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 (=
)â€‹
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 lefthand 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[0] = 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[1][0] = 5_10_10// `arrays` is `[[1, 2], [5, 4]]`
_11let dictionaries = {_11 true: {1: 2},_11 false: {3: 4}_11}_11_11dictionaries[false][3] = 0_11_11// `dictionaries` is `{_11// true: {1: 2},_11// false: {3: 0}_11//}`
Forceassignment operator (<!
)â€‹
The forceassignment operator (<!
) assigns a resourcetyped value
to an optionaltyped variable if the variable is nil.
If the variable being assigned to is nonnil,
the execution of the program aborts.
The forceassignment operator is only used for resource types.
Swapping Operator (<>
)â€‹
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 Operatorsâ€‹
The unary pefix operator 
negates an integer:
_10let a = 1_10a // 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// Runtime 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// Runtime 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// Runtime 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 8bit 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 supertypesâ€‹
Arithmetic operators are not supported for number supertypes
(Number
, SignedNumber
, FixedPoint
, SignedFixedPoint
, Integer
, SignedInteger
),
as they may or may not succeed at runtime.
_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 Operatorsâ€‹
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 lefthand side is false, the righthand 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 lefthand side is true, the righthand side is not evaluated.
Comparison Operatorsâ€‹
Comparison operators work with boolean and integer values.

Equality:
==
, is supported for booleans, numbers, addresses, strings, characters, enums, paths,Type
values, references, andVoid
values (()
). Variablesized arrays, fixedsize 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 nonoptional with a doubleoptional (
??
)._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 fixedsize 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, andVoid
values (()
). Variablesized arrays, fixedsize 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 nonoptional with a doubleoptional (
??
)._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 fixedsize 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 supertypesâ€‹
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 runtime.
_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 Operatorsâ€‹
Bitwise operators enable the manipulation of individual bits of unsigned and signed integers. They're often used in lowlevel 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 Operatorsâ€‹

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.
Also note that for a << b
or a >> b
, b
must fit into a 64bit integer.
Ternary Conditional Operatorâ€‹
There is only one ternary conditional operator, the ternary conditional operator (a ? b : c
).
It behaves like an ifstatement, 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 Operatorsâ€‹
Static Casting Operator (as
)â€‹
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 typechecked. Only the static type of the value is considered, not the runtime 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?
)â€‹
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 runtime 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 runtime, 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[0] as? Int_10// `first` is `1` and has type `Int?`_10_10let second = values[1] as? Bool_10// `second` is `true` and has type `Bool?`
Forcedowncasting Operator (as!
)â€‹
The forcedowncasting 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// Forcedowncast 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// Forcedowncast 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// Runtime error
Optional Operatorsâ€‹
NilCoalescing Operator (??
)â€‹
The nilcoalescing 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 lefthand side is nonnil, the righthand 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 nonoptional integer type,_10// which is initialized to `a` if it is nonnil, or 42 otherwise._10//_10let b: Int = a ?? 42_10// `b` is 42, as `a` is nil
The nilcoalescing operator can only be applied to values which have an optional type.
_10// Declare a constant with a nonoptional integer type._10//_10let a = 1_10_10// Invalid: nilcoalescing operator is applied to a value which has a nonoptional type_10// (a has the nonoptional type `Int`)._10//_10let b = a ?? 2
_10// Invalid: nilcoalescing operator is applied to a value which has a nonoptional type_10// (the integer literal is of type `Int`)._10//_10let c = 1 ?? 2
The type of the righthand side of the operator (the alternative value) must be a subtype of the type of lefthand side, i.e. the righthand side of the operator must be the nonoptional or optional type matching the type of the lefthand 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: nilcoalescing operator is applied to a value of type `Int?`,_11// but the alternative has type `Bool`._11//_11let d = a ?? false
Force Unwrap Operator (!
)â€‹
The forceunwrap 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 nonoptional integer type,_19// which is initialized to `a` if `a` is nonnil._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 nonoptional integer_19// which is initialized to `c` if `c` is nonnil._19// If `c` is nil, the program aborts._19let d: Int = c!_19// `d` is initialized to 3 because c isn't nil.
The forceunwrap operator can only be applied to values which have an optional type.
_10// Declare a constant with a nonoptional integer type._10//_10let a = 1_10_10// Invalid: forceunwrap operator is applied to a value which has a_10// nonoptional type (`a` has the nonoptional type `Int`)._10//_10let b = a!
_10// Invalid: The forceunwrap operator is applied_10// to a value which has a nonoptional type_10// (the integer literal is of type `Int`)._10//_10let c = 1!
Precedence and Associativityâ€‹
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:

 NilCoalescing precedence:
??
 Relational precedence:
<
,<=
,>
,>=
 Equality precedence:
==
,!=
 Logical conjunction precedence:
&&
 Logical disjunction precedence:

 Ternary precedence:
? :
All operators are leftassociative, except for the following operators which are rightassociative:
 Ternary operator
 Nilcoalescing 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.