Swift运算符函数与自定义运算符

代码：

struct Vector2D {
    var x = 0.0, y = 0.0
}

// vector1 + vector2
func + (left: Vector2D, right: Vector2D) -> Vector2D {
    return Vector2D(x: left.x + right.x, y: left.y + right.y)
}

// vector1 - vector2
func - (left: Vector2D, right: Vector2D) -> Vector2D {
    return Vector2D(x: left.x - right.x, y: left.y - right.y)
}

// -vector
prefix func - (vector: Vector2D) -> Vector2D {
    return Vector2D(x: -vector.x, y: -vector.y)
}

// vector1 += vector2
func += (inout left: Vector2D, right: Vector2D) {
    left = left + right
}

// vector1 -= vector2
func -= (inout left: Vector2D, right: Vector2D) {
    left = left - right
}

// ++vector1
prefix func ++ (inout v: Vector2D) -> Vector2D {
    v += Vector2D(x: 1, y: 1)
    return v
}
// vector1++
postfix func ++ (inout v: Vector2D) -> Vector2D {
    v += Vector2D(x: 1, y: 1)
    return v
}

// --vector
prefix func -- (inout v: Vector2D) -> Vector2D {
    v += Vector2D(x: 1, y: 1)
    return v
}

// vector--
postfix func -- (inout v: Vector2D) -> Vector2D {
    v += Vector2D(x: 1, y: 1)
    return v
}

// vector1 == vector2
func == (left: Vector2D, right: Vector2D) -> Bool {
    return (left.x == right.x) && (left.y == right.y)
}

// vector1 != vector2
func != (left: Vector2D, right: Vector2D) -> Bool {
    return !(left == right)
}

// +++vector
prefix operator +++ {}
prefix func +++ (inout vector: Vector2D) -> Vector2D {
    vector += vector
    return vector
}

// vector+++
postfix operator +++ {}
postfix func +++ (inout vector: Vector2D) -> Vector2D {
    vector += vector
    return vector
}

// vector1 +- vector2
infix operator +- { associativity left precedence 140 }
func +- (left: Vector2D, right: Vector2D) -> Vector2D {
    return Vector2D(x: left.x + right.x, y: left.y - right.y)
}

// vector1 -+ vector2
infix operator -+ { associativity left precedence 140 }
func -+ (left: Vector2D, right: Vector2D) -> Vector2D {
    return Vector2D(x: left.x - right.x, y: left.y + right.y)
}