abstraction

>> a = 5 => 5 >> b = "hello, world!" => "hello, world!" >> b.dup => "hello, world!" >> a.dup TypeError: can't dup Fixnum from (irb):4:in `dup' from (irb):4 I understand that Ruby will make a copy every time you assign an integer to a new variable, but why does Numeric#dup raise an error? Wouldn't this break abstraction, since all objects should be expected to respond to .dup properly? Rewriting the dup method will fix the problem, as far as I can tell: >> class Numeric >> def dup() >> self >> end >> end Does this have a downside I'm not seeing? Why isn't this built into Ruby? Most objects in

The following code will have PHP unhappy that customMethod() is private. Why is this the case? Is visibility determined by where something is declared rather than defined? If I wanted to make customMethod only visible to boilerplate code in the Template class and prevent it from being overriden, would I just alternatively make it protected and final? Template.php: abstract class Template() { abstract private function customMethod(); public function commonMethod() { $this->customMethod(); } } CustomA.php: class CustomA extends Template { private function customMethod() { blah... } } Main.php ..

... absolutely nothing? What part of the puzzle does it fill for ASP.NET WebForms and ASP.NET MVC respectively? Can you somehow create a ASP.NET * base-application which uses System.Web.Abstractions so it can be used in both kinds of ASP.NET-web applications? In that case, how did they retro-fit the classes in System.Web.Abstractions back into ASP.NET WebForms? You can't new up objects from the namespace, so it can't be used for mocking, can it? Update : Sorry for not being clear on that I know the problem with testing of HttpContext and other build-it ASP.NET-objects. But thanks for good

I was reading a thread from CodeRanch saying that abstract methods could not be synchronized due to the fact that an abstract class cannot be instantiated, meaning no object to lock. This doesn't make sense since an abstract class is a definition (contract) for a child class. The abstract definition of a synchronized method does not need to lock, the child does. All the abstract heading would indicate is that the child must synchronize this method. Is my logic on this correct? If not can someone explain why I'm wrong? The comment about not being able to instantiate the abstract class is

Consider the Object-Oriented Languages: Most people coming from an object-oriented programming background, are familiar with the common and intuitive interfaces in various languages that capture the essence of Java's Collection & List interfaces. Collection refers to a collection of objects which doesn't necessarily have an natural ordering/indexing. A List is a collection which has a natural ordering/indexing. These interfaces abstract many library data-structures in Java, as do their equivalent interfaces in other languages, and an intimate understanding of these interfaces are required to

I seem to not understand two OOP concepts very well. Could you explain what abstraction and polymorphism are, preferably with real examples and code? Thank you. Abstraction Imagine a fraction class: class fraction: int denominator int numerator Now two objects of that: fraction(obj1): denominator=-1 numerator=-1 fraction(obj2): denominator=1 numerator=1 Both objects have the value 1: (1/1) == (-1)/(-1) . You wouldn't expect they behave any different to the outside. That's abstraction. You abstract the data your object holds into a logical view, even tho behind the scenes, there are other

The answers to questions like this: List<T> or IList<T> always seem to agree that returning an interface is better than returning a concrete implementation of a collection. But I'm struggling with this. Instantiating an interface is impossible, so if your method is returning an interface, it's actually still returning a specific implementation. I was experimenting a bit with this by writing 2 small methods: public static IList<int> ExposeArrayIList() { return new[] { 1, 2, 3 }; } public static IList<int> ExposeListIList() { return new List<int> { 1, 2, 3 }; } And use them in my test program: