No, there is not. To overload operator==, you must provide a user-defined type as one of the operands and a pointer (either AString* or const char*) does not qualify. And when comparing two pointers, the compiler has a very adequate built-in operator==, so it will not consider converting one of the arguments to a class … Read more
The reason is a combination of several facts. You want to be able to chain input and output operations as in in >> x >> y; out << z << std::precision(10) << t << std::endl; so you must return something that allows operator<< again. Since you want your operator to work on any istream, i.e. … Read more
What you propose would create two different usage patterns for nullable types. Consider the following code: bool? a = null; // This doesn’t currently compile but would with lifted true/false operators. if (a) { } // Whereas this provides a consistent use of nullable types. if (a ?? false) { } For consistency in the … Read more
I agree that the equal function on the vector prototype is the best solution. Note that you can also build other infix-like operators via chaining. function Vector(x, y, z) { this.x = x; this.y = y; this.z = z; } Vector.prototype.add = function (v2) { var v = new Vector(this.x + v2.x, this.y + v2.y, … Read more
This can be used to create “functors”, objects that act like functions: class Multiplier { public: Multiplier(int m): multiplier(m) {} int operator()(int x) { return multiplier * x; } private: int multiplier; }; Multiplier m(5); cout << m(4) << endl; The above prints 20. The Wikipedia article linked above gives more substantial examples.
You’re missing a key exception to the usual behaviour: when the right-hand operand is an instance of a subclass of the class of the left-hand operand, the special method for the right-hand operand is called first. See the documentation at: http://docs.python.org/reference/datamodel.html#coercion-rules and in particular, the following two paragraphs: For objects x and y, first x.__op__(y) … Read more
SQLAlchemy is a great example. For the uninitiated, SQLAlchemy is a ORM and uses Python expression to generate SQL statements. In a expression such as meta.Session.query(model.Theme).filter(model.Theme.id == model.Vote.post_id) the model.Theme.id == model.VoteWarn.post_id does not return a boolean, but a object that eventually produces a SQL query like WHERE theme.id = vote.post_id. The inverse would produce … Read more
There’s a big difference between overloading == and overriding Equals. When you have the expression if (x == y) { The method that will be used to compare variables x and y is decided at compile time. This is operator overloading. The type used when declaring x and y is used to define which method … Read more
The operator-> has special semantics in the language in that, when overloaded, it reapplies itself to the result. While the rest of the operators are applied only once, operator-> will be applied by the compiler as many times as needed to get to a raw pointer and once more to access the memory referred by … Read more
The problem is that you define it inside the class, which a) means the second argument is implicit (this) and b) it will not do what you want it do, namely extend std::ostream. You have to define it as a free function: class A { /* … */ }; std::ostream& operator<<(std::ostream&, const A& a);