built-in fields and functions that can be used to get information about and manipulate the contents of the array.

The field length, and the functions concat, and contains are available for both variable-sized and fixed-sized or variable-sized arrays.

• _10let length: Int

The number of elements in the array.

_10// Declare an array of integers._10let numbers = [42, 23, 31, 12]_10_10// Find the number of elements of the array._10let length = numbers.length_10_10// length is 4
• _10access(all)_10fun concat(_ array: T): T

Concatenates the parameter array to the end of the array the function is called on, but does not modify that array.

Both arrays must be the same type T.

This function creates a new array whose length is the sum of the length of the array the function is called on and the length of the array given as the parameter.

_12// Declare two arrays of integers._12let numbers = [42, 23, 31, 12]_12let moreNumbers = [11, 27]_12_12// Concatenate the array moreNumbers to the array numbers_12// and declare a new variable for the result._12//_12let allNumbers = numbers.concat(moreNumbers)_12_12// allNumbers is [42, 23, 31, 12, 11, 27]_12// numbers is still [42, 23, 31, 12]_12// moreNumbers is still [11, 27]
• _10access(all)_10fun contains(_ element: T): Bool

Returns true if the given element of type T is in the array.

_15// Declare an array of integers._15let numbers = [42, 23, 31, 12]_15_15// Check if the array contains 11._15let containsEleven = numbers.contains(11)_15// containsEleven is false_15_15// Check if the array contains 12._15let containsTwelve = numbers.contains(12)_15// containsTwelve is true_15_15// Invalid: Check if the array contains the string "Kitty"._15// This results in a type error, as the array only contains integers._15//_15let containsKitty = numbers.contains("Kitty")
• _10access(all)_10fun firstIndex(of: T): Int?

Returns the index of the first element matching the given object in the array, nil if no match. Available if T is not resource-kinded and equatable.

_10 // Declare an array of integers._10 let numbers = [42, 23, 31, 12]_10_10 // Check if the array contains 31_10 let index = numbers.firstIndex(of: 31)_10 // index is 2_10_10 // Check if the array contains 22_10 let index = numbers.firstIndex(of: 22)_10 // index is nil
• _10access(all)_10fun slice(from: Int, upTo: Int): [T]

Returns an array slice of the elements in the given array from start index from up to, but not including, the end index upTo. This function creates a new array whose length is upTo - from. It does not modify the original array. If either of the parameters are out of the bounds of the array, or the indices are invalid (from > upTo), then the function will fail.

_11let example = [1, 2, 3, 4]_11_11// Create a new slice of part of the original array._11let slice = example.slice(from: 1, upTo: 3)_11// slice is now [2, 3]_11_11// Run-time error: Out of bounds index, the program aborts._11let outOfBounds = example.slice(from: 2, upTo: 10)_11_11// Run-time error: Invalid indices, the program aborts._11let invalidIndices = example.slice(from: 2, upTo: 1)
• _10access(all)_10fun reverse(): [T]

Returns a new array with contents in the reversed order. Available if T is not resource-kinded.

_10let example = [1, 2, 3, 4]_10_10// Create a new array which is the reverse of the original array._10let reversedExample = example.reverse()_10// reversedExample is now [4, 3, 2, 1]
_10access(all)_10fun reverse(): [T; N]

Returns a new fixed-sized array of same size with contents in the reversed order.

_10let fixedSizedExample: [String; 3] = ["ABC", "XYZ", "PQR"]_10_10// Create a new array which is the reverse of the original array._10let fixedArrayReversedExample = fixedSizedExample.reverse()_10// fixedArrayReversedExample is now ["PQR", "XYZ", "ABC"]
• _10access(all)_10fun map(_ f: (T: U)): [U]

Returns a new array whose elements are produced by applying the mapper function on each element of the original array. Available if T is not resource-kinded.

_18let example = [1, 2, 3]_18let trueForEven =_18 fun (_ x: Int): Bool {_18 return x % 2 == 0_18 }_18_18let mappedExample: [Bool] = example.map(trueForEven)_18// mappedExample is [False, True, False]_18// example still remains as [1, 2, 3]_18_18// Invalid: Map using a function which accepts a different type._18// This results in a type error, as the array contains Int values while function accepts _18// Int64._18let functionAcceptingInt64 =_18 fun (_ x: Int64): Bool {_18 return x % 2 == 0_18 }_18let invalidMapFunctionExample = example.map(functionAcceptingInt64)

map function is also available for fixed-sized arrays:

_10access(all)_10fun map(_ f: (T: U)): [U; N]

Returns a new fixed-sized array whose elements are produced by applying the mapper function on each element of the original array. Available if T is not resource-kinded.

_18let fixedSizedExample: [String; 3] = ["ABC", "XYZYX", "PQR"]_18let lengthOfString =_18 fun (_ x: String): Int {_18 return x.length_18 }_18_18let fixedArrayMappedExample = fixedSizedExample.map(lengthOfString)_18// fixedArrayMappedExample is now [3, 5, 3]_18// fixedSizedExample still remains as ["ABC", "XYZYX", "PQR"]_18_18// Invalid: Map using a function which accepts a different type._18// This results in a type error, as the array contains String values while function accepts _18// Bool._18let functionAcceptingBool =_18 fun (_ x: Bool): Int {_18 return 0_18 }_18let invalidMapFunctionExample = fixedSizedExample.map(functionAcceptingBool)

#### Variable-size Array Functions​

The following functions can only be used on variable-sized arrays. It is invalid to use one of these functions on a fixed-sized array.

• _10access(Mutate | Insert)_10fun append(_ element: T): Void

Adds the new element element of type T to the end of the array.

The new element must be the same type as all the other elements in the array.

This function mutates the array.

_10// Declare an array of integers._10let numbers = [42, 23, 31, 12]_10_10// Add a new element to the array._10numbers.append(20)_10// numbers is now [42, 23, 31, 12, 20]_10_10// Invalid: The parameter has the wrong type String._10numbers.append("SneakyString")
• _10access(Mutate | Insert)_10fun appendAll(_ array: T): Void

Adds all the elements from array to the end of the array the function is called on.

Both arrays must be the same type T.

This function mutates the array.

_10// Declare an array of integers._10let numbers = [42, 23]_10_10// Add new elements to the array._10numbers.appendAll([31, 12, 20])_10// numbers is now [42, 23, 31, 12, 20]_10_10// Invalid: The parameter has the wrong type [String]._10numbers.appendAll(["Sneaky", "String"])
• _10access(Mutate | Insert)_10fun insert(at: Int, _ element: T): Void

Inserts the new element element of type T at the given index of the array.

The new element must be of the same type as the other elements in the array.

The index must be within the bounds of the array. If the index is outside the bounds, the program aborts.

The existing element at the supplied index is not overwritten.

All the elements after the new inserted element are shifted to the right by one.

This function mutates the array.

_10// Declare an array of integers._10let numbers = [42, 23, 31, 12]_10_10// Insert a new element at position 1 of the array._10numbers.insert(at: 1, 20)_10// numbers is now [42, 20, 23, 31, 12]_10_10// Run-time error: Out of bounds index, the program aborts._10numbers.insert(at: 12, 39)
• _10access(Mutate | Remove)_10fun remove(at: Int): T

Removes the element at the given index from the array and returns it.

The index must be within the bounds of the array. If the index is outside the bounds, the program aborts.

This function mutates the array.

_10// Declare an array of integers._10let numbers = [42, 23, 31]_10_10// Remove element at position 1 of the array._10let twentyThree = numbers.remove(at: 1)_10// numbers is now [42, 31]_10// twentyThree is 23_10_10// Run-time error: Out of bounds index, the program aborts._10numbers.remove(at: 19)
• _10access(Mutate | Remove)_10fun removeFirst(): T

Removes the first element from the array and returns it.

The array must not be empty. If the array is empty, the program aborts.

This function mutates the array.

_15// Declare an array of integers._15let numbers = [42, 23]_15_15// Remove the first element of the array._15let fortytwo = numbers.removeFirst()_15// numbers is now [23]_15// fortywo is 42_15_15// Remove the first element of the array._15let twentyThree = numbers.removeFirst()_15// numbers is now []_15// twentyThree is 23_15_15// Run-time error: The array is empty, the program aborts._15numbers.removeFirst()
• _10access(Mutate | Remove)_10fun removeLast(): T

Removes the last element from the array and returns it.

The array must not be empty. If the array is empty, the program aborts.

This function mutates the array.

_15// Declare an array of integers._15let numbers = [42, 23]_15_15// Remove the last element of the array._15let twentyThree = numbers.removeLast()_15// numbers is now [42]_15// twentyThree is 23_15_15// Remove the last element of the array._15let fortyTwo = numbers.removeLast()_15// numbers is now []_15// fortyTwo is 42_15_15// Run-time error: The array is empty, the program aborts._15numbers.removeLast()

## Dictionaries​

Dictionaries are mutable, unordered collections of key-value associations. Dictionaries may contain a key only once and may contain a value multiple times.

Dictionary literals start with an opening brace { and end with a closing brace }. Keys are separated from values by a colon, and key-value associations are separated by commas.

_10// An empty dictionary_10//_10{}_10_10// A dictionary which associates integers with booleans_10//_10{_10 1: true,_10 2: false_10}

### Dictionary Types​

Dictionary types have the form {K: V}, where K is the type of the key, and V is the type of the value. For example, a dictionary with Int keys and Bool values has type {Int: Bool}.

In a dictionary, all keys must have a type that is a subtype of the dictionary's key type (K) and all values must have a type that is a subtype of the dictionary's value type (V).

_24// Declare a constant that has type {Int: Bool},_24// a dictionary mapping integers to booleans._24//_24let booleans = {_24 1: true,_24 0: false_24}_24_24// Declare a constant that has type {Bool: Int},_24// a dictionary mapping booleans to integers._24//_24let integers = {_24 true: 1,_24 false: 0_24}_24_24// Mixing keys with different types, and mixing values with different types,_24// is possible by declaring the expected dictionary type with the common supertype_24// of all keys, and the common supertype of all values._24//_24let mixedValues: {String: AnyStruct} = {_24 "a": 1,_24 "b": true_24}

Dictionary types are covariant in their key and value types. For example, {Int: String} is a subtype of {AnyStruct: String} and also a subtype of {Int: AnyStruct}. This is safe because dictionaries are value types and not reference types.

### Dictionary Access​

To get the value for a specific key from a dictionary, the access syntax can be used: The dictionary is followed by an opening square bracket [, the key, and ends with a closing square bracket ].

Accessing a key returns an optional: If the key is found in the dictionary, the value for the given key is returned, and if the key is not found, nil is returned.

_17// Declare a constant that has type {Int: Bool},_17// a dictionary mapping integers to booleans._17//_17let booleans = {_17 1: true,_17 0: false_17}_17_17// The result of accessing a key has type Bool?._17//_17booleans[1] // is true_17booleans[0] // is false_17booleans[2] // is nil_17_17// Invalid: Accessing a key which does not have type Int._17//_17booleans["1"]
_12// Declare a constant that has type {Bool: Int},_12// a dictionary mapping booleans to integers._12//_12let integers = {_12 true: 1,_12 false: 0_12}_12_12// The result of accessing a key has type Int?_12//_12integers[true] // is 1_12integers[false] // is 0

To set the value for a key of a dictionary, the access syntax can be used as well.

_13// Declare a constant that has type {Int: Bool},_13// a dictionary mapping booleans to integers._13//_13let booleans = {_13 1: true,_13 0: false_13}_13_13// Assign new values for the keys 1 and 0._13//_13booleans[1] = false_13booleans[0] = true_13// booleans is {1: false, 0: true}

### Dictionary Fields and Functions​

• _10let length: Int

The number of entries in the dictionary.

_10// Declare a dictionary mapping strings to integers._10let numbers = {"fortyTwo": 42, "twentyThree": 23}_10_10// Find the number of entries of the dictionary._10let length = numbers.length_10_10// length is 2
• _10access(Mutate | Insert)_10fun insert(key: K, _ value: V): V?

Inserts the given value of type V into the dictionary under the given key of type K.

The inserted key must have the same type as the dictionary's key type, and the inserted value must have the same type as the dictionary's value type.

Returns the previous value as an optional if the dictionary contained the key, otherwise nil.

This function mutates the dictionary.

_11// Declare a dictionary mapping strings to integers._11let numbers = {"twentyThree": 23}_11_11// Insert the key "fortyTwo" with the value 42 into the dictionary._11// The key did not previously exist in the dictionary,_11// so the result is nil_11//_11let old = numbers.insert(key: "fortyTwo", 42)_11_11// old is nil_11// numbers is {"twentyThree": 23, "fortyTwo": 42}
• _10fun remove(key: K): V?

Removes the value for the given key of type K from the dictionary.

Returns the value of type V as an optional if the dictionary contained the key, otherwise nil.

This function mutates the dictionary.

_19// Declare a dictionary mapping strings to integers._19let numbers = {"fortyTwo": 42, "twentyThree": 23}_19_19// Remove the key "fortyTwo" from the dictionary._19// The key exists in the dictionary,_19// so the value associated with the key is returned._19//_19let fortyTwo = numbers.remove(key: "fortyTwo")_19_19// fortyTwo is 42_19// numbers is {"twentyThree": 23}_19_19// Remove the key "oneHundred" from the dictionary._19// The key does not exist in the dictionary, so nil is returned._19//_19let oneHundred = numbers.remove(key: "oneHundred")_19_19// oneHundred is nil_19// numbers is {"twentyThree": 23}
• _10access(Mutate | Remove)_10let keys: [K]

Returns an array of the keys of type K in the dictionary. This does not modify the dictionary, just returns a copy of the keys as an array. If the dictionary is empty, this returns an empty array. The ordering of the keys is undefined.

_10// Declare a dictionary mapping strings to integers._10let numbers = {"fortyTwo": 42, "twentyThree": 23}_10_10// Find the keys of the dictionary._10let keys = numbers.keys_10_10// keys has type [String] and is ["fortyTwo","twentyThree"]
• _10let values: [V]

Returns an array of the values of type V in the dictionary. This does not modify the dictionary, just returns a copy of the values as an array. If the dictionary is empty, this returns an empty array.

This field is not available if V is a resource type.

_10// Declare a dictionary mapping strings to integers._10let numbers = {"fortyTwo": 42, "twentyThree": 23}_10_10// Find the values of the dictionary._10let values = numbers.values_10_10// values has type [Int] and is [42, 23]
• _10access(all)_10fun containsKey(key: K): Bool

Returns true if the given key of type K is in the dictionary.

_15// Declare a dictionary mapping strings to integers._15let numbers = {"fortyTwo": 42, "twentyThree": 23}_15_15// Check if the dictionary contains the key "twentyFive"._15let containsKeyTwentyFive = numbers.containsKey("twentyFive")_15// containsKeyTwentyFive is false_15_15// Check if the dictionary contains the key "fortyTwo"._15let containsKeyFortyTwo = numbers.containsKey("fortyTwo")_15// containsKeyFortyTwo is true_15_15// Invalid: Check if the dictionary contains the key 42._15// This results in a type error, as the key type of the dictionary is String._15//_15let containsKey42 = numbers.containsKey(42)
• _10access(all)_10fun forEachKey(_ function: fun(K): Bool): Void

Iterate through all the keys in the dictionary, exiting early if the passed function returns false. This is more efficient than calling .keys and iterating over the resulting array, since an intermediate allocation is avoided. The order of key iteration is undefined, similar to .keys.

_18// Take in a targetKey to look for, and a dictionary to iterate through._18fun myContainsKey(targetKey: String, dictionary: {String: Int}) {_18 // Declare an accumulator that we'll capture inside a closure._18 var found = false_18_18 // At each step, key will be bound to another key from dictionary._18 dictionary.forEachKey(fun (key: String): Bool {_18 found = key == targetKey_18_18 // The returned boolean value, signals whether to continue iterating._18 // This allows for control flow during the iteration process:_18 // true = continue_18 // false = break_18 return !found_18 })_18_18 return found_18}`

### Dictionary Keys​

Dictionary keys must be hashable and equatable.

Most of the built-in types, like booleans and integers, are hashable and equatable, so can be used as keys in dictionaries.