# Operators

Operators are special symbols that perform a computation for one or more values. They are either unary, binary, or ternary.

• Unary operators perform an operation for a single value. The unary operator symbol appears before the value.

• Binary operators operate on two values. The binary operator symbol appears between the two values (infix).

• Ternary operators operate on three values. The first operator symbol appears between the first and second value, the second operator symbol appears between the second and third value (infix).

## Assignment Operator (=)​

The binary assignment operator = can be used to assign a new value to a variable. It is only allowed in a statement and is not allowed in expressions.

_14var a = 1_14a = 2_14// a is 2_14_14_14var b = 3_14var c = 4_14_14// Invalid: The assignment operation cannot be used in an expression._14a = b = c_14_14// Instead, the intended assignment must be written in multiple statements._14b = c_14a = b

Assignments to constants are invalid.

_10let a = 1_10// Invalid: Assignments are only for variables, not constants._10a = 2

The left-hand side of the assignment operand must be an identifier. For arrays and dictionaries, this identifier can be followed by one or more index or access expressions.

_10// Declare an array of integers._10let numbers = [1, 2]_10_10// Change the first element of the array._10//_10numbers = 3_10_10// numbers is [3, 2]
_10// Declare an array of arrays of integers._10let arrays = [[1, 2], [3, 4]]_10_10// Change the first element in the second array_10//_10arrays = 5_10_10// arrays is [[1, 2], [5, 4]]
_11let dictionaries = {_11 true: {1: 2},_11 false: {3: 4}_11}_11_11dictionaries[false] = 0_11_11// dictionaries is {_11// true: {1: 2},_11// false: {3: 0}_11//}

## Force-assignment operator (<-!)​

The force-assignment operator (<-!) assigns a resource-typed value to an optional-typed variable if the variable is nil. If the variable being assigned to is non-nil, the execution of the program aborts.

The force-assignment operator is only used for resource types.

## Swapping Operator (<->)​

The binary swap operator <-> can be used to exchange the values of two variables. It is only allowed in a statement and is not allowed in expressions.

_14var a = 1_14var b = 2_14a <-> b_14// a is 2_14// b is 1_14_14var c = 3_14_14// Invalid: The swap operation cannot be used in an expression._14a <-> b <-> c_14_14// Instead, the intended swap must be written in multiple statements._14b <-> c_14a <-> b

Both sides of the swap operation must be variable, assignment to constants is invalid.

_10var a = 1_10let b = 2_10_10// Invalid: Swapping is only possible for variables, not constants._10a <-> b

Both sides of the swap operation must be an identifier, followed by one or more index or access expressions.

## Arithmetic Operators​

The unary pefix operator - negates an integer:

_10let a = 1_10-a // is -1

There are four binary arithmetic operators:

• Addition: +
• Subtraction: -
• Multiplication: *
• Division: /
• Remainder: %
_10let a = 1 + 2_10// a is 3

The arguments for the operators need to be of the same type. The result is always the same type as the arguments.

The division and remainder operators abort the program when the divisor is zero.

Arithmetic operations on the signed integer types Int8, Int16, Int32, Int64, Int128, Int256, and on the unsigned integer types UInt8, UInt16, UInt32, UInt64, UInt128, UInt256, do not cause values to overflow or underflow.

_10let a: UInt8 = 255_10_10// Run-time error: The result 256 does not fit in the range of UInt8,_10// thus a fatal overflow error is raised and the program aborts_10//_10let b = a + 1
_10let a: Int8 = 100_10let b: Int8 = 100_10_10// Run-time error: The result 10000 does not fit in the range of Int8,_10// thus a fatal overflow error is raised and the program aborts_10//_10let c = a * b
_10let a: Int8 = -128_10_10// Run-time error: The result 128 does not fit in the range of Int8,_10// thus a fatal overflow error is raised and the program aborts_10//_10let b = -a

Arithmetic operations on the unsigned integer types Word8, Word16, Word32, Word64 may cause values to overflow or underflow.

For example, the maximum value of an unsigned 8-bit integer is 255 (binary 11111111). Adding 1 results in an overflow, truncation to 8 bits, and the value 0.

_10// 11111111 = 255_10// + 1_10// = 100000000 = 0
_10let a: Word8 = 255_10a + 1 // is 0

Similarly, for the minimum value 0, subtracting 1 wraps around and results in the maximum value 255.

_10// 00000000_10// - 1_10// = 11111111 = 255
_10let b: Word8 = 0_10b - 1 // is 255

### Arithmetics on number super-types​

Arithmetic operators are not supported for number supertypes (Number, SignedNumber, FixedPoint, SignedFixedPoint, Integer, SignedInteger), as they may or may not succeed at run-time.

_10let x: Integer = 3 as Int8_10let y: Integer = 4 as Int8_10_10let z: Integer = x + y // Static error

Values of these types need to be cast to the desired type before performing the arithmetic operation.

_10let z: Integer = (x as! Int8) + (y as! Int8)

## Logical Operators​

Logical operators work with the boolean values true and false.

• Logical NOT: !a

This unary prefix operator logically negates a boolean:

_10let a = true_10!a // is false
• Logical AND: a && b

_10true && true // is true_10_10true && false // is false_10_10false && true // is false_10_10false && false // is false

If the left-hand side is false, the right-hand side is not evaluated.

• Logical OR: a || b

_10true || true // is true_10_10true || false // is true_10_10false || true // is true_10_10false || false // is false

If the left-hand side is true, the right-hand side is not evaluated.

## Comparison Operators​

Comparison operators work with boolean and integer values.

• Equality: ==, is supported for booleans, numbers, addresses, strings, characters, enums, paths, Type values, references, and Void values (()). Variable-sized arrays, fixed-size arrays, dictionaries, and optionals also support equality tests if their inner types do.

Both sides of the equality operator may be optional, even of different levels, so it is for example possible to compare a non-optional with a double-optional (??).

_101 == 1 // is true_10_101 == 2 // is false
_10true == true // is true_10_10true == false // is false
_10let x: Int? = 1_10x == nil // is false
_10let x: Int = 1_10x == nil // is false
_10// Comparisons of different levels of optionals are possible._10let x: Int? = 2_10let y: Int?? = nil_10x == y // is false
_10// Comparisons of different levels of optionals are possible._10let x: Int? = 2_10let y: Int?? = 2_10x == y // is true
_10// Equality tests of arrays are possible if their inner types are equatable._10let xs: [Int] = [1, 2, 3]_10let ys: [Int] = [1, 2, 3]_10xs == ys // is true_10_10let xss: [[Int]] = [xs, xs, xs]_10let yss: [[Int]] = [ys, ys, ys]_10xss == yss // is true
_10// Equality also applies to fixed-size arrays. If their lengths differ, the result is a type error._10let xs: [Int; 2] = [1, 2]_10let ys: [Int; 2] = [0 + 1, 1 + 1]_10xs == ys // is true
_10// Equality tests of dictionaries are possible if the key and value types are equatable._10let d1 = {"abc": 1, "def": 2}_10let d2 = {"abc": 1, "def": 2}_10d1 == d2 // is true_10_10let d3 = {"abc": {1: {"a": 1000}, 2: {"b": 2000}}, "def": {4: {"c": 1000}, 5: {"d": 2000}}}_10let d4 = {"abc": {1: {"a": 1000}, 2: {"b": 2000}}, "def": {4: {"c": 1000}, 5: {"d": 2000}}}_10d3 == d4 // is true
• Inequality: !=, is supported for booleans, numbers, addresses, strings, characters, enums, paths, Type values, references, and Void values (()). Variable-sized arrays, fixed-size arrays, dictionaries, and optionals also support inequality tests if their inner types do.

Both sides of the inequality operator may be optional, even of different levels, so it is for example possible to compare a non-optional with a double-optional (??).

_101 != 1 // is false_10_101 != 2 // is true
_10true != true // is false_10_10true != false // is true
_10let x: Int? = 1_10x != nil // is true
_10let x: Int = 1_10x != nil // is true
_10// Comparisons of different levels of optionals are possible._10let x: Int? = 2_10let y: Int?? = nil_10x != y // is true
_10// Comparisons of different levels of optionals are possible._10let x: Int? = 2_10let y: Int?? = 2_10x != y // is false
_10// Inequality tests of arrays are possible if their inner types are equatable._10let xs: [Int] = [1, 2, 3]_10let ys: [Int] = [4, 5, 6]_10xs != ys // is true
_10// Inequality also applies to fixed-size arrays. If their lengths differ, the result is a type error._10let xs: [Int; 2] = [1, 2]_10let ys: [Int; 2] = [1, 2]_10xs != ys // is false
_10// Inequality tests of dictionaries are possible if the key and value types are equatable._10let d1 = {"abc": 1, "def": 2}_10let d2 = {"abc": 1, "def": 500}_10d1 != d2 // is true_10_10let d3 = {"abc": {1: {"a": 1000}, 2: {"b": 2000}}, "def": {4: {"c": 1000}, 5: {"d": 2000}}}_10let d4 = {"abc": {1: {"a": 1000}, 2: {"b": 2000}}, "def": {4: {"c": 1000}, 5: {"d": 2000}}}_10d3 != d4 // is false
• Less than: <, for integers, booleans, characters and strings

_231 < 1 // is false_23_231 < 2 // is true_23_232 < 1 // is false_23_23false < true // is true_23_23true < true // is false_23_23"a" < "b" // is true_23_23"z" < "a" // is false_23_23"a" < "A" // is false_23_23"" < "" // is false_23_23"" < "a" // is true_23_23"az" < "b" // is true_23_23"xAB" < "Xab" // is false
• Less or equal than: <=, for integers, booleans, characters and strings

_251 <= 1 // is true_25_251 <= 2 // is true_25_252 <= 1 // is false_25_25false <= true // is true_25_25true <= true // is true_25_25true <= false // is false_25_25"c" <= "a" // is false_25_25"z" <= "z" // is true_25_25"a" <= "A" // is false_25_25"" <= "" // is true_25_25"" <= "a" // is true_25_25"az" <= "b" // is true_25_25"xAB" <= "Xab" // is false
• Greater than: >, for integers, booleans, characters and strings

_251 > 1 // is false_25_251 > 2 // is false_25_252 > 1 // is true_25_25false > true // is false_25_25true > true // is false_25_25true > false // is true_25_25"c" > "a" // is true_25_25"g" > "g" // is false_25_25"a" > "A" // is true_25_25"" > "" // is false_25_25"" > "a" // is false_25_25"az" > "b" // is false_25_25"xAB" > "Xab" // is true
• Greater or equal than: >=, for integers, booleans, characters and strings

_251 >= 1 // is true_25_251 >= 2 // is false_25_252 >= 1 // is true_25_25false >= true // is false_25_25true >= true // is true_25_25true >= false // is true_25_25"c" >= "a" // is true_25_25"q" >= "q" // is true_25_25"a" >= "A" // is true_25_25"" >= "" // is true_25_25"" >= "a" // is true_25_25"az" >= "b" // is true_25_25"xAB" >= "Xab" // is false

### Comparing number super-types​

Similar to arithmetic operators, comparison operators are also not supported for number supertypes (Number, SignedNumber FixedPoint, SignedFixedPoint, Integer, SignedInteger), as they may or may not succeed at run-time.

_10let x: Integer = 3 as Int8_10let y: Integer = 4 as Int8_10_10let z: Bool = x > y // Static error

Values of these types need to be cast to the desired type before performing the arithmetic operation.

_10let z: Bool = (x as! Int8) > (y as! Int8)

## Bitwise Operators​

Bitwise operators enable the manipulation of individual bits of unsigned and signed integers. They're often used in low-level programming.

• Bitwise AND: a & b

Returns a new integer whose bits are 1 only if the bits were 1 in both input integers:

_10let firstFiveBits = 0b11111000_10let lastFiveBits = 0b00011111_10let middleTwoBits = firstFiveBits & lastFiveBits // is 0b00011000
• Bitwise OR: a | b

Returns a new integer whose bits are 1 only if the bits were 1 in either input integers:

_10let someBits = 0b10110010_10let moreBits = 0b01011110_10let combinedbits = someBits | moreBits // is 0b11111110
• Bitwise XOR: a ^ b

Returns a new integer whose bits are 1 where the input bits are different, and are 0 where the input bits are the same:

_10let firstBits = 0b00010100_10let otherBits = 0b00000101_10let outputBits = firstBits ^ otherBits // is 0b00010001

### Bitwise Shifting Operators​

• Bitwise LEFT SHIFT: a << b

Returns a new integer with all bits moved to the left by a certain number of places.

_10let someBits = 4 // is 0b00000100_10let shiftedBits = someBits << 2 // is 0b00010000
• Bitwise RIGHT SHIFT: a >> b

Returns a new integer with all bits moved to the right by a certain number of places.

_10let someBits = 8 // is 0b00001000_10let shiftedBits = someBits >> 2 // is 0b00000010

For unsigned integers, the bitwise shifting operators perform logical shifting, for signed integers, they perform arithmetic shifting.

## Ternary Conditional Operator​

There is only one ternary conditional operator, the ternary conditional operator (a ? b : c).

It behaves like an if-statement, but is an expression: If the first operator value is true, the second operator value is returned. If the first operator value is false, the third value is returned.

The first value must be a boolean (must have the type Bool). The second value and third value can be of any type. The result type is the least common supertype of the second and third value.

_10let x = 1 > 2 ? 3 : 4_10// x is 4 and has type Int_10_10let y = 1 > 2 ? nil : 3_10// y is 3 and has type Int?

## Casting Operators​

### Static Casting Operator (as)​

The static casting operator as can be used to statically type cast a value to a type.

If the static type of the value is a subtype of the given type (the "target" type), the operator returns the value as the given type.

The cast is performed statically, i.e. when the program is type-checked. Only the static type of the value is considered, not the run-time type of the value.

This means it is not possible to downcast using this operator. Consider using the conditional downcasting operator as? instead.

_22// Declare a constant named integer which has type Int._22//_22let integer: Int = 1_22_22// Statically cast the value of integer to the supertype Number._22// The cast succeeds, because the type of the variable integer,_22// the type Int, is a subtype of type Number._22// This is an upcast._22//_22let number = integer as Number_22// number is 1 and has type Number_22_22// Declare a constant named something which has type AnyStruct,_22// with an initial value which has type Int._22//_22let something: AnyStruct = 1_22_22// Statically cast the value of something to Int._22// This is invalid, the cast fails, because the static type of the value is type AnyStruct,_22// which is not a subtype of type Int._22//_22let result = something as Int

### Conditional Downcasting Operator (as?)​

The conditional downcasting operator as? can be used to dynamically type cast a value to a type. The operator returns an optional. If the value has a run-time type that is a subtype of the target type the operator returns the value as the target type, otherwise the result is nil.

The cast is performed at run-time, i.e. when the program is executed, not statically, i.e. when the program is checked.

_17// Declare a constant named something which has type AnyStruct,_17// with an initial value which has type Int._17//_17let something: AnyStruct = 1_17_17// Conditionally downcast the value of something to Int._17// The cast succeeds, because the value has type Int._17//_17let number = something as? Int_17// number is 1 and has type Int?_17_17// Conditionally downcast the value of something to Bool._17// The cast fails, because the value has type Int,_17// and Bool is not a subtype of Int._17//_17let boolean = something as? Bool_17// boolean is nil and has type Bool?

Downcasting works for concrete types, but also works e.g. for nested types (e.g. arrays), interfaces, optionals, etc.

_10// Declare a constant named values which has type [AnyStruct],_10// i.e. an array of arbitrarily typed values._10//_10let values: [AnyStruct] = [1, true]_10_10let first = values as? Int_10// first is 1 and has type Int?_10_10let second = values as? Bool_10// second is true and has type Bool?

### Force-downcasting Operator (as!)​

The force-downcasting operator as! behaves like the conditional downcasting operator as?. However, if the cast succeeds, it returns a value of the given type instead of an optional, and if the cast fails, it aborts the program instead of returning nil,

_17// Declare a constant named something which has type AnyStruct,_17// with an initial value which has type Int._17//_17let something: AnyStruct = 1_17_17// Force-downcast the value of something to Int._17// The cast succeeds, because the value has type Int._17//_17let number = something as! Int_17// number is 1 and has type Int_17_17// Force-downcast the value of something to Bool._17// The cast fails, because the value has type Int,_17// and Bool is not a subtype of Int._17//_17let boolean = something as! Bool_17// Run-time error

## Optional Operators​

### Nil-Coalescing Operator (??)​

The nil-coalescing operator ?? returns the value inside an optional if it contains a value, or returns an alternative value if the optional has no value, i.e., the optional value is nil.

If the left-hand side is non-nil, the right-hand side is not evaluated.

_10// Declare a constant which has an optional integer type_10//_10let a: Int? = nil_10_10// Declare a constant with a non-optional integer type,_10// which is initialized to a if it is non-nil, or 42 otherwise._10//_10let b: Int = a ?? 42_10// b is 42, as a is nil

The nil-coalescing operator can only be applied to values which have an optional type.

_10// Declare a constant with a non-optional integer type._10//_10let a = 1_10_10// Invalid: nil-coalescing operator is applied to a value which has a non-optional type_10// (a has the non-optional type Int)._10//_10let b = a ?? 2
_10// Invalid: nil-coalescing operator is applied to a value which has a non-optional type_10// (the integer literal is of type Int)._10//_10let c = 1 ?? 2

The type of the right-hand side of the operator (the alternative value) must be a subtype of the type of left-hand side, i.e. the right-hand side of the operator must be the non-optional or optional type matching the type of the left-hand side.

_11// Declare a constant with an optional integer type._11//_11let a: Int? = nil_11let b: Int? = 1_11let c = a ?? b_11// c is 1 and has type Int?_11_11// Invalid: nil-coalescing operator is applied to a value of type Int?,_11// but the alternative has type Bool._11//_11let d = a ?? false

### Force Unwrap Operator (!)​

The force-unwrap operator (!) 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.

_19// Declare a constant which has an optional integer type_19//_19let a: Int? = nil_19_19// Declare a constant with a non-optional integer type,_19// which is initialized to a if a is non-nil._19// If a is nil, the program aborts._19//_19let b: Int = a!_19// The program aborts because a is nil._19_19// Declare another optional integer constant_19let c: Int? = 3_19_19// Declare a non-optional integer_19// which is initialized to c if c is non-nil._19// If c is nil, the program aborts._19let d: Int = c!_19// d is initialized to 3 because c isn't nil.

The force-unwrap operator can only be applied to values which have an optional type.

_10// Declare a constant with a non-optional integer type._10//_10let a = 1_10_10// Invalid: force-unwrap operator is applied to a value which has a_10// non-optional type (a has the non-optional type Int)._10//_10let b = a!
_10// Invalid: The force-unwrap operator is applied_10// to a value which has a non-optional type_10// (the integer literal is of type Int)._10//_10let c = 1!

## Precedence and Associativity​

Operators have the following precedences, highest to lowest:

• Unary precedence: -, !, <-
• Cast precedence: as, as?, as!
• Multiplication precedence: *, /, %
• Addition precedence: +, -
• Bitwise shift precedence: <<, >>
• Bitwise conjunction precedence: &
• Bitwise exclusive disjunction precedence: ^
• Bitwise disjunction precedence: |
• Nil-Coalescing precedence: ??
• Relational precedence: <, <=, >, >=
• Equality precedence: ==, !=
• Logical conjunction precedence: &&
• Logical disjunction precedence: ||
• Ternary precedence: ? :

All operators are left-associative, except for the following operators which are right-associative:

• Ternary operator
• Nil-coalescing operator

Expressions can be wrapped in parentheses to override precedence conventions, i.e. an alternate order should be indicated, or when the default order should be emphasized e.g. to avoid confusion. For example, (2 + 3) * 4 forces addition to precede multiplication, and 5 + (6 * 7) reinforces the default order.