language-features

I've missed the memo somewhere, and I hope you'll explain this to me. Why is the eigenclass of an object different from self.class ? class Foo def initialize(symbol) eigenclass = class << self self end eigenclass.class_eval do attr_accessor symbol end end end My train of logic that equates the eigenclass with class.self is rather simple: class << self is a way of declaring class methods, rather than instance methods. It's a shortcut to def Foo.bar . So within the reference to the class object, returning self should be identical to self.class . This is because class << self would set self to

Inspired by this discussion , after some googling I wasn't able to find an answer to a pretty simple question regarding methods in Ruby: are methods objects or not? There are different opinions here and there , and I would really like to hear, let's say, an in-depth explanation. I'm aware of Object#method method, which takes a method name and returns a Method instance, but, on the other hand, there's a similar thing you can do with blocks to make them into Proc instances, and blocks aren't objects, so what makes methods any different? JRL Methods are a fundamental part of Ruby's syntax, but

In JavaScript, there are two values which basically say 'I don't exist' - undefined and null . A property to which a programmer has not assigned anything will be undefined , but in order for a property to become null , null must be explicitly assigned to it. I once thought that there was a need for null because undefined is a primitive value and null an object. It's not, even if typeof null will yield 'object' : Actually, both are primitive values - which means neither undefined nor null can be returned from a constructor function, as both will be converted to an empty object (one has to throw

I have heard/read the term but don't quite understand what it means. When should I use this technique and how would I use it? Can anyone provide a good code sample? The visitor pattern is a way of doing double-dispatch in an object-oriented way. It's useful for when you want to choose which method to use for a given argument based on its type at runtime rather than compile time. Double dispatch is a special case of multiple dispatch . When you call a virtual method on an object, that's considered single-dispatch because which actual method is called depends on the type of the single object.

I would like to properly understand hashes in Perl. I've had to use Perl intermittently for quite some time and mostly whenever I need to do it, it's mostly related to text processing. And everytime, I have to deal with hashes, it gets messed up. I find the syntax very cryptic for hashes A good explanation of hashes and hash references, their differences, when they are required etc. would be much appreciated. A simple hash is close to an array. Their initializations even look similar. First the array: @last_name = ( "Ward", "Cleaver", "Fred", "Flintstone", "Archie", "Bunker" ); Now let's

In C# (and many other languages) it's perfectly legitimate to access private fields of other instances of the same type. For example: public class Foo { private bool aBool; public void DoBar(Foo anotherFoo) { if (anotherFoo.aBool) ... } } As the C# specification (sections 3.5.1, 3.5.2) states access to private fields is on a type, not an instance. I've been discussing this with a colleague and we're trying to come up with a reason why it works like this (rather than restricting access to the same instance). The best argument we could come up with is for equality checks where the class may want