## Advanced Operators ~~~ let initialBits: UInt8 = 0b00001111 let invertedBits = ~initialBits // equals 11110000 let firstSixBits: UInt8 = 0b11111100 let lastSixBits: UInt8 = 0b00111111 let middleFourBits = firstSixBits & lastSixBits // equals 00111100 let someBits: UInt8 = 0b10110010 let moreBits: UInt8 = 0b01011110 let combinedbits = someBits | moreBits // equals 11111110 let firstBits: UInt8 = 0b00010100 let otherBits: UInt8 = 0b00000101 let outputBits = firstBits ^ otherBits // equals 00010001 let shiftBits: UInt8 = 4 // 00000100 in binary shiftBits << 1 // 00001000 shiftBits << 2 // 00010000 shiftBits << 5 // 10000000 shiftBits << 6 // 00000000 shiftBits >> 2 // 00000001 let pink: UInt32 = 0xCC6699 let redComponent = (pink & 0xFF0000) >> 16 // redComponent is 0xCC, or 204 let greenComponent = (pink & 0x00FF00) >> 8 // greenComponent is 0x66, or 102 let blueComponent = pink & 0x0000FF // blueComponent is 0x99, or 153 // 如果允许溢出，在运算符前加& var willOverflow = UInt8.max // willOverflow equals 255, which is the largest value a UInt8 can hold willOverflow = willOverflow &+ 1 // willOverflow is now equal to 0 var willUnderflow = UInt8.min // willUnderflow equals 0, which is the smallest value a UInt8 can hold willUnderflow = willUnderflow &- 1 // willUnderflow is now equal to 255 var signedUnderflow = Int8.min // signedUnderflow equals -128, which is the smallest value an Int8 can hold signedUnderflow = signedUnderflow &- 1 // signedUnderflow is now equal to 127 ~~~ 运算符重载： ~~~ struct Vector2D { var x = 0.0, y = 0.0 } // It is said to be infix because it appears in between those two targets. @infix func + (left: Vector2D, right: Vector2D) -> Vector2D { return Vector2D(x: left.x + right.x, y: left.y + right.y) } let vector = Vector2D(x: 3.0, y: 1.0) let anotherVector = Vector2D(x: 2.0, y: 4.0) let combinedVector = vector + anotherVector // combinedVector is a Vector2D instance with values of (5.0, 5.0) @prefix func - (vector: Vector2D) -> Vector2D { return Vector2D(x: -vector.x, y: -vector.y) } let positive = Vector2D(x: 3.0, y: 4.0) let negative = -positive // negative is a Vector2D instance with values of (-3.0, -4.0) let alsoPositive = -negative // alsoPositive is a Vector2D instance with values of (3.0, 4.0) // 复合赋值运算符 @assignment func += (inout left: Vector2D, right: Vector2D) { left = left + right } var original = Vector2D(x: 1.0, y: 2.0) let vectorToAdd = Vector2D(x: 3.0, y: 4.0) original += vectorToAdd // original now has values of (4.0, 6.0) @prefix @assignment func ++ (inout vector: Vector2D) -> Vector2D { vector += Vector2D(x: 1.0, y: 1.0) return vector } var toIncrement = Vector2D(x: 3.0, y: 4.0) let afterIncrement = ++toIncrement // toIncrement now has values of (4.0, 5.0) // afterIncrement also has values of (4.0, 5.0) ~~~ It is not possible to overload the default assignment operator (=). Only the compound assignment operators can be overloaded. Similarly, the ternary conditional operator (a ? b : c) cannot be overloaded. ~~~ // Equivalence Operators @infix func == (left: Vector2D, right: Vector2D) -> Bool { return (left.x == right.x) && (left.y == right.y) } @infix func != (left: Vector2D, right: Vector2D) -> Bool { return !(left == right) } let twoThree = Vector2D(x: 2.0, y: 3.0) let anotherTwoThree = Vector2D(x: 2.0, y: 3.0) if twoThree == anotherTwoThree { println("These two vectors are equivalent.") } // prints "These two vectors are equivalent." ~~~ Custom operators can be defined only with the characters / = - + * % ! & | ^ . ~. New operators are declared at a global level using the operator keyword, and can be declared as prefix, infix or postfix: ~~~ operator prefix +++ {} @prefix @assignment func +++ (inout vector: Vector2D) -> Vector2D { vector += vector return vector } var toBeDoubled = Vector2D(x: 1.0, y: 4.0) let afterDoubling = +++toBeDoubled // toBeDoubled now has values of (2.0, 8.0) // afterDoubling also has values of (2.0, 8.0) ~~~ Precedence and Associativity for Custom Infix Operators ~~~ operator infix +- { associativity left precedence 140 } func +- (left: Vector2D, right: Vector2D) -> Vector2D { return Vector2D(x: left.x + right.x, y: left.y - right.y) } let firstVector = Vector2D(x: 1.0, y: 2.0) let secondVector = Vector2D(x: 3.0, y: 4.0) let plusMinusVector = firstVector +- secondVector // plusMinusVector is a Vector2D instance with values of (4.0, -2.0) ~~~