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  • Overriding rubies spaceship operator <=>

    - by ericsteen1
    I am trying to override rubies <= (spaceship) operator to sort apples and oranges so that apples come first sorted by weight, and oranges second, sorted by sweetness. Like so: module Fruity attr_accessor :weight, :sweetness def <=>(other) # use Array#<=> to compare the attributes [self.weight, self.sweetness] <=> [other.weight, other.sweetness] end include Comparable end class Apple include Fruity def initialize(w) self.weight = w end end class Orange include Fruity def initialize(s) self.sweetness = s end end fruits = [Apple.new(2),Orange.new(4),Apple.new(6),Orange.new(9),Apple.new(1),Orange.new(22)] p fruits #should work? p fruits.sort But this does not work, can someone tell what I am doing wrong here, or a better way to do this?

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  • Method Overloading for NULL parameter

    - by Phani
    I have added three methods with parameters: public static void doSomething(Object obj) { System.out.println("Object called"); } public static void doSomething(char[] obj) { System.out.println("Array called"); } public static void doSomething(Integer obj) { System.out.println("Array called"); } When I am calling doSomething(null) , then compiler throws error as ambiguous methods. So Is the issue because Integer and char[] methods or Integer and Object methods?

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  • Why is there no parameter contra-variance for overriding?

    - by Oak
    C++ and Java support return-type covariance when overriding methods. Neither, however, support contra-variance in parameter types - instead, it translates to overloading (Java) or hiding (C++). Why is that? It seems to me that there is no harm in allowing that. I can find one reason for it in Java - since it has the "choose-the-most-specific-version" mechanism for overloading anyway - but can't think of any reason for C++. Example (Java): class A { public void f(String s) {...} } class B extends A { public void f(Object o) {...} // Why doesn't this override A.f? }

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  • Limiting method access in protected section to few classes

    - by Bharat
    Hi, I want to limit the access of protected methods to certain inherited classes only. For example there is a base class like TBase = Class Protected Method1; Method2; Method3; Method4; End; I have two classes derived from TBase TDerived1 = Class(TBase) //Here i must access only Method1 and Method2 End; TDerived2 = Class(TBase) //Here i must access only Method3 and Method4 End; Then is it possible to access only Method1 and Method2 when i use objects of TDerived1 and Method3 and Method4 when i use objects of TDerived2

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  • In what circumstances are instance variables declared as '_var' in 'use fields' private?

    - by Pedro Silva
    I'm trying to understand the behavior of the fields pragma, which I find poorly documented, regarding fields prefixed with underscores. This is what the documentation has to say about it: Field names that start with an underscore character are made private to the class and are not visible to subclasses. Inherited fields can be overridden but will generate a warning if used together with the -w switch. This is not consistent with its actual behavior, according to my test, below. Not only are _-prefixed fields visible within a subclass, they are visible within foreign classes as well (unless I don't get what 'visible' means). Also, directly accessing the restricted hash works fine. Where can I find more about the behavior of the fields pragma, short of going at the source code? { package Foo; use strict; use warnings; use fields qw/a _b __c/; sub new { my ( $class ) = @_; my Foo $self = fields::new($class); $self->a = 1; $self->b = 2; $self->c = 3; return $self; } sub a : lvalue { shift->{a} } sub b : lvalue { shift->{_b} } sub c : lvalue { shift->{__c} } } { package Bar; use base 'Foo'; use strict; use warnings; use Data::Dumper; my $o = Bar->new; print Dumper $o; ##$VAR1 = bless({'_b' => 2, '__c' => 3, 'a' => 1}, 'Foo'); $o->a = 4; $o->b = 5; $o->c = 6; print Dumper $o; ##$VAR1 = bless({'_b' => 5, '__c' => 6, 'a' => 4}, 'Foo'); $o->{a} = 7; $o->{_b} = 8; $o->{__c} = 9; print Dumper $o; ##$VAR1 = bless({'_b' => 8, '__c' => 9, 'a' => 7}, 'Foo'); }

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  • Is this class + constructor definition pattern overly redundant?

    - by Protector one
    I often come across a pattern similar to this: class Person { public string firstName, lastName; public Person(string firstName, string lastName) { this.firstName = firstName; this.lastName = lastName; } } This feels overly redundant (I imagine typing "firstName" once, instead of thrice could be enough…), but I can't think of a proper alternative. Any ideas? Maybe I just don't know about a certain design pattern I should be using here? Edit - I think I need to elaborate a little. I'm not asking how to make the example code "better", but rather, "shorter". In its current state, all member names appear 3 times (declaration, initialization, constructor arguments), and it feels rather redundant. So I'm wondering if there is a pattern (or semantic sugar) to get (roughly) the same behavior, but with less bloat. I apologize for being unclear initially.

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  • Resetting Objects vs. Constructing New Objects

    - by byronh
    Is it considered better practice and/or more efficient to create a 'reset' function for a particular object that clears/defaults all the necessary member variables to allow for further operations, or to simply construct a new object from outside? I've seen both methods employed a lot, but I can't decide which one is better. Of course, for classes that represent database connections, you'd have to use a reset method rather than constructing a new one resulting in needless connecting/disconnecting, but I'm talking more in terms of abstraction classes. Can anyone give me some real-world examples of when to use each method? In my particular case I'm thinking mostly in terms of ORM or the Model in MVC. For example, if I would want to retrieve a bunch of database objects for display and modify them in one operation.

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  • An inaccessible class. VS2010.

    - by Mishgun_
    I realy dont know what the problem is with VS2010. I created a class, and when I'm trying create an exemplar of the class I get an error: "Error xxx is inaccessible due to its protection level. Example: public class Person { Person(string name, int age) { this.name = name; this.age = age; } public string name; public int age; } class Program { static void Main(string[] args) { Person ps = new Person("Jack", 19); } }

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  • accessing private variable from member function in PHP

    - by Carson Myers
    I have derived a class from Exception, basically like so: class MyException extends Exception { private $_type; public function type() { return $this->_type; //line 74 } public function __toString() { include "sometemplate.php"; return ""; } } Then, I derived from MyException like so: class SpecialException extends MyException { private $_type = "superspecial"; } If I throw new SpecialException("bla") from a function, catch it, and go echo $e, then the __toString function should load a template, display that, and then not actually return anything to echo. This is basically what's in the template file <div class="<?php echo $this->type(); ?>class"> <p> <?php echo $this->message; ?> </p> </div> in my mind, this should definitely work. However, I get the following error when an exception is thrown and I try to display it: Fatal error: Cannot access private property SpecialException::$_type in C:\path\to\exceptions.php on line 74 Can anyone explain why I am breaking the rules here? Am I doing something horribly witty with this code? Is there a much more idiomatic way to handle this situation? The point of the $_type variable is (as shown) that I want a different div class to be used depending on the type of exception caught.

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  • How can I add a field with an array value to my Perl object?

    - by superstar
    What's the difference between these two constructors in perl? 1) sub new { my $class = shift; my $self = {}; $self->{firstName} = undef; $self->{lastName} = undef; $self->{PEERS} = []; bless ($self, $class); return $self; } 2) sub new { my $class = shift; my $self = { _firstName => shift, _lastName => shift, _ssn => shift, }; bless $self, $class; return $self; } I am using the second one so far, but I need to implement the PEERS array in the second one? How do I do it with the second constructor and how can we use get and set methods on those array variables?

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  • Python and classes

    - by Artyom
    Hello, i have 2 classes. How i call first.TQ in Second ? Without creating object First in Second. class First: def __init__(self): self.str = "" def TQ(self): pass def main(self): T = Second(self.str) # Called here class Second(): def __init__(self): list = {u"RANDINT":first.TQ} # List of funcs maybe called in first ..... ..... return data

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  • PHP Classes: Call method in instance of a class by instance's name

    - by Ursus Russus
    Hi, i have a class of this kind Class Car { private $color; public function __construct($color){ $this->color=$color; } public function get_color(){ return $this->$color; } } Then i create some instances of it: $blue_car = new car('blue'); $green_car = new car('green'); etc. Now i need to call method get_color() on the fly, according to instance's name $instance_name='green_car'; Is there any way to do it?

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  • How do I change the URL Alias for Security/login in SilverStripe to user/login

    - by pthurmond
    I am working on a new website being built in SilverStripe. Currently I am having a ton of trouble trying to get the system to let me change the URL alias (or create a second one) for the Security controller's login (and eventually logout) function. I have tried playing around with the routes.yml file and I tried creating the paths in my own UserController and loading directly from the Security controller with "return Security::login()". But that gives me errors about the use of the static functions. Unfortunately I don't come from a ton of object oriented experience and this is the first CMS I have used that actually uses a bunch of true object orientation. The current version of SilverStripe we are using is 3.0 (but we will be upgrading to 3.1.1 in a few days). Does anyone know much about the routing in SilverStripe?

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  • C# Design a class with interface?

    - by Haroon
    I am having a bit of trouble understanding how I will design a class. My class will have 3 methods ICollection<Field> GetFields(); //perform validation internally - return back the object T UpdateFields(ICollection<Field> fields); //pass in model object with values on it, set up fields, then pass back all fields ICollection<Field> GetFieldsWithValues(T object); What is the best way to construct/design such a class keeping in mind: 1. The model object I pass in will be one of 3 or 4 tables, however when I call GetFIelds - internally for each object I know what fields will be there i.e. list.add(new Field{name = "id", value = "5"}); list.add(new Field{name = "nameofcompany", value = "super guys"});

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  • How to work with PHP abstract?

    - by YumYumYum
    Why would you use such abstract? Does it speed up work or what exactly its for? // file1.php abstract class Search_Adapter_Abstract { private $ch = null; abstract private function __construct() { } abstract public funciton __destruct() { curl_close($this->ch); } abstract public function search($searchString,$offset,$count); } // file2.php include("file1.php"); class abc extends Search_Adapter_Abstract { // Will the curl_close now automatically be closed? } What is the reason of extending abstract here? Makes me confused. What can i get from it now?

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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  • How to prevent inheritance for some methods?!

    - by Dr TJ
    Hi How can I prevent inheritance of some methods or properties in derived classes?! public class BaseClass : Collection { //Some operations... //Should not let derived classes inherit 'Add' method. } public class DerivedClass : BaseClass { public void DoSomething(int Item) { this.Add(Item); // Error: No such method should exist... } }

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  • Java - how to tell class of an object?

    - by lkm
    Given a method that accepts as a parameter a certain supertype. Is there any way, within that method, to determine the actual class of the object that was passed to it? I.e. if a subtype of the allowable parameter was actually passed, is there a way to find out which type it is? If this isn't possible can someone explain why not (from a language design perspective)? Thanks Update: just to make sure I was clear void doSomething(MyType myType) { //determine if myType is MyType OR one of its subclasses } Since the method signature specifies the parameter as being MyType, then how can one tell if the object is actually a subtype of MyType (and which one).

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  • real time scenario between interface/abstract class ?

    - by JavaUser
    Hi , Please give me a real time simple example for the below questions : Where to use interface rather abstract class Where to use abstract class rather interface I need code snippet for both . Which takes low memory and which performs well . Do I need to consider the design aspect also? What is the conceptual difference not the syntactical difference .

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  • Method return values and exceptions

    - by dnagirl
    I have an interface called iIncident which defines a single method when(). when() should return a DateTime object. I'm trying to decide what to do if $object->when() has no DateTime to return as might be the case just after an object is instantiated and before all its properties are set. My choices are: return false throw some kind of Exception return some default DateTime like '9999-01-01' My inclination is to go with an Exception since $object really can't act as an incident until it knows when it occurred. I don't want to return a default DateTime because it complicates comparisons and it's not true. And I don't really want to return false because then I have to check for it every time I call the method- but if that is the preferred method, I guess I will. Is throwing an exception the best way? And is there a predefined exception type I should use (none of the SPL ones struck me as particularly appropriate- but that might just indicate my lack of experience)?

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  • Example of forum in Object Oriented PHP

    - by Martin Trigaux
    Hello, I'm trying to learn to use PHP with an object oriented scheme. I think I understand the concept but I need real example, a forum exactly (the closest to what I want to do). I know PhpBB but it's maybe too complicated to fully understand it so I'm looking for something simpler but still in object oriented. Do you know any ? Thank you

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