To summarize the contents of other (already good!) answers, isinstance caters for inheritance (an instance of a derived class is an instance of a base class, too), while checking for equality of type does not (it demands identity of types and rejects instances of subtypes, AKA subclasses). Normally, in Python, you want your code to … Read more
class A { public: int x; protected: int y; private: int z; }; class B : public A { // x is public // y is protected // z is not accessible from B }; class C : protected A { // x is protected // y is protected // z is not accessible from … Read more
There are some good answers here. I would add to them the following points. What is the correct C# way of representing a data structure, which, “logically” (that is to say, “to the human mind”) is just a list of things with a few bells and whistles? Ask any ten non-computer-programmer people who are familiar … Read more
On invoking overridable method from constructors Simply put, this is wrong because it unnecessarily opens up possibilities to MANY bugs. When the @Override is invoked, the state of the object may be inconsistent and/or incomplete. A quote from Effective Java 2nd Edition, Item 17: Design and document for inheritance, or else prohibit it: There are … Read more
Short answer: in order to make x a dependent name, so that lookup is deferred until the template parameter is known. Long answer: when a compiler sees a template, it is supposed to perform certain checks immediately, without seeing the template parameter. Others are deferred until the parameter is known. It’s called two-phase compilation, and … Read more
@Bill Karwin describes three inheritance models in his SQL Antipatterns book, when proposing solutions to the SQL Entity-Attribute-Value antipattern. This is a brief overview: Single Table Inheritance (aka Table Per Hierarchy Inheritance): Using a single table as in your first option is probably the simplest design. As you mentioned, many attributes that are subtype-specific will … Read more
Quick answer: A child scope normally prototypically inherits from its parent scope, but not always. One exception to this rule is a directive with scope: { … } — this creates an “isolate” scope that does not prototypically inherit. This construct is often used when creating a “reusable component” directive. As for the nuances, scope … Read more
Constructor function introduction You can use a function as a constructor to create objects, if the constructor function is named Person then the object(s) created with that constructor are instances of Person. var Person = function(name){ this.name = name; }; Person.prototype.walk=function(){ this.step().step().step(); }; var bob = new Person(“Bob”); Person is the constructor function. When you … Read more
No, a List<Dog> is not a List<Animal>. Consider what you can do with a List<Animal> – you can add any animal to it… including a cat. Now, can you logically add a cat to a litter of puppies? Absolutely not. // Illegal code – because otherwise life would be Bad List<Dog> dogs = new ArrayList<Dog>(); … Read more
“Slicing” is where you assign an object of a derived class to an instance of a base class, thereby losing part of the information – some of it is “sliced” away. For example, class A { int foo; }; class B : public A { int bar; }; So an object of type B has … Read more