operator prefix - { associativity precedence } Declarations prefix func -(_: Double) Calculates the additive inverse of a value. The unary minus operator (prefix -) calculates the negation of its operand. The result is always exact. let x = 21.5 let y = -x // y == -21.5 operand: The value to negate. Declaration prefix func -(x: Double) -> Double prefix func -(_: Float) Calculates the additive inverse of a value. The unary minus operator (prefix -) calculates the negation of its operand. The result is always exact. let x = 21.5 let y = -x // y == -21.5 operand: The value to negate. Declaration prefix func -(x: Float) -> Float prefix func -(_: Float80) Calculates the additive inverse of a value. The unary minus operator (prefix -) calculates the negation of its operand. The result is always exact. let x = 21.5 let y = -x // y == -21.5 operand: The value to negate. Declaration prefix func -(x: Float80) -> Float80 Declared In Float80, BinaryFloatingPoint, SignedNumeric