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  • Why is it a good practice to wrap all primitives and Strings?

    - by Amogh Talpallikar
    According to Jeff Bay's Essay on Object Callisthenics, One of the practices is set to be "Wrap all primitives and Strings" Can anyone elaborate on this ? In languages where we already have wrappers for primitives like C# and Java. and In languages where Collections can have generics where you are sure of what type goes into the collection, do we need to wrap string's inside their own classes ? Does it have any other advantage ?

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  • Designing application flow

    - by Umesh Awasthi
    I am creating a web application in java where I need to mock the following flow. When user trigger a certain process (add product to cart), I need to pass through following steps Need to see in HTTP Session if user is logged in. Check HTTP Session if shopping cart is there If user exist in HTTP Session and his/her cart do not exist in HTTP Session Get user cart from the database. add item to cart and save it to HTTP session and update cart in DB. If cart does not exist in DB, create new cart and and save in it HTTP Session. Though I missed a lot of use cases here (do not want question length to increase a lot), but most of the flow will be same as I described in above steps. My flow will start from the Controller and will go towards Service Layer and than ends up in the DAO layer. Since there will be a lot of use cases where I need to check HTTP session and based on that need to call Service layer, I was planning to add a Facade layer which should be responsible to do this for me like checking Session and interacting with Service layer. Please suggest if this is a valid approach or any other best approach can be implemented here? One more point where I am confused is how to handle HTTP session in facade layer? do I need to pass HTTP session object each time I call my Facade or any other approach can be used here?

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  • Best practice to propagate preferences of application

    - by Shebuka
    What is your approach with propagation to all classes/windows of preferences/settings of your application? Do you share the preference_manager class to all classes/windows who need it or you make variables in each classes/windows and update them manually each time setting are changed? Currently I have a PreferencesInterface class that hold all preferences and is responsible to default all values with a dedicated method called on create and when needed, all values are public, so non getters/setters, also it have virtual SavePreferences/LoadPreferences methods. Then I have PreferencesManager that extends from PreferencesInterface and is responsible for actually implementation of SavePreferences/LoadPreferences. I've made this basically for cross-platform so that every platform can have a different implementation of actual storage (registry, ini, plist, xml, whatever).

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  • How do you think about an Application Generator? [closed]

    - by Mehdi Sheyda
    I'm designing an application-generating application. It is an application that takes the requirements of customer as inputs , analyzes the requirements, creates classes and produces program files in C#. I am at the beginning of this project and have a long way to go with this application. Do you have an experience with designing similar kinds of projects? What risks might I encounter with this project?

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  • Please help me give this principle a name

    - by Brent Arias
    As a designer, I like providing interfaces that cater to a power/simplicity balance. For example, I think the LINQ designers followed that principle because they offered both dot-notation and query-notation. The first is more powerful, but the second is easier to read and follow. If you disagree with my assessment of LINQ, please try to see my point anyway; LINQ was just an example, my post is not about LINQ. I call this principle "dial-able power". But I'd like to know what other people call it. Certainly some will say "KISS" is the common term. But I see KISS as a superset, or a "consumerism" practice. Using LINQ as my example again, in my view, a team of programmers who always try to use query notation over dot-notation are practicing KISS. Thus the LINQ designers practiced "dial-able power", whereas the LINQ consumers practice KISS. The two make beautiful music together. I'll give another example. Imagine a C# logging tool that has two signatures allowing two uses: void Write(string message); void Write(Func<string> messageCallback); The purpose of the two signatures is to fulfill these needs: //Every-day "simple" usage, nothing special. myLogger.Write("Something Happened" + error.ToString() ); //This is performance critical, do not call ToString() if logging is //disabled. myLogger.Write( () => { "Something Happened" + error.ToString() }); Having these overloads represents "dial-able power," because the consumer has the choice of a simple interface or a powerful interface. A KISS-loving consumer will use the simpler signature most of the time, and will allow the "busy" looking signature when the power is needed. This also helps self-documentation, because usage of the powerful signature tells the reader that the code is performance critical. If the logger had only the powerful signature, then there would be no "dial-able power." So this comes full-circle. I'm happy to keep my own "dial-able power" coinage if none yet exists, but I can't help think I'm missing an obvious designation for this practice. p.s. Another example that is related, but is not the same as "dial-able power", is Scott Meyer's principle "make interfaces easy to use correctly, and hard to use incorrectly."

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  • DDD: Service or Repository

    - by tikhop
    I am developing an app in DDD manner. And I have a little problem with it. I have a Fare (airline fare) and FareRepository objects. And at some point I should load additional fare information and set this information to existing Fare. I guess that I need to create an Application Service (FareAdditionalInformationService) that will deal with obtaining data from the server and than update existing Fare. However, some people said me that it is necessary to use FareRepository for this problem. I don't know wich place is better for my problem Service or Repository.

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  • Should each app have its own database, or should small apps be merged into one?

    - by King
    We have a bunch of small to medium sized apps, each of which has its own database (MSSQL Server). There was a suggestion that we consoldate the 'related' databases into a smaller set amount of larger databases. They don't particularly share a lot of data, they would just be under a similar business group. For example, using a 'Finance' DB to hold the tables and procedures for finance apps. Would it be appropriate to use a different schema for each app? E.g. App1.SomeTable App1.SomeOtherTable AppTwo.SomeTable What are the pros and cons of this approach? What should I watch out for? Thanks

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  • Is it a good practice to wrap all primitives and Strings?

    - by Amogh Talpallikar
    According to Jeff Bay's Essay on Object Callisthenics, One of the practices is set to be "Wrap all primitives and Strings" Can anyone elaborate on this ? In languages where we already have wrappers for primitives like C# and Java. and In languages where Collections can have generics where you are sure of what type goes into the collection, do we need to wrap string's inside their own classes ? Does it have any other advantage ?

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  • Single database, multiple system dependency

    - by davenewza
    Consider an environment where we have a single, core database, with many separate systems using this one database. This leads to all of these systems have a common dependency, which ultimately introduces coupling between them. This means that we cannot always evolve systems independently of each other. Structural changes to the database (even if only intended for one, particular system), requires a full sweep test of ALL systems, and may require that other systems be 'patched' and subsequently released. This is especially tricky when you want to have separate teams working on different projects. What is a good 'pattern' to help in avoiding such coupling? I would imagine that a database should be exclusively depended on by one system. If other systems require data for whatever reason, they should request such from an API service of some kind. A drawback of this approach which comes to mind is performance: routing data between high-throughput systems through service calls is much slower than through a database connection.

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  • Manager/Container class vs static class methods

    - by Ben
    Suppose I a have a Widget class that is part of a framework used independently by many applications. I create Widget instances in many situations and their lifetimes vary. In addition to Widget's instance specified methods, I would like to be able to perform the follow class wide operations: Find a single Widget instance based on a unique id Iterate over the list of all Widgets Remove a widget from the set of all widgets In order support these operations, I have been considering two approaches: Container class - Create some container or manager class, WidgetContainer, which holds a list of all Widget instances, support iteration and provides methods for Widget addition, removal and lookup. For example in C#: public class WidgetContainer : IEnumerable<Widget { public void AddWidget(Widget); public Widget GetWidget(WidgetId id); public void RemoveWidget(WidgetId id); } Static class methods - Add static class methods to Widget. For example: public class Widget { public Widget(WidgetId id); public static Widget GetWidget(WidgetId id); public static void RemoveWidget(WidgetId id); public static IEnumerable<Widget AllWidgets(); } Using a container class has the added problem of how to access the container class. Make it a singleton?..yuck! Create some World object that provides access to all such container classes? I have seen many frameworks that use the container class approach, so what is the general consensus?

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  • How to create a fountain in UDK

    - by user36425
    I'm trying to make a fountain in my level in UDK, I made the base of the fountain by using a Cylinder build and now I'm trying to put water in it. I went to use the fluidSurfaceActor but I notice that this is square but my fountain is a cylinder. Is there a way that I can change the shape of the fluidSurfaceActor to fit the builder brush shape or is there another way to do this? Or is it hopeless and I have to make my fountain into a cube? Here is a link/picture to the screenprint of what I'm talking about:

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  • My boss has a different idea of a website's UX [migrated]

    - by NicoJuicy
    Let me explain the situation. I started transforming a "old (.Net 2.0)" Application into a webapplication. Problem here is, that no-one here is really acquainted with the UX of a website (Simple, efficient). Eventhough, i still have to regard that the website can be tailored to a customer needs through parameters (yeah, i know :s ) For example: I wanted to have a layout similar to invoicemachine (= as simple as possible). -- He wants a Ribbon toolbar. Going to a supplier gives the list of supplier -- He wants to display the "Create Supplier" screen where you can use the wildcards in a certain textbox, to search for a specific Supplier and then give the list of the suppliers. Also, i need 4 search/filter mechanisms: people can search per field with wildmarks can filter the suppliers search a keyword through all the data of a supplier filter the "list Suppliers" page by the first letter of the name. LIST Suppliers | A | D | Z Adam Wrincle ADD |EDIT |Delete Damzel InDistress ADD |EDIT |Delete Zorro ADD |EDIT |Delete I can't seem to get through to him, that the UX of a website needs to be differently than a Windows Application. If he wants to bring all the logic of the windows app into a website, why letting me build a website then? Stick to the old solution. Am i mistaking so hard or how could i convince / show him that an online-solution is something different than the offline solution. He already "saw" online solutions of other applications to get an idea, but if i suggest something he won't listen (if it's GUI / UX related, that is).

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  • Patterns for Handling Changing Property Sets in C++

    - by Bhargav Bhat
    I have a bunch "Property Sets" (which are simple structs containing POD members). I'd like to modify these property sets (eg: add a new member) at run time so that the definition of the property sets can be externalized and the code itself can be re-used with multiple versions/types of property sets with minimal/no changes. For example, a property set could look like this: struct PropSetA { bool activeFlag; int processingCount; /* snip few other such fields*/ }; But instead of setting its definition in stone at compile time, I'd like to create it dynamically at run time. Something like: class PropSet propSetA; propSetA("activeFlag",true); //overloading the function call operator propSetA("processingCount",0); And the code dependent on the property sets (possibly in some other library) will use the data like so: bool actvFlag = propSet["activeFlag"]; if(actvFlag == true) { //Do Stuff } The current implementation behind all of this is as follows: class PropValue { public: // Variant like class for holding multiple data-types // overloaded Conversion operator. Eg: operator bool() { return (baseType == BOOLEAN) ? this->ToBoolean() : false; } // And a method to create PropValues various base datatypes static FromBool(bool baseValue); }; class PropSet { public: // overloaded[] operator for adding properties void operator()(std::string propName, bool propVal) { propMap.insert(std::make_pair(propName, PropVal::FromBool(propVal))); } protected: // the property map std::map<std::string, PropValue> propMap; }; This problem at hand is similar to this question on SO and the current approach (described above) is based on this answer. But as noted over at SO this is more of a hack than a proper solution. The fundamental issues that I have with this approach are as follows: Extending this for supporting new types will require significant code change. At the bare minimum overloaded operators need to be extended to support the new type. Supporting complex properties (eg: struct containing struct) is tricky. Supporting a reference mechanism (needed for an optimization of not duplicating identical property sets) is tricky. This also applies to supporting pointers and multi-dimensional arrays in general. Are there any known patterns for dealing with this scenario? Essentially, I'm looking for the equivalent of the visitor pattern, but for extending class properties rather than methods. Edit: Modified problem statement for clarity and added some more code from current implementation.

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  • How do I choose the scaling factor of a 3D game world?

    - by concept3d
    I am making a 3D tank game prototype with some physics simulation, am using C++. One of the decisions I need to make is the scale of the game world in relation to reality. For example, I could consider 1 in-game unit of measurement to correspond to 1 meter in reality. This feels intuitive, but I feel like I might be missing something. I can think of the following as potential problems: 3D modelling program compatibility. (?) Numerical accuracy. (Does this matter?) Especially at large scales, how games like Battlefield have huge maps: How don't they lose numerical accuracy if they use 1:1 mapping with real world scale, since floating point representation tend to lose more precision with larger numbers (e.g. with ray casting, physics simulation)? Gameplay. I don't want the movement of units to feel slow or fast while using almost real world values like -9.8 m/s^2 for gravity. (This might be subjective.) Is it ok to scale up/down imported assets or it's best fit with a world with its original scale? Rendering performance. Are large meshes with the same vertex count slower to render? I'm wondering if I should split this into multiple questions...

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  • How can one manage thousands of IF...THEN...ELSE rules?

    - by David
    I am considering building an application, which, at its core, would consist of thousands of if...then...else statements. The purpose of the application is to be able to predict how cows move around in any landscape. They are affected by things like the sun, wind, food source, sudden events etc. How can such an application be managed? I imagine that after a few hundred IF-statements, it would be as good as unpredictable how the program would react and debugging what lead to a certain reaction would mean that one would have to traverse the whole IF-statement tree every time. I have read a bit about rules engines, but I do not see how they would get around this complexity.

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  • Understanding Visitor Pattern

    - by Nezreli
    I have a hierarchy of classes that represents GUI controls. Something like this: Control-ContainerControl-Form I have to implement a series of algoritms that work with objects doing various stuff and I'm thinking that Visitor pattern would be the cleanest solution. Let take for example an algorithm which creates a Xml representaion of a hierarchy of objects. Using 'classic' approach I would do this: public abstract class Control { public virtual XmlElement ToXML(XmlDocument document) { XmlElement xml = document.CreateElement(this.GetType().Name); // Create element, fill it with attributes declared with control return xml; } } public abstract class ContainerControl : Control { public override XmlElement ToXML(XmlDocument document) { XmlElement xml = base.ToXML(document); // Use forech to fill XmlElement with child XmlElements return xml; } } public class Form : ContainerControl { public override XmlElement ToXML(XmlDocument document) { XmlElement xml = base.ToXML(document); // Fill remaining elements declared in Form class return xml; } } But I'm not sure how to do this with visitor pattern. This is the basic implementation: public class ToXmlVisitor : IVisitor { public void Visit(Form form) { } } Since even the abstract classes help with implementation I'm not sure how to do that properly in ToXmlVisitor. Perhaps there is a better solution to this problem. The reason that I'm considering Visitor pattern is that some algorithms will need references not available in project where the classes are implemented and there is a number of different algorithms so I'm avoiding large classes. Any thoughts are welcome.

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  • Resources for popular domain models

    - by Songo
    I have come across many situations where I had to build a system for a library or a clinic or other popular domains. The thing is a domain model for a library was probably done 1000 times already with different level of details of course. Here is an example. Is there a popular website or community where one can find ready made domain models for popular systems? The whole purpose I'm trying to achieve is to quickly get a grasp of the domain I'm modeling and customize it to my needs. Re-inventing the wheel seems really absurd when the same system might have been modeled properly previously. Note I know Google might sound like the perfect source, but there is a repository out there that people can post there models, so that others can share them.

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  • DDD and filtering

    - by tikhop
    I am developing an app in ddd maner. So I have a complex domain model. Suppose I have a Fare object and Airline. Each Airline should contain several or much more Fares. My UI should represent Model (only small part of complex model) as a list of Airline, when the user select the Airline, I must show the list of Fares. User can filtering the Fares (by travel time, cost, etc.). What is the appropriate place for filtering Fares and Airlines? I am assuming that I should do it in ViewModel. Like: My domain model has wrapped with Service Layer - UI works with ViewModel - ViewModel obtain data from Service Layer filtering it and create DTO objects for UI. Or I'm wrong?

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  • Liskov substitution and abstract classes / strategy pattern

    - by Kolyunya
    I'm trying to follow LSP in practical programming. And I wonder if different constructors of subclasses violate it. It would be great to hear an explanation instead of just yes/no. Thanks much! P.S. If the answer is no, how do I make different strategies with different input without violating LSP? class IStrategy { public: virtual void use() = 0; }; class FooStrategy : public IStrategy { public: FooStrategy(A a, B b) { c = /* some operations with a, b */ } virtual void use() { std::cout << c; } private: C c; }; class BarStrategy : public IStrategy { public: BarStrategy(D d, E e) { f = /* some operations with d, e */ } virtual void use() { std::cout << f; } private: F f; };

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  • How to use DI and DI containers

    - by Pinetree
    I am building a small PHP mvc framework (yes, yet another one), mostly for learning purposes, and I am trying to do it the right way, so I'd like to use a DI container, but I am not asking which one to use but rather how to use one. Without going into too much detail, the mvc is divided into modules which have controllers which render views for actions. This is how a request is processed: a Main object instantiates a Request object, and a Router, and injects the Request into the Router to figure out which module was called. then it instantiates the Module object and sends the Request to that the Module creates a ModuleRouter and sends the Request to figure out the controller and action it then creates the Controller and the ViewRenderer, and injects the ViewRenderer into the Controller (so that the controller can send data to the view) the ViewRenderer needs to know which module, controller and action were called to figure out the path to the view scripts, so the Module has to figure out this and inject it to the ViewRenderer the Module then calls the action method on the controller and calls the render method on the ViewRenderer For now, I do not have any DI container set up, but what I do have are a bunch of initX() methods that create the required component if it is not already there. For instance, the Module has the initViewRenderer() method. These init methods get called right before that component is needed, not before, and if the component was already set it will not initialize it. This allows for the components to be switched, but it does not require manually setting them if they are not there. Now, I'd like to do this by implementing a DI container, but still keep the manual configuration to a bare minimum, so if the directory structure and naming convention is followed, everything should work, without even touching the config. If I use the DI container, do I then inject it into everything (the container would inject itself when creating a component), so that other components can use it? When do I register components with the DI? Can a component register other components with the DI during run-time? Do I create a 'common' config and use that? How do I then figure out on the fly which components I need and how they need to be set up? If Main uses Router which uses Request, Main then needs to use the container to get Module (or does the module need to be found and set beforehand? How?) Module uses Router but needs to figure out the settings for the ViewRenderer and the Controller on the fly, not in advance, so my DI container can't be setting those on the Module before the module figures out the controller and action... What if the controller needs some other service? Do I inject the container into every controller? If I start doing that, I might just inject it into everything... Basically I am looking for the best practices when dealing with stuff like this. I know what DI is and what DI containers do, but I am looking for guidance to using them in real life, and not some isolated examples on the net. Sorry for the lengthy post and many thanks in advance.

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  • creating a pre-menu level select screen

    - by Ephiras
    Hi I am working on creating a tower Defence java applet game and have come to a road block about implementing a title screen that i can select the level and difficulty of the rest of the game. my title screen class is called Menu. from this menu class i need to pass in many different variables into my Main class. i have used different classes before and know how to run them and such. but if both classes extend applet and each has its individual graphics method how can i run things from Main even though it was created in Menu. what i essentially want to do is run the Menu class withits action listeners and graphics until a Difficulty button has been selected, run the main class (which 100% works without having to have the Menu class) and pretty much terminate Menu so that i cannot go back to it, do not see its buttons or graphics menus. can i run one applet annd when i choose a button close that one and launch the other one? IF you would like to download the full project you can find it here, i had to comment out all the code that wasn't working my Menu class import java.awt.*; import java.awt.event.*; import java.applet.*; public class Menu extends Applet implements ActionListener{ Button bEasy,bMed,bHard; Main m; public void init(){ bEasy= new Button("Easy"); bEasy.setBounds(140,200,100,50); add(bEasy); bMed = new Button("Medium");bMed.setBounds(280,200,100,50); add(bMed); bHard= new Button("Hard");bHard.setBounds(420,200,100,50); add(bHard); setLayout(null); } public void actionPerformed(ActionEvent e){ Main m = new Main(20,10,3000,mapMed);//break; switch (e.getSource()){ case bEasy: Main m = new Main(6000,20,"levels/levelEasy.png");break;//enimies tower money world case bMed: Main m = new Main(4000,15,"levels/levelMed.png");break; case bHard: Main m = new Main(2000,10,"levels/levelEasy.png");break; default: break; } } public void paint(){ //m.draw(g) } } and here is my main class initialising code. import java.awt.*; import java.awt.event.*; import java.applet.*; import java.io.IOException; public class Main extends Applet implements Runnable, MouseListener, MouseMotionListener, ActionListener{ Button startButton, UpgRange, UpgDamage; //set up the buttons Color roadCol,startCol,finCol,selGrass,selRoad; //set up the colors Enemy e[][]; Tower t[]; Image towerpic,backpic,roadpic,levelPic; private Image i; private Graphics doubleG; //here is the world 0=grass 1=road 2=start 3=end int world[][],eStartX,eStartY; boolean drawMouse,gameEnd; static boolean start=false; static int gridLength=15; static int round=0; int Mx,My,timer=1500; static int sqrSize=31; int towers=0,towerSelected=-10; static int castleHealth=2000; String levelPath; //choose the level Easy Med or Hard int maxEnemy[] = {5,7,12,20,30,15,50,30,40,60};//number of enimies per round int maxTowers=15;//maximum number of towers allowed static int money =2000,damPrice=600,ranPrice=350,towerPrice=700; //money = the intial ammount of money you start of with //damPrice is the price to increase the damage of a tower //ranPrice is the price to increase the range of a tower public void main(int cH,int mT,int mo,int dP,int rP,int tP,String path,int[] mE)//constructor 1 castleHealth=cH; maxTowers=mT; money=mo; damPrice=dP; ranPrice=rP; towerPrice=tP; String levelPath=path; maxEnemy = mE; buildLevel(); } public void main(int cH,int mT,String path)//basic constructor castleHealth=cH; maxTowers=mT; String levelPath=path; maxEnemy = mE; buildLevel(); } public void init(){ setSize(sqrSize*15+200,sqrSize*15);//set the size of the screen roadCol = new Color(255,216,0);//set the colors for the different objects startCol = new Color(0,38,255); finCol = new Color(255,0,0); selRoad = new Color(242,204,155);//selColor is the color of something when your mouse hovers over it selGrass = new Color(0,190,0); roadpic = getImage(getDocumentBase(),"images/road.jpg"); towerpic = getImage(getDocumentBase(),"images/tower.png"); backpic = getImage(getDocumentBase(),"images/grass.jpg"); levelPic = getImage(getDocumentBase(),"images/level.jpg"); e= new Enemy[maxEnemy.length][];//activates all of the enimies for (int r=0;r<e.length;r++) e[r] = new Enemy[maxEnemy[r]]; t= new Tower[maxTowers]; for (int i=0;i<t.length;i++) t[i]= new Tower();//activates all the towers for (int i=0;i<e.length; i++)//sets all of the enimies starting co ordinates for (int j=0;j<e[i].length;j++) e[i][j] = new Enemy(eStartX,eStartY,world); initButtons();//initialise all the buttons addMouseMotionListener(this); addMouseListener(this); }

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  • How to present a stable data model in a public API that allows internal data structures to be changed without breaking the public view of the data?

    - by Max Palmer
    I am in the process of developing an application that allows users to write C# scripts. These scripts allow users to call selected methods and to access and manipulate data in a document. This works well, however, in the development version, scripts access the document's (internal) data structures directly. This means that if we were to change the internal data model/structure, there is a good chance that someone's script will no longer compile. We obviously want to prevent this breaking change from happening, but still want to allow the user to write sensible C# code (whilst not restricting how we develop our internal data model as a result). We therefore need to decouple our scripting API and its data structures from our internal methods and data structures. We've a few ideas as to how we might allow the user to access a what is effectively a stable public version of the document's internal data*, but I wanted to throw the question out there to someone who might have some real experience of this problem. NB our internal document's data structure is quite complex and it could be quite difficult to wrap. We know we want to expose as little as possible in our public API, especially as once it's out there, it's out there for good. Can anyone help? How do scripting languages / APIs decouple their public API and data structures from their internal data structures? Is there no real alternative to having to write a complex interaction layer? If we need to do this, what's a good approach or pattern for wrapping complex data structures that include nested objects, including collections? I've looked at the API facade pattern, which looks like it's trying to address these kinds of issues, but are there alternatives? *One idea is to build a data facade that is kept stable across versions of our application. The facade exposes a set of facade data objects that are used in the script code. These maintain backwards compatibility and wrap access to our internal document's data model.

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  • Is loose coupling w/o use cases an anti-pattern?

    - by dsimcha
    Loose coupling is, to some developers, the holy grail of well-engineered software. It's certainly a good thing when it makes code more flexible in the face of changes that are likely to occur in the foreseeable future, or avoids code duplication. On the other hand, efforts to loosely couple components increase the amount of indirection in a program, thus increasing its complexity, often making it more difficult to understand and often making it less efficient. Do you consider a focus on loose coupling without any use cases for the loose coupling (such as avoiding code duplication or planning for changes that are likely to occur in the foreseeable future) to be an anti-pattern? Can loose coupling fall under the umbrella of YAGNI?

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  • What are other ideologies to establish relationships between distinct users besides followers/following and friends?

    - by user784637
    Websites like myspace and facebook establish relationships between distinct users using the "friending" ideology, where one user sends a request to be accepted by another user in order for them to have the mutual permission to do stuff like post messages on each others walls. Less restrictive than the "friending" ideology, Twitter and instagram use the followers/following ideology where you can subscribe to the tweets or posts of another user without their permission. Less restrictive than the "followers/following" ideology, email and calling someone on the phone allows you to directly contact anyone. Are there other ideologies that have been successfully implemented either in social networking sites or other real world constructs to establish relations between users?

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  • Rails: Law of Demeter Confusion

    - by user2158382
    I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. EDIT I completely understand and agree that this is still a violation and I need to create a method in Wallet called withdraw that handles the payment for me and that I should call that method inside the Customer class. What I don't get is that according to this process, my first example still violates the Law of Demeter because Invoice is still reaching directly into Customer to get the street. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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