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  • Compiler doesn't find methods from base class

    - by Paul
    I am having a problem with my virtual methods in a derived class. Here are my (simplified) C++ classes. class Base virtual method accept( MyVisitor1* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; virtual method accept( MyVisitor3* v ) { /*implementation is here*/ }; class DerivedClass virtual method accept( MyVisitor2* v ) { /*implementation is here*/ }; The following use causes VS 2005 to give: "error C2664: 'DerivedClass::accept' : cannot convert parameter 1 from 'Visitor1*' to 'Visitor2 *'". DerivedClass c; MyVisitor1 v1; c.accept(v1); I was expecting the compiler to find and call Base::accept(MyVisitor1) for my DerivedClass as well. Obviously this is not working, but I don't understand why. Any ideas? Thanks, Paul

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  • Logging *Business* Events - use logging framework?

    - by UpTheCreek
    Hi, Something here doesn't feel right to me here, and so I would like the community's input - perhaps I am approaching this in the wrong way.... Q: Is is appropriate to use traditional infrastructure logging frameworks (like log4net) to log business events? When I say business events, I mean I want a global log like this: xx:xx Customer A purchased widget B. xx:xx Widget B was dispatched from warehouse. xx:xx Customer B payment declined. Most traditional infrastructure logging frameworks have event levels something like this: FATAL ERROR WARN INFO DEBUG An of course these messages don't fit well into that. Best description would be INFO, but of course these are important events, and INFO is of very low importance. I would still like this as a 'log' (e.g. I don't want to have to extract this from my business objects each time I want to see it) Seems to me I have two options: 1) Use a framework like log4net and just define a special logger for this (and live with the fact that it doesn't feel right). 2) Provide a service for performing this that doesn't rely on a traditional logging services. I'm leaning towards 2. What has anyone else done in a similar situations? Thanks!

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  • How to leverage Spring Integration in a real-world JMS distributed architecture?

    - by ngeek
    For the following scenario I am looking for your advices and tips on best practices: In a distributed (mainly Java-based) system with: many (different) client applications (web-app, command-line tools, REST API) a central JMS message broker (currently in favor of using ActiveMQ) multiple stand-alone processing nodes (running on multiple remote machines, computing expensive operations of different types as specified by the JMS message payload) How would one best apply the JMS support provided by the Spring Integration framework to decouple the clients from the worker nodes? When reading through the reference documentation and some very first experiments it looks like the configuration of an JMS inbound adapter inherently require to use a subscriber, which in a decoupled scenario does not exist. Small side note: communication should happen via JMS text messages (using a JSON data structure for future extensibility).

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  • How can I make a family of singletons?

    - by Jay
    I want to create a set of classes that share a lot of common behavior. Of course in OOP when you think that you automatically think "abstract class with subclasses". But among the things I want these classes to do is to each have a static list of instances of the class. The list should function as sort of a singleton within the class. I mean each of the sub-classes has a singleton, not that they share one. "Singleton" to that subclass, not a true singleton. But if it's a static, how can I inherit it? Of course code like this won't work: public abstract A { static List<A> myList; public static List getList() { if (myList==null) myList=new ArrayList<A>(10); return myList; } public static A getSomethingFromList() { List listInstance=getList(); ... do stuff with list ... } public int getSomethingFromA() { ... regular code acting against current instance ... } } public class A1 extends A { ... } public class A2 extends A { ... } A1 somethingfromA1List=(A1) A1.getSomethingFromList(); A2 somethingfromA2List=(A2) A2.getSomethingFromList(); The contents of the list for each subclass would be different, but all the code to work on the lists would be the same. The problem with the above code is that I'd only have one list for all the subclasses, and I want one for each. Yes, I could replicate the code to declare the static list in each of the subclasses, but then I'd also have to replicate all the code that adds to the lists and searches the list, etc, which rather defeats the purpose of subclassing. Any ideas on how to do this without replicating code?

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  • Immutability of big objects

    - by Malax
    Hi StackOverflow! I have some big (more than 3 fields) Objects which can and should be immutable. Every time I run into that case i tend to create constructor abominations with long parameter lists. It doesn't feel right, is hard to use and readability suffers. It is even worse if the fields are some sort of collection type like lists. A simple addSibling(S s) would ease the object creation so much but renders the object mutable. What do you guys use in such cases? I'm on Scala and Java, but i think the problem is language agnostic as long as the language is object oriented. Solutions I can think of: "Constructor abominations with long parameter lists" The Builder Pattern Thanks for your input!

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  • Risking the exception anti-pattern.. with some modifications

    - by Sridhar Iyer
    Lets say that I have a library which runs 24x7 on certain machines. Even if the code is rock solid, a hardware fault can sooner or later trigger an exception. I would like to have some sort of failsafe in position for events like this. One approach would be to write wrapper functions that encapsulate each api a: returnCode=DEFAULT; try { returnCode=libraryAPI1(); } catch(...) { returnCode=BAD; } return returnCode; The caller of the library then restarts the whole thread, reinitializes the module if the returnCode is bad. Things CAN go horribly wrong. E.g. if the try block(or libraryAPI1()) had: func1(); char *x=malloc(1000); func2(); if func2() throws an exception, x will never be freed. On a similar vein, file corruption is a possible outcome. Could you please tell me what other things can possibly go wrong in this scenario?

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  • Avoid loading unnecessary data from db into objects (web pages)

    - by GmGr
    Really newbie question coming up. Is there a standard (or good) way to deal with not needing all of the information that a database table contains loaded into every associated object. I'm thinking in the context of web pages where you're only going to use the objects to build a single page rather than an application with longer lived objects. For example, lets say you have an Article table containing id, title, author, date, summary and fullContents fields. You don't need the fullContents to be loaded into the associated objects if you're just showing a page containing a list of articles with their summaries. On the other hand if you're displaying a specific article you might want every field loaded for that one article and maybe just the titles for the other articles (e.g. for display in a recent articles sidebar). Some techniques I can think of: Don't worry about it, just load everything from the database every time. Have several different, possibly inherited, classes for each table and create the appropriate one for the situation (e.g. SummaryArticle, FullArticle). Use one class but set unused properties to null at creation if that field is not needed and be careful. Give the objects access to the database so they can load some fields on demand. Something else? All of the above seem to have fairly major disadvantages. I'm fairly new to programming, very new to OOP and totally new to databases so I might be completely missing the obvious answer here. :)

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  • Singleton Pattern combine with a Decorator

    - by Mike
    Attached is a classic Decorator pattern. My question is how would you modify the below code so that you can wrap zero or one of each topping on to the Pizza Right now I can have a Pepporini - Sausage -- Pepporini -- Pizza class driving the total cost up to $10, charging twice for Pepporini. I don't think I want to use the Chain of Responsibility pattern as order does not matter and not all toppings are used? Thank you namespace PizzaDecorator { public interface IPizza { double CalculateCost(); } public class Pizza: IPizza { public Pizza() { } public double CalculateCost() { return 8.00; } } public abstract class Topping : IPizza { protected IPizza _pizzaItem; public Topping(IPizza pizzaItem) { this._pizzaItem = pizzaItem; } public abstract double CalculateCost(); } public class Pepporini : Topping { public Pepporini(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 0.50; } } public class Sausage : Topping { public Sausage(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + 1.00; } } public class Onions : Topping { public Onions(IPizza pizzaItem) : base(pizzaItem) { } public override double CalculateCost() { return this._pizzaItem.CalculateCost() + .25; } } }

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  • Data Modeling Help - Do I add another table, change existing table's usage, or something else?

    - by StackOverflowNewbie
    Assume I have the following tables and relationships: Person - Id (PK) - Name A Person can have 0 or more pets: Pet - Id (PK) - PersonId (FK) - Name A person can have 0 or more attributes (e.g. age, height, weight): PersonAttribute _ Id (PK) - PersonId (FK) - Name - Value PROBLEM: I need to represent pet attributes, too. As it turns out, these pet attributes are, in most cases, identical to the attributes of a person (e.g. a pet can have an age, height, and weight too). How do I represent pet attributes? Do I create a PetAttribute table? PetAttribute Id (PK) PetId (FK) Name Value Do I change PersonAttribute to GenericAttribute and have 2 foreign keys in it - one connecting to Person, the other connecting to Pet? GenericAttribute Id (PK) PersonId (FK) PetId (FK) Name Value NOTE: if PersonId is set, then PetId is not set. If PetId is set, PersonId is not set. Do something else?

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  • Haskell: "how much" of a type should functions receive? and avoiding complete "reconstruction"

    - by L01man
    I've got these data types: data PointPlus = PointPlus { coords :: Point , velocity :: Vector } deriving (Eq) data BodyGeo = BodyGeo { pointPlus :: PointPlus , size :: Point } deriving (Eq) data Body = Body { geo :: BodyGeo , pict :: Color } deriving (Eq) It's the base datatype for characters, enemies, objects, etc. in my game (well, I just have two rectangles as the player and the ground right now :p). When a key, the characters moves right, left or jumps by changing its velocity. Moving is done by adding the velocity to the coords. Currently, it's written as follows: move (PointPlus (x, y) (xi, yi)) = PointPlus (x + xi, y + yi) (xi, yi) I'm just taking the PointPlus part of my Body and not the entire Body, otherwise it would be: move (Body (BodyGeo (PointPlus (x, y) (xi, yi)) wh) col) = (Body (BodyGeo (PointPlus (x + xi, y + yi) (xi, yi)) wh) col) Is the first version of move better? Anyway, if move only changes PointPlus, there must be another function that calls it inside a new Body. I explain: there's a function update which is called to update the game state; it is passed the current game state, a single Body for now, and returns the updated Body. update (Body (BodyGeo (PointPlus xy (xi, yi)) wh) pict) = (Body (BodyGeo (move (PointPlus xy (xi, yi))) wh) pict) That tickles me. Everything is kept the same within Body except the PointPlus. Is there a way to avoid this complete "reconstruction" by hand? Like in: update body = backInBody $ move $ pointPlus body Without having to define backInBody, of course.

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  • Truly declarative language?

    - by gjvdkamp
    Hi all, Does anyone know of a truly declarative language? The behaviour I'm looking for is kind of what Excel does, where I can define variables and formulas, and have the formula's result change when the input changes (without having set the answer again myself) The behaviour I'm looking for is best shown with this pseudo code: X = 10 // define and assign two variables Y = 20; Z = X + Y // declare a formula that uses these two variables X = 50 // change one of the input variables ?Z // asking for Z should now give 70 (50 + 20) I've tried this in a lot of languages like F#, python, matlab etc, but every time i try this they come up with 30 instead of 70. Wich is correct from an imperative point of view, but i'm looking for a more declerative behaviour if you know what i mean. And this is just a very simple calculation. When things get more difficult it should handle stuff like recursion and memoization automagically. The code below would obviously work in C# but it's just so much code for the job, i'm looking for something a bit more to the point without all that 'technical noise' class BlaBla{ public int X {get;set;} // this used to be even worse before 3.0 public int Y {get;set;} public int Z {get{return X + Y;}} } static void main(){ BlaBla bla = new BlaBla(); bla.X = 10; bla.Y = 20; // can't define anything here bla.X = 50; // bit pointless here but I'll do it anyway. Console.Writeline(bla.Z);// 70, hurray! } This just seems like so much code, curly braces and semicolons that add nothing. Is there a language/ application (apart from Exel) that does this? Maybe I'm no doing it right in the mentioned langauges, or I've completely missed an app that does just this. I prototyped a language/ application that does this (along with some other stuff) and am thinking of productizing it. I just can't believe it's not there yet. Don't want to waste my time. Thanks in advance, Gert-Jan

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  • PHP: Best solution for links breaking in a mod_rewrite app

    - by psil
    I'm using mod rewrite to redirect all requests targeting non-existent files/directories to index.php?url=* This is surely the most common thing you do with mod_rewrite yet I have a problem: Naturally, if the page url is "mydomain.com/blog/view/1", the browser will look for images, stylesheets and relative links in the "virtual" directory "mydomain.com/blog/view/". Problem 1: Is using the base tag the best solution? I see that none of the PHP frameworks out there use the base tag, though. I'm currently having a regex replace all the relative links to point to the right path before output. Is that "okay"? Problem 2: It is possible that the server doesn't support mod_rewrite. However, all public files like images, stylesheets and the requests collector index.php are located in the directory /myapp/public. Normally mod_rewrite points all request to /public so it seems as if public was actually the root directory too all users. However if there is no mod_rewrite, I then have to point the users to /public from the root directory with a header() call. That means, however that all links are broken again because suddenly all images, etc. have to be called via /public/myimage.jpg Additional info: When there is no mod_rewrite the above request would look like this: mydomain.com/public/index.php/blog/view/1 What would be the best solutions for both problems?

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  • Need alternative field names for these reserved words

    - by MattSlay
    “type” and “class” are likely reserved or problematic words in C# and/or Ruby, two languages I may use to program against my new database schema in the future. So, in order to avoid potential conflicts with those languages, I’m looking for alternative names for these field names in my tables. In this case, it is from my Machines table, where I have: “class” field (values would be something like “manual” or “computerized”) and “type” field (values would be “lathe” or “mill”) I could call the fields “machineclass” and “machinetype”, but that is inconsistent with naming scheme in the rest of my schema (meaning, I do not re-use the table name in the field… For instance, I use Machine.name, not Machine.machinename) Any thought on this madness?

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  • MVC pattern implementation. What is the n-relation between its components

    - by Srodriguez
    Dear all, I'm working in a C# project and we are , in order to get some unity across the different parts of our UI, trying to use the MVC pattern. The client is windows form based and I'm trying to create a simple MVC pattern implementation. It's been more challenging than expected, but I still have some questions regarding the MVC pattern. The problem comes mostly from the n-n relationships between its components: Here is what I've understood, but I'm not sure at all of it. Maybe someone can correct me? Model: can be shared among different Views. 1-n relationship between Model-View View: shows the state of the model. only one controller (can be shared among different views?). 1-1 relationship with the Model, 1-1 relationship with the controller Controller: handles the user actions on the view and updates the model. One controller can be shared among different views, a controller interacts only with one model? I'm not sure about the two last ones: Can a view have several controller? Or can a view share a controller with another view? Or is it only a 1:1 relationship? Can a controller handle several views? can it interact with several models? Also, I take advantage of this question to ask another MVC related question. I've suppressed all the synchronous calls between the different members of the MVC, making use of the events and delegates. One last call is still synchronous and is actually the most important one: The call between the view and the controller is still synchronous, as I need to know rather the controller has been able to handle the user's action or not. This is very bad as it means that I could block the UI thread (hence the client itself) while the controller is processing or doing some work. How can I avoid this? I can make use of the callback but then how do i know to which event the callback comes from? PS: I can't change the pattern at this stage, so please avoid answers of type "use MVP or MVVC, etc ;) Thanks!

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  • MVC pattern implementation. What is the n-relation between its components

    - by Srodriguez
    Dear all, I'm working in a C# project and we are , in order to get some unity across the different parts of our UI, trying to use the MVC pattern. The client is windows form based and I'm trying to create a simple MVC pattern implementation. It's been more challenging than expected, but I still have some questions regarding the MVC pattern. The problem comes mostly from the n-n relationships between its components: Here is what I've understood, but I'm not sure at all of it. Maybe someone can correct me? Model: can be shared among different Views. 1-n relationship between Model-View View: shows the state of the model. only one controller (can be shared among different views?). 1-1 relationship with the Model, 1-1 relationship with the controller Controller: handles the user actions on the view and updates the model. One controller can be shared among different views, a controller interacts only with one model? I'm not sure about the two last ones: Can a view have several controller? Or can a view share a controller with another view? Or is it only a 1:1 relationship? Can a controller handle several views? can it interact with several models? Also, I take advantage of this question to ask another MVC related question. I've suppressed all the synchronous calls between the different members of the MVC, making use of the events and delegates. One last call is still synchronous and is actually the most important one: The call between the view and the controller is still synchronous, as I need to know rather the controller has been able to handle the user's action or not. This is very bad as it means that I could block the UI thread (hence the client itself) while the controller is processing or doing some work. How can I avoid this? I can make use of the callback but then how do i know to which event the callback comes from? PS: I can't change the pattern at this stage, so please avoid answers of type "use MVP or MVVC, etc ;) Thanks!

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  • Rails Full Engine using a Full Engine

    - by SirLenz0rlot
    I've got this full rails engine Foo with functionality X. I want to make another engine, engine Bar, that is pretty much the same, but override funcitonality x with y. (it basically does the same, but a few controller actions and views are differently implemented). (I might split this later in several mountable engines, but for now, this will be the setup: project Baz, using engine Bar, which uses engine Foo) I would like to know if there are any pitfalls. It doesn't seem like a pattern that is often used? Anybody else using this 'some sort of engine inheritance'?

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  • CSS box around box technique

    - by webzide
    Dear Experts, I was trying to make an CSS division box with content in it as well as a border around it. Instead of using the box-border technique, I was trying out a new box to box technique instead. <html> <head> <style type="text/css"> #outer{ height: 20px; width: 20px; background-color:#233D78; } #inner{ height:18px; width: 18px; background-color: #FFF; font-size: 1em; text-align:center; font-family:'Bookman Old Style', serif; padding: 0px; margin-top: 1px; margin-right:auto; margin-left:auto; margin-bottom:1px; vertical-align:middle; } </style> </head> <body> <div id="outer"><div id="inner">TEXT</div></div> </body> </html> Somehow the borders are just not showing up right with FireFox. I tried everything. Setting up the Paddings of both boxes, margin, and messing around with the width. TO be honest, it took me around 30min to do this and I still can't get it right :( I know that a way to achieve the same result would be setting up a border around just one box. But I just wanna learn this box around box background-color technique. THanks in advance

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  • C#: How to inherit constructors?

    - by Ian Boyd
    Imagine a base class with many constructors and a virtual method public class Foo { ... public Foo() {...} public Foo(int i) {...} ... public virtual void SomethingElse() {...} ... } and now I want to create a descendant class that overrides the virtual method: public class Bar : Foo { public override void SomethingElse() {...} } And another descendant that does some more stuff: public class Bah : Bar { public void DoMoreStuff() {...} } Do I really have to copy all constructors from Foo into Bar and Bah? And then if I change a constructor signature in Foo, do I have to update it in Bar and Bah? Is there no way to inherit constructors? Is there no way to encourage code reuse?

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  • smallest mysql type that accomodates single decimal

    - by donpal
    Database newbie here. I'm setting up a mysql table. One of the fields will accept a value in increment of a 0.5. e.g. 0.5, 1.0, 1.5, 2.0, .... 200.5, etc. I've tried int but it doesn't capture the decimals. `value` int(10), What would be the smallest type that can accommodate this value, considering it's only a single decimal. I also was considering that because the decimal will always be 0.5 if at all, I could store it in a separate boolean field? So I would have 2 fields instead. Is this a stupid or somewhat over complicated idea? I don't know if it really saves me any memory, and it might get slower now that I'm accessing 2 fields instead of 1 `value` int(10), `half` bool, //or something similar to boolean What are your suggestions guys? Is the first option better, and what's the smallest data type in that case that would get me the 0.5?

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  • Generalized plugable caching pattern?

    - by BCS
    Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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  • Method hiding with interfaces

    - by fearofawhackplanet
    interface IFoo { int MyReadOnlyVar { get; } } class Foo : IFoo { int MyReadOnlyVar { get; set; } } public IFoo GetFoo() { return new Foo { MyReadOnlyVar = 1 }; } Is the above an acceptable way of implementing a readonly/immutable object? The immutability of IFoo can be broken with a temporary cast to Foo. In general (non-critical) cases, is hiding functionality through interfaces a common pattern? Or is it considered lazy coding? Or even an anti-pattern?

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  • How should I use color in my application? Single, Theme, or Chaos?

    - by CodeSlave
    How should I be using color in my application? I have over a 100 different forms (windows) in my application, and the default windows grey seems like a bad choice to me. One school of thought says pick one neutral color, and use the same one everywhere. Another school of thought says pick a set of neutral colors, and use them same ones within a group of form (e.g., shipping screens might be light green, receiving screens light orange, user administration screens light blue, etc.). The final school of thought says make every form different. We've got millions of colors, why not use them? What should I do and why?

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  • Where should I put contextual data related to an Object that is not really a property of the object?

    - by RenderIn
    I have a Car class. It has three properties: id, color and model. In a particular query I want to return all the cars and their properties, and I also want to return a true/false field called "searcherKnowsOwner" which is a field I calculate in my database query based on whether or not the individual conducting the search knows the owner. I have a database function that takes the ID of the searcher and the ID of the car and returns a boolean. My car class looks like this (pseudocode): class Car{ int id; Color color; Model model; } I have a screen where I want to display all the cars, but I also want to display a flag next to each car if the person viewing the page knows the owner of that car. Should I add a field to the Car class, a boolean searcherKnowsOwner? It's not a property of the car, but is actually a property of the user conducting the search. But this seems like the most efficient place to put this information.

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