operator-overloading

问题 Sorry for the poor title, I don't really know what to call this. I have something like this in Ruby: class Test def initialize @my_array = [] end attr_accessor :my_array end test = Test.new test.my_array << "Hello, World!" For the @my_array instance variable, I want to override the << operator so that I can first process whatever is being inserted to it. I've tried @my_array.<<(value) as a method in the class, but it didn't work. 回答1: I think you're looking for this: class Test def initialize

问题 I'm trying to write an abstract class with some pure virtual binary operators, which should be implemented by the derived class in order to accomplish operator polymorphism. Here's a simplified example: class Base { public: virtual const Base& operator+ (const Base&) const = 0; }; class Derived : public Base { public: const Derived& operator+ (const Derived&) const; }; const Derived& Derived::operator+ (const Derived& rvalue) const { return Derived(); } It doesn't matter right now what the

问题 The reinterpret_cast as we know can cast any pointer type to any another pointer type. The question I want to ask regarding this cast operator are: How does reinterpret_cast work, What is the magic(the internal implementation) that allows reinterpret_cast to work? How to ensure safety when using reinterpret_cast ? As far as i know, it doesn't guarantee of safe casting, So what precaution to take while using reinterpret_cast? What is the practical usage of this operator. I have not really

问题 The reinterpret_cast as we know can cast any pointer type to any another pointer type. The question I want to ask regarding this cast operator are: How does reinterpret_cast work, What is the magic(the internal implementation) that allows reinterpret_cast to work? How to ensure safety when using reinterpret_cast ? As far as i know, it doesn't guarantee of safe casting, So what precaution to take while using reinterpret_cast? What is the practical usage of this operator. I have not really

问题 How can I overload the |= operator on a strongly typed (scoped) enum (in C++11, GCC)? I want to test, set and clear bits on strongly typed enums. Why strongly typed? Because my books say it is good practice. But this means I have to static_cast<int> everywhere. To prevent this, I overload the | and & operators, but I can't figure out how to overload the |= operator on an enum . For a class you'd simply put the operator definition in the class, but for enums that doesn't seem to work

问题 I want to create extension functions for classes that encapsulate simple Number s. For example DoubleProperty . I encountered the problem, that I can't overload the + and the += operator at the same time. I wan't to create a behaviour, that passes following tests: class DoublePropertyTest { lateinit var doubleProperty: DoubleProperty @Before fun initialize() { doubleProperty = SimpleDoubleProperty(0.1) } @Test fun plus() { val someProperty = doubleProperty + 1.5 assertEquals(someProperty

问题 I have a Rectangle class with conversion operators to both double and std::string : class Rectangle { public: Rectangle(double x, double y) : _x(x), _y(y) {} operator std::string (); operator double (); private: double _x, _y; double getArea() {return _x * _y;} }; int main() { Rectangle r(3, 2.5); cout << r << endl; return 0; } I don’t understand why operator double() is invoked, rather than operator std::string() . As far as I know, according to C++ wikibook, operator double is used to

问题 When you are going to print an object, a friend operator<< is used. Can we use member function for operator<< ? class A { public: void operator<<(ostream& i) { i<<"Member function";} friend ostream& operator<<(ostream& i, A& a) { i<<"operator<<"; return i;} }; int main () { A a; A b; A c; cout<<a<<b<<c<<endl; a<<cout; return 0; } One point is that friend function enable us to use it like this cout<<a<<b<<c What other reasons? 回答1: You have to use a free function and not a member function as

问题 I have a Grid class which I want to access using myGrid[1][2] . I know I can overload the first set of square brackets with the __getitem__() method, but what about the second. I thought I could achieve this by having a helper class which also implements __getitem__ and then: class Grid: def __init__(self) self.list = A TWO DIMENSIONAL LIST ... def __getitem__(self, index): return GridIndexHelper(self, index) class GridIndexHelper: def __init__(self, grid, index1): self.grid = grid self

问题 i've been messing around with ruby and opengl for entertainment purposes, and i decided to write some 3d vector/plane/etc classes to pretty up some of the math. simplified example: class Vec3 attr_accessor :x,:y,:z def *(a) if a.is_a?(Numeric) #multiply by scalar return Vec3.new(@x*a, @y*a, @z*a) elsif a.is_a?(Vec3) #dot product return @x*a.x + @y*a.y + @z*a.z end end end v1 = Vec3.new(1,1,1) v2 = v1*5 #produces [5,5,5] which all fine and dandy, but i also want to be able to write v2 = 5*v1