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  • Hints to properly design UML class diagram

    - by mic4ael
    Here is the problem. I have just started learning UML and that is why I would like to ask for a few cues from experienced users how I could improve my diagram because I do know it lacks a lot of details, it has mistakes for sure etc. Renovation company hires workers. Each employee has some kind of profession, which is required to work on a particular position. Workers work in groups consisting of at most 15 members - so called production units, which specializes in a specified kind of work. Each production unit is managed by a foreman. Every worker in order to be able to perform job tasks needs proper accessories. There are two kind of tools - light and heavy. To use heavy tools, a worker must have proper privileges. A worker can have at most 3 light tools taken from the warehouse.

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  • Isn't class scope purely for organization?

    - by Di-0xide
    Isn't scope just a way to organize classes, preventing outside code from accessing certain things you don't want accessed? More specifically, is there any functional gain to having public, protected, or private-scoped methods? Is there any advantage to classifying method/property scope rather than to, say, just public-ize everything? My presumption says no simply because, in binary code, there is no sense of scope (other than r/w/e, which isn't really scope at all, but rather global permissions for a block of memory). Is this correct? What about in languages like Java and C#[.NET]?

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  • What class structure allows for a base class and mix/match of subclasses? (Similar to Users w/ roles)

    - by cdeszaq
    I have a set of base characteristics, and then a number of sub-types. Each instance must be one of the sub-types, but can be multiple sub-types at once. The sub-types of each thing can change. In general, I don't care what subtype I have, but sometimes I do care. This is much like a Users-Roles sort of relationship where a User having a particular Role gives the user additional characteristics. Sort of like duck-typing (ie. If my Foo has a Bar, I can treat it like a ThingWithABar.) Straight inheritance doesn't work, since that doesn't allow mix/match of sub-types. (ie. no multi-inheritance). Straight composition doesn't work because I can't switch that up at runtime. How can I model this?

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  • Different buddy lists for different accounts in iChat

    - by Idlecool
    I have currently 4 accounts added to iChat, Standard GTalk GTalk For Google Apps Facebook Olark Facebook and Olark have their own Buddy List Group viz. Facebook and WebUser groups and thus those buddies come in a separate list, while the buddies from GTalk and GTalk from Google Apps do not have any group associated with them and they come under Buddies list. It's a bit of a pain because I want to have buddies from GTalk for Google Apps in a separate buddy list than the default one. Is it possible to do it in iChat?

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  • how can i select first second or third element with given class name using CSS?

    - by Tumharyyaaden
    ie. i have the following: <div class="myclass">my text1</div> some other code+containers... <div class="myclass">my text2</div> some other code+containers... <div class="myclass">my text3</div> some other code+containers... i have the css class div.myclass {doing things} that applies to all obviously but i also wanted to be able to select the first, second or third like this: div.myclass:first {color:#000;} div.myclass:second {color:#FFF;} div.myclass:third {color:#006;} almost like the jQuery index selection .eq( index ) which is what i am using currently but need a noscript alternative. Thanks in advance!

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  • Accessing every child class of parent class in Java

    - by darkie15
    Hi All, I have to implement a logic whereby given a child class, I need to access its parent class and all other child class of that parent class, if any. I did not find any API in Java Reflection which allows us to access all child classes of a parent class. Is there any way to do it? Ex. class B extends class A class C extends class A Now using class B, I can find the superclass by calling getSuperClass(). But is there any way to find all the child classes once I have the parent class i.e. class B and class C?? Regards, darkie

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  • Some confusion with a class variable, but with a twist...

    - by Omega
    I have a class called MyPackage.WebServer and it has a property called DBEngine. I am also dynamically loading a module and class using load_module. Inside this class, it attempts to reference MyPackage.WebServer. When it does though, DBEngine is not set to the value given when WebServer is instantiated. It's the default (None). Would the fact that I'm using load_module cause a different object graph to be created and thus isolate my dynamically loaded class from the rest of my python app?

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  • "Public" nested classes or not

    - by Frederick
    Suppose I have a class 'Application'. In order to be initialised it takes certain settings in the constructor. Let's also assume that the number of settings is so many that it's compelling to place them in a class of their own. Compare the following two implementations of this scenario. Implementation 1: class Application { Application(ApplicationSettings settings) { //Do initialisation here } } class ApplicationSettings { //Settings related methods and properties here } Implementation 2: class Application { Application(Application.Settings settings) { //Do initialisation here } class Settings { //Settings related methods and properties here } } To me, the second approach is very much preferable. It is more readable because it strongly emphasises the relation between the two classes. When I write code to instantiate Application class anywhere, the second approach is going to look prettier. Now just imagine the Settings class itself in turn had some similarly "related" class and that class in turn did so too. Go only three such levels and the class naming gets out out of hand in the 'non-nested' case. If you nest, however, things still stay elegant. Despite the above, I've read people saying on StackOverflow that nested classes are justified only if they're not visible to the outside world; that is if they are used only for the internal implementation of the containing class. The commonly cited objection is bloating the size of containing class's source file, but partial classes is the perfect solution for that problem. My question is, why are we wary of the "publicly exposed" use of nested classes? Are there any other arguments against such use?

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  • Is It "Wrong"/Bad Design To Put A Thread/Background Worker In A Class?

    - by Jetti
    I have a class that will read from Excel (C# and .Net 4) and in that class I have a background worker that will load the data from Excel while the UI can remain responsive. My question is as follows: Is it bad design to have a background worker in a class? Should I create my class without it and use a background worker to operate on that class? I can't see any issues really of creating my class this way but then again I am a newbie so I figured I would make sure before I continue on. I hope that this question is relevant here as I don't think it should be on stackoverflow as my code works, this just a design issue.

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  • VB.NET class inherits a base class and implements an interface issue (works in C#)

    - by 300 baud
    I am trying to create a class in VB.NET which inherits a base abstract class and also implements an interface. The interface declares a string property called Description. The base class contains a string property called Description. The main class inherits the base class and implements the interface. The existence of the Description property in the base class fulfills the interface requirements. This works fine in C# but causes issues in VB.NET. First, here is an example of the C# code which works: public interface IFoo { string Description { get; set; } } public abstract class FooBase { public string Description { get; set; } } public class MyFoo : FooBase, IFoo { } Now here is the VB.NET version which gives a compiler error: Public Interface IFoo Property Description() As String End Interface Public MustInherit Class FooBase Private _Description As String Public Property Description() As String Get Return _Description End Get Set(ByVal value As String) _Description = value End Set End Property End Class Public Class MyFoo Inherits FooBase Implements IFoo End Class If I make the base class (FooBase) implement the interface and add the Implements IFoo.Description to the property all is good, but I do not want the base class to implement the interface. The compiler error is: Class 'MyFoo' must implement 'Property Description() As String' for interface 'IFoo'. Implementing property must have matching 'ReadOnly' or 'WriteOnly' specifiers. Can VB.NET not handle this, or do I need to change my syntax somewhere to get this to work?

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  • Accessing parent class attribute from sub-class body

    - by warwaruk
    I have a class Klass with a class attribute my_list. I have a subclass of it SubKlass, in which i want to have a class attribute my_list which is a modified version of the same attribute from parent class: class Klass(): my_list = [1, 2, 3] class SubKlass(Klass): my_list = Klass.my_list + [4, 5] # this works, but i must specify parent class explicitly #my_list = super().my_list + [4, 5] # SystemError: super(): __class__ cell not found #my_list = my_list + [4, 5] # NameError: name 'my_list' is not defined print(Klass.my_list) print(SubKlass.my_list) So, is there a way to access parent class attribute without specifying its name?

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  • Objective-C Class Question?

    - by tarnfeld
    Hey, My head is about to explode with this logic, can anyone help? Class A #imports Class B. Class A calls Method A in Class B. This works great Class B wants to send a response back to Class A from another method that is called from Method A. If you #import Class A from Class B, it is in effect an infinite loop and the whole thing crashes. Is there a way to do this properly, like a parent type thing? BTW, I'm developing for iPhone.

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  • Followup: Python 2.6, 3 abstract base class misunderstanding

    - by Aaron
    I asked a question at Python 2.6, 3 abstract base class misunderstanding. My problem was that python abstract base classes didn't work quite the way I expected them to. There was some discussion in the comments about why I would want to use ABCs at all, and Alex Martelli provided an excellent answer on why my use didn't work and how to accomplish what I wanted. Here I'd like to address why one might want to use ABCs, and show my test code implementation based on Alex's answer. tl;dr: Code after the 16th paragraph. In the discussion on the original post, statements were made along the lines that you don't need ABCs in Python, and that ABCs don't do anything and are therefore not real classes; they're merely interface definitions. An abstract base class is just a tool in your tool box. It's a design tool that's been around for many years, and a programming tool that is explicitly available in many programming languages. It can be implemented manually in languages that don't provide it. An ABC is always a real class, even when it doesn't do anything but define an interface, because specifying the interface is what an ABC does. If that was all an ABC could do, that would be enough reason to have it in your toolbox, but in Python and some other languages they can do more. The basic reason to use an ABC is when you have a number of classes that all do the same thing (have the same interface) but do it differently, and you want to guarantee that that complete interface is implemented in all objects. A user of your classes can rely on the interface being completely implemented in all classes. You can maintain this guarantee manually. Over time you may succeed. Or you might forget something. Before Python had ABCs you could guarantee it semi-manually, by throwing NotImplementedError in all the base class's interface methods; you must implement these methods in derived classes. This is only a partial solution, because you can still instantiate such a base class. A more complete solution is to use ABCs as provided in Python 2.6 and above. Template methods and other wrinkles and patterns are ideas whose implementation can be made easier with full-citizen ABCs. Another idea in the comments was that Python doesn't need ABCs (understood as a class that only defines an interface) because it has multiple inheritance. The implied reference there seems to be Java and its single inheritance. In Java you "get around" single inheritance by inheriting from one or more interfaces. Java uses the word "interface" in two ways. A "Java interface" is a class with method signatures but no implementations. The methods are the interface's "interface" in the more general, non-Java sense of the word. Yes, Python has multiple inheritance, so you don't need Java-like "interfaces" (ABCs) merely to provide sets of interface methods to a class. But that's not the only reason in software development to use ABCs. Most generally, you use an ABC to specify an interface (set of methods) that will likely be implemented differently in different derived classes, yet that all derived classes must have. Additionally, there may be no sensible default implementation for the base class to provide. Finally, even an ABC with almost no interface is still useful. We use something like it when we have multiple except clauses for a try. Many exceptions have exactly the same interface, with only two differences: the exception's string value, and the actual class of the exception. In many exception clauses we use nothing about the exception except its class to decide what to do; catching one type of exception we do one thing, and another except clause catching a different exception does another thing. According to the exception module's doc page, BaseException is not intended to be derived by any user defined exceptions. If ABCs had been a first class Python concept from the beginning, it's easy to imagine BaseException being specified as an ABC. But enough of that. Here's some 2.6 code that demonstrates how to use ABCs, and how to specify a list-like ABC. Examples are run in ipython, which I like much better than the python shell for day to day work; I only wish it was available for python3. Your basic 2.6 ABC: from abc import ABCMeta, abstractmethod class Super(): __metaclass__ = ABCMeta @abstractmethod def method1(self): pass Test it (in ipython, python shell would be similar): In [2]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods method1 Notice the end of the last line, where the TypeError exception tells us that method1 has not been implemented ("abstract methods method1"). That was the method designated as @abstractmethod in the preceding code. Create a subclass that inherits Super, implement method1 in the subclass and you're done. My problem, which caused me to ask the original question, was how to specify an ABC that itself defines a list interface. My naive solution was to make an ABC as above, and in the inheritance parentheses say (list). My assumption was that the class would still be abstract (can't instantiate it), and would be a list. That was wrong; inheriting from list made the class concrete, despite the abstract bits in the class definition. Alex suggested inheriting from collections.MutableSequence, which is abstract (and so doesn't make the class concrete) and list-like. I used collections.Sequence, which is also abstract but has a shorter interface and so was quicker to implement. First, Super derived from Sequence, with nothing extra: from abc import abstractmethod from collections import Sequence class Super(Sequence): pass Test it: In [6]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods __getitem__, __len__ We can't instantiate it. A list-like full-citizen ABC; yea! Again, notice in the last line that TypeError tells us why we can't instantiate it: __getitem__ and __len__ are abstract methods. They come from collections.Sequence. But, I want a bunch of subclasses that all act like immutable lists (which collections.Sequence essentially is), and that have their own implementations of my added interface methods. In particular, I don't want to implement my own list code, Python already did that for me. So first, let's implement the missing Sequence methods, in terms of Python's list type, so that all subclasses act as lists (Sequences). First let's see the signatures of the missing abstract methods: In [12]: help(Sequence.__getitem__) Help on method __getitem__ in module _abcoll: __getitem__(self, index) unbound _abcoll.Sequence method (END) In [14]: help(Sequence.__len__) Help on method __len__ in module _abcoll: __len__(self) unbound _abcoll.Sequence method (END) __getitem__ takes an index, and __len__ takes nothing. And the implementation (so far) is: from abc import abstractmethod from collections import Sequence class Super(Sequence): # Gives us a list member for ABC methods to use. def __init__(self): self._list = [] # Abstract method in Sequence, implemented in terms of list. def __getitem__(self, index): return self._list.__getitem__(index) # Abstract method in Sequence, implemented in terms of list. def __len__(self): return self._list.__len__() # Not required. Makes printing behave like a list. def __repr__(self): return self._list.__repr__() Test it: In [34]: a = Super() In [35]: a Out[35]: [] In [36]: print a [] In [37]: len(a) Out[37]: 0 In [38]: a[0] --------------------------------------------------------------------------- IndexError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() /home/aaron/projects/test/test.py in __getitem__(self, index) 10 # Abstract method in Sequence, implemented in terms of list. 11 def __getitem__(self, index): ---> 12 return self._list.__getitem__(index) 13 14 # Abstract method in Sequence, implemented in terms of list. IndexError: list index out of range Just like a list. It's not abstract (for the moment) because we implemented both of Sequence's abstract methods. Now I want to add my bit of interface, which will be abstract in Super and therefore required to implement in any subclasses. And we'll cut to the chase and add subclasses that inherit from our ABC Super. from abc import abstractmethod from collections import Sequence class Super(Sequence): # Gives us a list member for ABC methods to use. def __init__(self): self._list = [] # Abstract method in Sequence, implemented in terms of list. def __getitem__(self, index): return self._list.__getitem__(index) # Abstract method in Sequence, implemented in terms of list. def __len__(self): return self._list.__len__() # Not required. Makes printing behave like a list. def __repr__(self): return self._list.__repr__() @abstractmethod def method1(): pass class Sub0(Super): pass class Sub1(Super): def __init__(self): self._list = [1, 2, 3] def method1(self): return [x**2 for x in self._list] def method2(self): return [x/2.0 for x in self._list] class Sub2(Super): def __init__(self): self._list = [10, 20, 30, 40] def method1(self): return [x+2 for x in self._list] We've added a new abstract method to Super, method1. This makes Super abstract again. A new class Sub0 which inherits from Super but does not implement method1, so it's also an ABC. Two new classes Sub1 and Sub2, which both inherit from Super. They both implement method1 from Super, so they're not abstract. Both implementations of method1 are different. Sub1 and Sub2 also both initialize themselves differently; in real life they might initialize themselves wildly differently. So you have two subclasses which both "is a" Super (they both implement Super's required interface) although their implementations are different. Also remember that Super, although an ABC, provides four non-abstract methods. So Super provides two things to subclasses: an implementation of collections.Sequence, and an additional abstract interface (the one abstract method) that subclasses must implement. Also, class Sub1 implements an additional method, method2, which is not part of Super's interface. Sub1 "is a" Super, but it also has additional capabilities. Test it: In [52]: a = Super() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Super with abstract methods method1 In [53]: a = Sub0() --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: Can't instantiate abstract class Sub0 with abstract methods method1 In [54]: a = Sub1() In [55]: a Out[55]: [1, 2, 3] In [56]: b = Sub2() In [57]: b Out[57]: [10, 20, 30, 40] In [58]: print a, b [1, 2, 3] [10, 20, 30, 40] In [59]: a, b Out[59]: ([1, 2, 3], [10, 20, 30, 40]) In [60]: a.method1() Out[60]: [1, 4, 9] In [61]: b.method1() Out[61]: [12, 22, 32, 42] In [62]: a.method2() Out[62]: [0.5, 1.0, 1.5] [63]: a[:2] Out[63]: [1, 2] In [64]: a[0] = 5 --------------------------------------------------------------------------- TypeError Traceback (most recent call last) /home/aaron/projects/test/<ipython console> in <module>() TypeError: 'Sub1' object does not support item assignment Super and Sub0 are abstract and can't be instantiated (lines 52 and 53). Sub1 and Sub2 are concrete and have an immutable Sequence interface (54 through 59). Sub1 and Sub2 are instantiated differently, and their method1 implementations are different (60, 61). Sub1 includes an additional method2, beyond what's required by Super (62). Any concrete Super acts like a list/Sequence (63). A collections.Sequence is immutable (64). Finally, a wart: In [65]: a._list Out[65]: [1, 2, 3] In [66]: a._list = [] In [67]: a Out[67]: [] Super._list is spelled with a single underscore. Double underscore would have protected it from this last bit, but would have broken the implementation of methods in subclasses. Not sure why; I think because double underscore is private, and private means private. So ultimately this whole scheme relies on a gentleman's agreement not to reach in and muck with Super._list directly, as in line 65 above. Would love to know if there's a safer way to do that.

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  • Foolishness Check: PHP Class finds Class file but not Class in the file.

    - by Daniel Bingham
    I'm at a loss here. I've defined an abstract superclass in one file and a subclass in another. I have required the super-classes file and the stack trace reports to find an include it. However, it then returns an error when it hits the 'extends' line: Fatal error: Class 'HTMLBuilder' not found in View/Markup/HTML/HTML4.01/HTML4_01Builder.php on line 7. I had this working with another class tree that uses factories a moment ago. I just added the builder layer in between the factories and the consumer. The factory layer looked almost exactly the same in terms of includes and dependencies. So that makes me think I must have done something silly that's causes the HTMLBuilder.php file to not be included correctly or interpreted correctly or some such. Here's the full stack trace (paths slightly altered): # Time Memory Function Location 1 0.0001 53904 {main}( ) ../index.php:0 2 0.0002 67600 require_once( 'View/Page.php' ) ../index.php:3 3 0.0003 75444 require_once( 'View/Sections/SectionFactory.php' ) ../Page.php:4 4 0.0003 81152 require_once( 'View/Sections/HTML/HTMLSectionFactory.php' ) ../SectionFactory.php:3 5 0.0004 92108 require_once( 'View/Sections/HTML/HTMLTitlebarSection.php' ) ../HTMLSectionFactory.php:5 6 0.0005 99716 require_once( 'View/Markup/HTML/HTMLBuilder.php' ) ../HTMLTitlebarSection.php:3 7 0.0005 103580 require_once( 'View/Markup/MarkupBuilder.php' ) ../HTMLBuilder.php:3 8 0.0006 124120 require_once( 'View/Markup/HTML/HTML4.01/HTML4_01Builder.php' ) ../MarkupBuilder.php:3 Here's the code in question: Parent class (View/Markup/HTML/HTMLBuilder.php): <?php require_once('View/Markup/MarkupBuilder.php'); abstract class HTMLBuilder extends MarkupBuilder { public abstract function getLink($text, $href); public abstract function getImage($src, $alt); public abstract function getDivision($id, array $classes=NULL, array $children=NULL); public abstract function getParagraph($text, array $classes=NULL, $id=NULL); } ?> Child Class, (View/Markup/HTML/HTML4.01/HTML4_01Builder.php): <?php require_once('HTML4_01Factory.php'); require_once('View/Markup/HTML/HTMLBuilder.php'); class HTML4_01Builder extends HTMLBuilder { private $factory; public function __construct() { $this->factory = new HTML4_01Factory(); } public function getLink($href, $text) { $link = $this->factory->getA(); $link->addAttribute('href', $href); $link->addChild($this->factory->getText($text)); return $link; } public function getImage($src, $alt) { $image = $this->factory->getImg(); $image->addAttribute('src', $src); $image->addAttribute('alt', $alt); return $image; } public function getDivision($id, array $classes=NULL, array $children=NULL) { $div = $this->factory->getDiv(); $div->setID($id); if(!empty($classes)) { $div->addClasses($classes); } if(!empty($children)) { $div->addChildren($children); } return $div; } public function getParagraph($text, array $classes=NULL, $id=NULL) { $p = $this->factory->getP(); $p->addChild($this->factory->getText($text)); if(!empty($classes)) { $p->addClasses($classes); } if(!empty($id)) { $p->setID($id); } return $p; } } ?> I would appreciate any and all ideas. I'm at a complete loss here as to what is going wrong. I'm sure it's something stupid I just can't see...

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  • Prefer class members or passing arguments between internal methods?

    - by geoffjentry
    Suppose within the private portion of a class there is a value which is utilized by multiple private methods. Do people prefer having this defined as a member variable for the class or passing it as an argument to each of the methods - and why? On one hand I could see an argument to be made that reducing state (ie member variables) in a class is generally a good thing, although if the same value is being repeatedly used throughout a class' methods it seems like that would be an ideal candidate for representation as state for the class to make the code visibly cleaner if nothing else. Edit: To clarify some of the comments/questions that were raised, I'm not talking about constants and this isn't relating to any particular case rather just a hypothetical that I was talking to some other people about. Ignoring the OOP angle for a moment, the particular use case that I had in mind was the following (assume pass by reference just to make the pseudocode cleaner) int x doSomething(x) doAnotherThing(x) doYetAnotherThing(x) doSomethingElse(x) So what I mean is that there's some variable that is common between multiple functions - in the case I had in mind it was due to chaining of smaller functions. In an OOP system, if these were all methods of a class (say due to refactoring via extracting methods from a large method), that variable could be passed around them all or it could be a class member.

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  • ctags doesn't work when class is defined like "class Gem::SystemExitException"

    - by dan
    You can define a class in a namespace like this class Gem class SystemExitException end end or class Gem::SystemExitException end When code uses first method of class definition, ctags indexes the class definition like this: SystemExitException test_class.rb /^ class SystemExitException$/;" c class:Gem With the second way, ctags indexes it like this: Gem rubygems/exceptions.rb /^class Gem::SystemExitException < SystemExit$/;" c The problem with the second way is that you can't put your cursor (in vim) over a reference to "Gem::SystemExitException" and have that jump straight to the class definition. Your only recourse is to page through all the (110!) class definitions that start with "Gem::" and find the one you're looking for. Does anyone know of a workaround? Maybe I should report this to the maintainer of ctags?

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  • Buddy List: Relational Database Table Design

    - by huntaub
    So, the modern concept of the buddy list: Let's say we have a table called Person. Now, that Person needs to have many buddies (of which each buddy is also in the person class). The most obvious way to construct a relationship would be through a join table. i.e. buddyID person1_id person2_id 0 1 2 1 3 6 But, when a user wants to see their buddy list, the program would have to check the column 'person1_id' and 'person2_id' to find all of their buddies. Is this the appropriate way to implement this kind of table, or would it be better to add the record twice.. i.e. buddyID person1_id person2_id 0 1 2 1 2 1 So that only one column has to be searched. Thanks in advance.

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  • Automatically generate buddy classes from model in C#

    - by JohnnyO
    I use Linq to Sql (although this is equally applicable in Entity Framework) for my models, and I'm finding myself creating buddy classes for my models all the time. I find this time consuming and repetitive. Is there an easy way to automatically generate these buddy classes based on the models? Perhaps a visual studio macro? An example of a buddy class that I'd like to create: [MetadataType(typeof(PersonMetadata))] public partial class Person { } public class PersonMetadata { public object Id { get; set; } public object FirstName { get; set; } } Thanks in advance.

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  • What control will be best for Buddy List?

    - by Arnab
    I'm developing a xmpp chat client in C#.NET. I'm little confused about what control should I use for Buddy list. Buddy list will consist of status icon, name & his buddy pic. Can u please recommend that what control will be best for me to use? (Do u think that ListView will be appropriate?) Another question, I'm using agsxmpp. Does it support invisible status in Gtalk. Is there any library out there bettre than this ? Thanks.

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  • Why do pure virtual base classes get direct access to static data members while derived instances do

    - by Shamster
    I've created a simple pair of classes. One is pure virtual with a static data member, and the other is derived from the base, as follows: #include <iostream> template <class T> class Base { public: Base (const T _member) { member = _member; } static T member; virtual void Print () const = 0; }; template <class T> T Base<T>::member; template <class T> void Base<T>::Print () const { std::cout << "Base: " << member << std::endl; } template <class T> class Derived : public Base<T> { public: Derived (const T _member) : Base<T>(_member) { } virtual void Print () const { std::cout << "Derived: " << this->member << std::endl; } }; I've found from this relationship that when I need access to the static data member in the base class, I can call it with direct access as if it were a regular, non-static class member. i.e. - the Base::Print() method does not require a this- modifier. However, the derived class does require the this-member indirect access syntax. I don't understand why this is. Both class methods are accessing the same static data, so why does the derived class need further specification? A simple call to test it is: int main () { Derived<double> dd (7.0); dd.Print(); return 0; } which prints the expected "Derived: 7"

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  • Class Plugins in PHP?

    - by YuriKolovsky
    i just got some more questions while learning PHP, does php implement any built in plugin system? so the plugin would be able to change the behavior of the core component. for example something like this works: include 'core.class.php'; include 'plugin1.class.php'; include 'plugin2.class.php'; new plugin2; where core.class.php contains class core { public function coremethod1(){ echo 'coremethod1'; } public function coremethod2(){ echo 'coremethod2'; } } plugin1.class.php contains class plugin1 extends core { public function coremethod1(){ echo 'plugin1method1'; } } plugin2.class.php contains class plugin2 extends plugin1 { public function coremethod2(){ echo 'plugin2method2'; } } This would be ideal, if not for the problem that now the plugins are dependable on each other, and removing one of the plugins: include 'core.class.php'; //include 'plugin1.class.php'; include 'plugin2.class.php'; new plugin2; breaks the whole thing... are there any proper methods to doing this? if there are not, them i might consider moving to a different langauge that supports this... thanks for any help.

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  • Interface vs Abstract Class (general OO)

    - by Kave
    Hi, I have had recently two telephone interviews where I've been asked about the differences between an Interface and an Abstract class. I have explained every aspect of them I could think of, but it seems they are waiting for me to mention something specific, and I dont know what it is. From my experience I think the following is true, if i am missing a major point please let me know: Interface: Every single Method declared in an Interface will have to be implemented in the subclass. Only Events, Delegates, Properties (C#) and Methods can exist in a Interface. A class can implement multiple Interfaces. Abstract Class Only Abstract methods have to be implemented by the subclass. An Abstract class can have normal methods with implementations. Abstract class can also have class variables beside Events, Delegates, Properties and Methods. A class can only implement one abstract class only due non-existence of Multi-inheritance in C#. 1) After all that the interviewer came up with the question What if you had an Abstract class with only abstract methods, how would that be different from an interface? I didnt know the answer but I think its the inheritance as mentioned above right? 2) An another interviewer asked me what if you had a Public variable inside the interface, how would that be different than in Abstract Class? I insisted you can't have a public variable inside an interface. I didn't know what he wanted to hear but he wasn't satisfied either. Many Thanks for clarification, Kave See Also: When to use an interface instead of an abstract class and vice versa Interfaces vs. Abstract Classes How do you decide between using an Abstract Class and an Interface?

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  • PHP Access property of a class from within a class instantiated in the original class.

    - by Iain
    I'm not certain how to explain this with the correct terms so maybe an example is the best method... $master = new MasterClass(); $master->doStuff(); class MasterClass { var $a; var $b; var $c; var $eventProccer; function MasterClass() { $this->a = 1; $this->eventProccer = new EventProcess(); } function printCurrent() { echo '<br>'.$this->a.'<br>'; } function doStuff() { $this->printCurrent(); $this->eventProccer->DoSomething(); $this->printCurrent(); } } class EventProcess { function EventProcess() {} function DoSomething() { // trying to access and change the parent class' a,b,c properties } } My problem is i'm not certain how to access the properties of the MasterClass from within the EventProcess-DoSomething() method? I would need to access, perform operations on and update the properties. The a,b,c properties will be quite large arrays and the DoSomething() method would be called many times during the execuction of the script. Any help or pointers would be much appreciated :)

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  • Why and when should I make a class 'static'? What is the purpose of 'static' keyword on classes?

    - by Saeed Neamati
    The static keyword on a member in many languages mean that you shouldn't create an instance of that class to be able to have access to that member. However, I don't see any justification to make an entire class static. Why and when should I make a class static? What benefits do I get from making a class static? I mean, after declaring a static class, one should still declare all members which he/she wants to have access to without instantiation, as static too. This means that for example, Math class could be declared normal (not static), without affecting how developers code. In other words, making a class static or normal is kind of transparent to developers.

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