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  • What are your thoughts on Raven DB?

    - by Ronnie Overby
    What are your thoughts on Raven DB? I see this below my title: The question you're asking appears subjective and is likely to be closed. Please don't do that. I think the question is legit because: Raven DB is brand-spanking-new. RDBMS's are probably the de facto for data persistence for .net developers, which Raven DB is not. Given these points, I would like to know your general opinions. Admittedly, the question is sort of broad. That is intentional, because I am trying to learn as much about it as possible, however here are some of my initial concerns and questions: What about using Raven DB for data storage in a shared web hosting environment, since Raven DB is interacted with through HTTP? Are there any areas that Raven DB is particularly well or not well suited for? How does it rank among alternatives, from a .net developer's perspective?

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  • OOP Design of items in a Point-of-Sale system

    - by Jonas
    I am implementing a Point-of-Sale system. In the system I represent an Item in three places, and I wounder how I should represent them in OOP. First I have the WarehouseItem, that contains price, purchase price, info about the supplier, suppliers price, info about the product and quantity in warehouse. Then I have CartItem, which contains the same fields as WarehouseItem, but adds NrOfItems and Discount. And finally I have ReceiptItem, thats contains an item where I have stripped of info about the supplier, and only contains the price that was payed. Are there any OOP-recommendations, best-practices or design patterns that I could apply for this? I don't really know if CartItem should contain (wrap) an WarehouseItem, or extend it, or if I just should copy the fields that I need. Maybe I should create an Item-class where I keep all common fields, and then extend it to WarehouseItem, CartItem and ReceiptItem. Sometimes I think that it is good to keep the field of the item and just display the information that is needed.

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  • Concrete Types or Interfaces for return types?

    - by SDReyes
    Today I came to a fundamental paradox of the object programming style, concrete types or interfaces. Whats the better election for a method's return type: a concrete type or an interface? In most cases, I tend to use concrete types as the return type for methods. because I believe that an concrete type is more flexible for further use and exposes more functionality. The dark side of this: Coupling. The angelic one: A concrete type contains per-se the interface you would going to return initially, and extra functionality. What's your thumb's rule? Is there any programming principle for this? BONUS: This is an example of what I mean http://stackoverflow.com/questions/491375/readonlycollection-or-ienumerable-for-exposing-member-collections

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  • Best practices for class-mapping with SoapClient

    - by Foofy
    Using SoapClient's class mapping feature and it's pretty sweet. Unfortunately the SOAP service we're using has a bunch of read-only properties on some of the objects and will throw faults if the properties are passed back as anything but null. Need to filter out the properties before they're used in the SOAP call and am looking for advice on the best way to do it. So far the options are: Stick to a convention where I use getter and setter functions to manipulate the properties, and use property overloading to filter method access since only SoapClient would be doing that. E.g. developers would access properties like this: $obj->getAccountNumber() SoapClient would access properties like this: $obj->accountNumber I don't like this because the properties are still exposed and things could go wrong if developers don't stick to convention. Have a wrapper for SoapClient that sets a public property the mapped objects can check to see if the property is being accessed by SoapClient. I already have a wrapper that assigns a reference to itself to all the mapped objects. class SoapClientWrapper { public function __soapCall($method, $args) { $this->setSoapMode(true); $this->_soapClient->__soapCall($method, $args); $this->setSoapMode(false); } } class Invoice { function __get($val) { if($this->_soapClient->getSoapMode()) { return null; } else { return $this->$val; } } } This works but it doesn't feel right and seems a bit clunky. Do the mapping manually, and don't use SoapClient's mapping features. I'd just have a function on all the mapped objects that returns the safe-to-send properties. Also, nobody would have access to properties they shouldn't since I could enforce getters and setters. A lot more work, though.

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  • Correct OOP design without getters?

    - by kane77
    I recently read that getters/setters are evil and I have to say it makes sense, yet when I started learning OOP one of the first things I learned was "Encapsulate your fields" so I learned to create class give it some fields, create getters, setters for them and create constructor where I initialize these fields. And every time some other class needs to manipulate this object (or for instance display it) I pass it the object and it manipulate it using getters/setters. I can see problems with this approach. But how to do it right? For instance displaying/rendering object that is "data" class - let's say Person, that has name and date of birth. Should the class have method for displaying the object where some Renderer would be passed as an argument? Wouldn't that violate principle that class should have only one purpose (in this case store state) so it should not care about presentation of this object. Can you suggest some good resources where best practices in OOP design are presented? I'm planning to start a project in my spare time and I want it to be my learning project in correct OOP design..

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  • A PHP design pattern for the model part [PHP Zend Framework]

    - by Matthieu
    I have a PHP MVC application using Zend Framework. As presented in the quickstart, I use 3 layers for the model part : Model (business logic) Data mapper Table data gateway (or data access object, i.e. one class per SQL table) The model is UML designed and totally independent of the DB. My problem is : I can't have multiple instances of the same "instance/record". For example : if I get, for example, the user "Chuck Norris" with id=5, this will create a new model instance wich members will be filled by the data mapper (the data mapper query the table data gateway that query the DB). Then, if I change the name to "Duck Norras", don't save it in DB right away, and re-load the same user in another variable, I have "synchronisation" problems... (different instances for the same "record") Right now, I use the Multiton pattern : like Singleton, but multiple instances indexed by a key (wich is the user ID in our example). But this is complicating my developpement a lot, and my testings too. How to do it right ?

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  • Design pattern for parsing data that will be grouped to two different ways and flipped

    - by lewisblackfan
    I'm looking for an easily maintainable and extendable design model for a script to parse an excel workbook into two separate workbooks after pulling data from other locations like the command line, and a database. The high level details are as follows. I need to parse an excel workbook containing a sheet that lists unique question names, the only reliable information that can be parsed from the question name is the book code that identifies the title and edition of the textbook the question is associated with, the rest of the question name is not standardized well enough to be reliably parsed by computer. The general form of the question name is best described by the following regular expression. '^(\w+)\s(\w{1,2})\.(\w{1,2})\.(\w{1,3})\.(\w{1,3}\.)*$' The first sub-pattern is the book code, the second sub-pattern is 90% of the time the chapter, and the rest of the sub-patterns could be section, problem type, problem number, or question type information. There is no simple logic, at least not one I can find. There will be a minimum of three other columns in this spreadsheet; one column will be the chapter the question is associated with, the second will be the section within the chapter the question is associated with, and the third will be some kind of asset indicated by a uniform resource locator. 1 | 1 | qname1 | url | description | url | description ... 1 | 1 | qname2 | url | description 1 | 1 | qname3 | url | description | url | description | url | The asset can be indicated by a full or partial uniform resource locator, the partial url will need to be completed before it can be fed into the application. There theoretically could be no limit to the number of asset columns, the assets will be grouped in columns by type. Some times additional data will have to be retrieved from a database or combined with the book code before the asset url is complete and can be understood by the application that will be using the asset. The type is an abstraction, there are eight types right now, each with their own logic in how the uniform resource locator is handled and or completed, and I have to add a new type and its logic every three or four months. For each asset url there is the possibility of a description column, a character string for display in the application, but not always. (I've already worked out validating the description text, and squashing MSs obscure code page down to something 7-bit ascii can handle.) Now that all the details are filled-in I can get to the actual problem of parsing the file. I need to split the information in this excel workbook into two separate workbooks. The first workbook will group all the questions by section in rows. With the first cell being the section doublet and the rest of the cells in the row are the question names. 1.1 | qname1 | qname2 | qname3 | qname4 | 1.2 | qname1 | qname2 | qname3 | 1.3 | qname1 | qname2 | qname3 | qname4 | qname5 There is no set number of questions for each section as you can see from the above example. The second workbook is more complicated, there is one row per asset, and question names that have more than one asset will be duplicated. There will be four or five columns on this sheet. The first is the question name for the asset, the second is a media type used to select the correct icon for the asset in the application, the third is string representing the asset type, the four is the full and complete uniform resource locator for the asset, and the fifth columns is the optional text description for the asset. q1 | mtype1 | atype1 | url | description q1 | mtype2 | atype2 | url | description q1 | mtype2 | atype3 | url | description q2 | mtype1 | atype1 | url | description q2 | mtype2 | atype3 | url | description For the original six types I did have a script that parsed the source excel workbook into the other two excel workbooks, and I was able to add two more types until I ran aground on the implementation of the ninth type and tenth types. What broke my script was the fact that the ninth type is actually a sub-type of one of the original six, but with entirely different logic, and my mostly procedural script could not accommodate without duplicating a lot of code. I also had a lot of bugs in the script and will be writing the test first on this time around. I'm stuck with the format for the resulting two workbooks, this script is glue code, development went ahead with the project without bothering to get a complete spec from the sponsor. I work for the same company as the developers but in the editorial department, editorial is co-sponsor of the project, and am expected to fix pesky details like this (I'm foaming at the mouth as I type this). I've tried factories, I've tried different object models, but each resulting workbook is so different when I find a design that works for generating one workbook the code is not really usable for generating the other. What I would really like are ideas about a maintainable and extensible design for parsing the source workbook into both workbooks with maximum code reuse, and or sympathy.

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  • Create Class functions on the fly?

    - by JasonS
    Hi, i have a validation class which needs improving. If I require some custom validation I need to specify a custom function. It works a bit like this: The controller tells the validation that a custom validation function is required. The controller runs the validation. --- Gets iffy here --- Validation class creates a new instance of the controller class.... Validation class runs controller-custom_validation_function() Validation class returns true / false Is there someway that I can alter this to do something like this? $validation = new validation; // Insert rules here. $validation-function() = $this-function(); By doing this I could get rid of the step of creating an unneeded class instance.

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  • When writing a game, should you make objects/enemies/etc. have unique ID numbers?

    - by SLC
    I have recently encountered some issues with merely passing references to objects/enemies in a game I am making, and am wondering if I am using the wrong approach. The main issue I have is disposing of enemies and objects, when other enemies or players may still have links to them. For example, if you have a Rabbit, and a Wolf, the Wolf may have selected the Rabbit to be its target. What I am doing, is the wolf has a GameObject Target = null; and when it decides it is hungry, the Target becomes the Rabbit. If the Rabbit then dies, such as another wolf killing it, it cannot be removed from the game properly because this wolf still has a reference to it. In addition, if you are using a decoupled approach, the rabbit could hit by lightning, reducing its health to below zero. When it next updates itself, it realises it has died, and is removed from the game... but there is no way to update everything that is interested in it. If you gave every enemy a unique ID, you could simply use references to that instead, and use a central lookup class that handled it. If the monster died, the lookup class could remove it from its own index, and subsequently anything trying to access it would be informed that it's dead, and then they could act accordingly. Any thoughts on this?

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  • Proper way to set class variables

    - by ensnare
    I'm writing a class to insert users into a database, and before I get too far in, I just want to make sure that my OO approach is clean: class User(object): def setName(self,name): #Do sanity checks on name self._name = name def setPassword(self,password): #Check password length > 6 characters #Encrypt to md5 self._password = password def commit(self): #Commit to database >>u = User() >>u.setName('Jason Martinez') >>u.setPassword('linebreak') >>u.commit() Is this the right approach? Should I declare class variables up top? Should I use a _ in front of all the class variables to make them private? Thanks for helping out.

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  • Suggestions for Single-Page Web Application Design?

    - by DaveDev
    My view is that unless you need to change the basic structure of the user interface, you should not have to reload the page at all for any user interactions. I'd like to approach my next ASP.NET MVC project with this in mind. Can anyone suggest any principles, patterns or practices* I should consider? Excellent book, btw. Still trying to wrap my head around some of the concepts though. I thought a question like this would help link the theory to a practical design. Thanks

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  • Object database for website

    - by Damian
    I was planning to use db4o for a website. It's a microblog site with small posts and comments developed in java. The thing is I contacted db4o support asking if db4o would be suitable for a website, and they answered me that only for websites with low concurrency. That means with few requests? So, now I think db4o will not be a good choice. Do you know if there is any object database for java suitable for a website?

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  • Implementation of a general-purpose object structure (property bag)

    - by Thomas Wanner
    We need to implement some general-purpose object structure, much like an object in dynamic languages, that would give us a possibility of creating the whole object graph on-the-fly. This class has to be serializable and somehow user friendly. So far we have made some experiments with class derived from Dictionary<string, object> using the dot notation path to store properties and collections in the object tree. We have also find an article that implements something similar, but it doesn't seem to fit completely into our picture either. Do you know about some good implementations / libraries that deal with a similar problem or do you have any (non-trivial) ideas that could help us with our own implementation ? Also, I probably have to say that we are using .NET 3.5, so we can't take advantage of the new features in .NET 4.0 like dynamic type etc. (as far as I know it's also not possible to use any subset of it in .NET 3.5 solution).

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  • How to structure a Genetic Algorithm class hierarchy?

    - by MahlerFive
    I'm doing some work with Genetic Algorithms and want to write my own GA classes. Since a GA can have different ways of doing selection, mutation, cross-over, generating an initial population, calculating fitness, and terminating the algorithm, I need a way to plug in different combinations of these. My initial approach was to have an abstract class that had all of these methods defined as pure virtual, and any concrete class would have to implement them. If I want to try out two GAs that are the same but with different cross-over methods for example, I would have to make an abstract class that inherits from GeneticAlgorithm and implements all the methods except the cross-over method, then two concrete classes that inherit from this class and only implement the cross-over method. The downside to this is that every time I want to swap out a method or two to try out something new I have to make one or more new classes. Is there another approach that might apply better to this problem?

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  • USE case to Class Diagram - How do I?

    - by 01010011
    Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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  • ASIHTTPRequest code design

    - by nico
    I'm using ASIHTTPRequest to communicate with the server asynchronously. It works great, but I'm doing requests in different controllers and now duplicated methods are in all those controllers. What is the best way to abstract that code (requests) in a single class, so I can easily re-use the code, so I can keep the controllers more simple. I can put it in a singleton (or in the app delegate), but I don't think that's a good approach. Or maybe make my own protocol for it with delegate callback. Any advice on a good design approach would be helpful. Thanks.

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  • Adding functionality to any TextReader

    - by strager
    I have a Location class which represents a location somewhere in a stream. (The class isn't coupled to any specific stream.) The location information will be used to match tokens to location in the input in my parser, to allow for nicer error reporting to the user. I want to add location tracking to a TextReader instance. This way, while reading tokens, I can grab the location (which is updated by the TextReader as data is read) and give it to the token during the tokenization process. I am looking for a good approach on accomplishing this goal. I have come up with several designs. Manual location tracking Every time I need to read from the TextReader, I call AdvanceString on the Location object of the tokenizer with the data read. Advantages Very simple. No class bloat. No need to rewrite the TextReader methods. Disadvantages Couples location tracking logic to tokenization process. Easy to forget to track something (though unit testing helps with this). Bloats existing code. Plain TextReader wrapper Create a LocatedTextReaderWrapper class which surrounds each method call, tracking a Location property. Example: public class LocatedTextReaderWrapper : TextReader { private TextReader source; public Location Location { get; set; } public LocatedTextReaderWrapper(TextReader source) : this(source, new Location()) { } public LocatedTextReaderWrapper(TextReader source, Location location) { this.Location = location; this.source = source; } public override int Read(char[] buffer, int index, int count) { int ret = this.source.Read(buffer, index, count); if(ret >= 0) { this.location.AdvanceString(string.Concat(buffer.Skip(index).Take(count))); } return ret; } // etc. } Advantages Tokenization doesn't know about Location tracking. Disadvantages User needs to create and dispose a LocatedTextReaderWrapper instance, in addition to their TextReader instance. Doesn't allow different types of tracking or different location trackers to be added without layers of wrappers. Event-based TextReader wrapper Like LocatedTextReaderWrapper, but decouples it from the Location object raising an event whenever data is read. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. Can have multiple, independent Location objects (or other methods of tracking) tracking at once. Disadvantages Requires boilerplate code to enable location tracking. User needs to create and dispose the wrapper instance, in addition to their TextReader instance. Aspect-orientated approach Use AOP to perform like the event-based wrapper approach. Advantages Can be reused for other types of tracking. Tokenization doesn't know about Location tracking or other tracking. No need to rewrite the TextReader methods. Disadvantages Requires external dependencies, which I want to avoid. I am looking for the best approach in my situation. I would like to: Not bloat the tokenizer methods with location tracking. Not require heavy initialization in user code. Not have any/much boilerplate/duplicated code. (Perhaps) not couple the TextReader with the Location class. Any insight into this problem and possible solutions or adjustments are welcome. Thanks! (For those who want a specific question: What is the best way to wrap the functionality of a TextReader?) I have implemented the "Plain TextReader wrapper" and "Event-based TextReader wrapper" approaches and am displeased with both, for reasons mentioned in their disadvantages.

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  • Is the design notion of layers contrived?

    - by Bruce
    Hi all I'm reading through Eric Evans' awesome work, Domain-Driven Design. However, I can't help feeling that the 'layers' model is contrived. To expand on that statement, it seems as if it tries to shoe-horn various concepts into a specific, neat model, that of layers talking to each other. It seems to me that the layers model is too simplified to actually capture the way that (good) software works. To expand further: Evans says: "Partition a complex program into layers. Develop a design within each layer that is cohesive and that depends only on the layers below. Follow standard architectural patterns to provide loose coupling to the layers above." Maybe I'm misunderstanding what 'depends' means, but as far as I can see, it can either mean a) Class X (in the UI for example) has a reference to a concrete class Y (in the main application) or b) Class X has a reference to a class Y-ish object providing class Y-ish services (ie a reference held as an interface). If it means (a), then this is clearly a bad thing, since it defeats re-using the UI as a front-end to some other application that provides Y-ish functionality. But if it means (b), then how is the UI any more dependent on the application, than the application is dependent on the UI? Both are decoupled from each other as much as they can be while still talking to each other. Evans' layer model of dependencies going one way seems too neat. First, isn't it more accurate to say that each area of the design provides a module that is pretty much an island to itself, and that ideally all communication is through interfaces, in a contract-driven/responsibility-driven paradigm? (ie, the 'dependency only on lower layers' is contrived). Likewise with the domain layer talking to the database - the domain layer is as decoupled (through DAO etc) from the database as the database is from the domain layer. Neither is dependent on the other, both can be swapped out. Second, the idea of a conceptual straight line (as in from one layer to the next) is artificial - isn't there more a network of intercommunicating but separate modules, including external services, utility services and so on, branching off at different angles? Thanks all - hoping that your responses can clarify my understanding on this..

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  • XAML Binding to complex value objects

    - by Gus
    I have a complex value object class that has 1) a number or read-only properties; 2) a private constructor; and 3) a number of static singleton instance properties [so the properties of a ComplexValueObject never change and an individual value is instantiated once in the application's lifecycle]. public class ComplexValueClass { /* A number of read only properties */ private readonly string _propertyOne; public string PropertyOne { get { return _propertyOne; } } private readonly string _propertyTwo; public string PropertyTwo { get { return _propertyTwo; } } /* a private constructor */ private ComplexValueClass(string propertyOne, string propertyTwo) { _propertyOne = propertyOne; _propertyTwo = PropertyTwo; } /* a number of singleton instances */ private static ComplexValueClass _complexValueObjectOne; public static ComplexValueClass ComplexValueObjectOne { get { if (_complexValueObjectOne == null) { _complexValueObjectOne = new ComplexValueClass("string one", "string two"); } return _complexValueObjectOne; } } private static ComplexValueClass _complexValueObjectTwo; public static ComplexValueClass ComplexValueObjectTwo { get { if (_complexValueObjectTwo == null) { _complexValueObjectTwo = new ComplexValueClass("string three", "string four"); } return _complexValueObjectTwo; } } } I have a data context class that looks something like this: public class DataContextClass : INotifyPropertyChanged { private ComplexValueClass _complexValueClass; public ComplexValueClass ComplexValueObject { get { return _complexValueClass; } set { _complexValueClass = value; PropertyChanged(this, new PropertyChangedEventArgs("ComplexValueObject")); } } } I would like to write a XAML binding statement to a property on my complex value object that updates the UI whenever the entire complex value object changes. What is the best and/or most concise way of doing this? I have something like: <Object Value="{Binding ComplexValueObject.PropertyOne}" /> but the UI does not update when ComplexValueObject as a whole changes.

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  • Attribute References in Python

    - by Jeune
    I do Java programming and recently started learning Python via the official documentation. I see that we can dynamically add data attributes to an instance object unlike in Java: class House: pass my_house = House() my_house.number = 40 my_house.rooms = 8 my_house.garden = 1 My question is, in what situations is this feature used? What are the advantages and disadvantages compared to the way it is done in Java?

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  • Are ORM's counterproductive to OO design?

    - by Jeremiah
    In OOD, design of an object is said to be characterized by its identity and behavior. Having used OR/M's in the past, the primary purpose, in my opinion, revolves around the ability to store/retrieve data. That is to say, OR/M objects are not design by behavior, but rather data (i.e. database tables). Case and point: Many OR/M tools come with a point-to-a-database-table-and-click-object-generator. If objects are no longer characterized by behavior this will, in my opinion, muddy the identity and responsibility of the objects. Subsequently, if objects are not defined by a responsibility this could lend a hand to having tightly coupled classes and overall poor design. Furthermore, I would think that in an application setting, you would be heading towards scalability issues. So, my question is, do you think that ORM's are counterproductive to OO design? Perhaps the underlying question would be whether or not they are counterproductive to application development.

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  • Wrappers/law of demeter seems to be an anti-pattern...

    - by Robert Fraser
    I've been reading up on this "Law of Demeter" thing, and it (and pure "wrapper" classes in general) seem to generally be anti patterns. Consider an implementation class: class Foo { void doSomething() { /* whatever */ } } Now consider two different implementations of another class: class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething() { _foo.doSomething(); } } And the ways to call said methods: callingMethod() { Bar1.getFoo().doSomething(); // Version 1 Bar2.doSomething(); // Version 2 } At first blush, version 1 seems a bit simpler, and follows the "rule of Demeter", hide Foo's implementation, etc, etc. But this ties any changes in Foo to Bar. For example, if a parameter is added to doSomething, then we have: class Foo { void doSomething(int x) { /* whatever */ } } class Bar1 { private static Foo _foo = new Foo(); public static Foo getFoo() { return _foo; } } class Bar2 { private static Foo _foo = new Foo(); public static void doSomething(int x) { _foo.doSomething(x); } } callingMethod() { Bar1.getFoo().doSomething(5); // Version 1 Bar2.doSomething(5); // Version 2 } In both versions, Foo and callingMethod need to be changed, but in Version 2, Bar also needs to be changed. Can someone explain the advantage of having a wrapper/facade (with the exception of adapters or wrapping an external API or exposing an internal one).

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  • looking for automated modeling tool for ASP.Net class diagramming

    - by alchemical
    I'm walking into a project with 500+ classes, and am wondering if anyone has had good experiences with automated modeling tools that can import from ASP.Net /C#? It would be a bonus if I could get an automated model based on all the objects called to completely load a single ASP.Net page, with relationships indicating which objects are calling out to which other ones, etc. Thanks for sharing your thoughts or recomendations.

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