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  • Using free function as pseudo-constructors to exploit template parameter deduction

    - by Poita_
    Is it a common pattern/idiom to use free functions as pseudo-constructors to avoid having to explicitly specify template parameters? For example, everyone knows about std::make_pair, which uses its parameters to deduce the pair types: template <class A, class B> std::pair<A, B> make_pair(A a, B b) { return std::pair<A, B>(a, b); } // This allows you to call make_pair(1, 2), // instead of having to type pair<int, int>(1, 2) // as you can't get type deduction from the constructor. I find myself using this quite often, so I was just wondering if many other people use it, and if there is a name for this pattern?

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  • Recommendations for an in memory database vs thread safe data structures

    - by yx
    TLDR: What are the pros/cons of using an in-memory database vs locks and concurrent data structures? I am currently working on an application that has many (possibly remote) displays that collect live data from multiple data sources and renders them on screen in real time. One of the other developers have suggested the use of an in memory database instead of doing it the standard way our other systems behaves, which is to use concurrent hashmaps, queues, arrays, and other objects to store the graphical objects and handling them safely with locks if necessary. His argument is that the DB will lessen the need to worry about concurrency since it will handle read/write locks automatically, and also the DB will offer an easier way to structure the data into as many tables as we need instead of having create hashmaps of hashmaps of lists, etc and keeping track of it all. I do not have much DB experience myself so I am asking fellow SO users what experiences they have had and what are the pros & cons of inserting the DB into the system?

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  • Three level database - foreign keys

    - by poke
    I have a three level database with the following structure (simplified to only show the primary keys): Table A: a_id Table B: a_id, b_id Table C: a_id, b_id, c_id So possible values for table C would be something like this: a_id b_id c_id 1 1 1 1 1 2 1 1 3 1 2 1 1 2 2 2 1 1 2 2 1 2 2 2 ... I am now unsure, how foreign keys should be set; or if they should be set for the primary keys at all. My idea was to have a foreign key on table B B.a_id -> A.a_id, and two foreign key on C C.a_id -> A.a_id and ( C.a_id, C.b_id ) -> ( B.a_id, B.b_id ). Is that the way I should set up the foreign keys? Is the foreign key from C->A necessary? Or do I even need foreign keys at all given that all those columns are part of the primary keys? Thanks.

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  • Android ignoring my setWidth() and setHeight()

    - by popoffka
    So, why does this code: package org.popoffka.apicross; import android.app.Activity; import android.os.Bundle; import android.widget.Button; public class Game extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Button testButton = new Button(this); testButton.setBackgroundResource(R.drawable.cell); testButton.setWidth(20); testButton.setHeight(20); setContentView(testButton); } } ...produce this thing: http://i42.tinypic.com/2hgdzme.png even though there's a setWidth(20) and setHeight(20) in the code? (R.drawable.cell is actually a 20x20 PNG image containing a white cell with a silver border)

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  • Class hierarchy problem (with generic's variance!)

    - by devoured elysium
    The problem: class StatesChain : IState, IHasStateList { private TasksChain tasks = new TasksChain(); ... public IList<IState> States { get { return _taskChain.Tasks; } } IList<ITask> IHasTasksCollection.Tasks { get { return _taskChain.Tasks; } <-- ERROR! You can't do this in C#! I want to return an IList<ITask> from an IList<IStates>. } } Assuming the IList returned will be read-only, I know that what I'm trying to achieve is safe (or is it not?). Is there any way I can accomplish what I'm trying? I wouldn't want to try to implement myself the TasksChain algorithm (again!), as it would be error prone and would lead to code duplication. Maybe I could just define an abstract Chain and then implement both TasksChain and StatesChain from there? Or maybe implementing a Chain<T> class? How would you approach this situation? The Details: I have defined an ITask interface: public interface ITask { bool Run(); ITask FailureTask { get; } } and a IState interface that inherits from ITask: public interface IState : ITask { IState FailureState { get; } } I have also defined an IHasTasksList interface: interface IHasTasksList { List<Tasks> Tasks { get; } } and an IHasStatesList: interface IHasTasksList { List<Tasks> States { get; } } Now, I have defined a TasksChain, that is a class that has some code logic that will manipulate a chain of tasks (beware that TasksChain is itself a kind of ITask!): class TasksChain : ITask, IHasTasksList { IList<ITask> tasks = new List<ITask>(); ... public List<ITask> Tasks { get { return _tasks; } } ... } I am implementing a State the following way: public class State : IState { private readonly TaskChain _taskChain = new TaskChain(); public State(Precondition precondition, Execution execution) { _taskChain.Tasks.Add(precondition); _taskChain.Tasks.Add(execution); } public bool Run() { return _taskChain.Run(); } public IState FailureState { get { return (IState)_taskChain.Tasks[0].FailureTask; } } ITask ITask.FailureTask { get { return FailureState; } } } which, as you can see, makes use of explicit interface implementations to "hide" FailureTask and instead show FailureState property. The problem comes from the fact that I also want to define a StatesChain, that inherits both from IState and IHasStateList (and that also imples ITask and IHasTaskList, implemented as explicit interfaces) and I want it to also hide IHasTaskList's Tasks and only show IHasStateList's States. (What is contained in "The problem" section should really be after this, but I thought puting it first would be way more reader friendly). (pff..long text) Thanks!

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  • Is MVVM killing silverlight development?

    - by DeanMc
    This is a question I have had rattling around in my head for some time. I had a chat with a guy the other night who told me he would not be using the navigational framework because he could not figure out how it works with MVVM. As much as I tried to explain that patterns should be taken with a pinch of salt he would not listen. My point is this, patterns are great when they solve some problem. Sometimes only part of the pattern solves a particular problem while the other parts of it cause different problems. The goal of any developer is to build a solid application using a combination of patterns know how and foresight. I feel MVVM is becoming the one pattern to rule them all. As it is not directly supported by .Net some fancy business is needed to make it work. I feel that people are missing the point of the pattern, which is loosely coupled, testable code and instead jumping through hoops and missing out on great experiences trying to follow MVVM to the letter. MVVM is great but I wish it came with a warning or disclaimer for newbies as my fear is people will shy away from silverlight development for fear of being smacked with the mvvm stick. EDIT: Can I just add as an edit, I use and agree with MVVM as a pattern I know when it is and isn't feasible in my projects. My issue is with the encompassing nature it is taking, as if it HAS to be used as part of development. It is being used as an integral feature and not a pattern, which it is.

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  • Domain model: should things like Logging, Audit, Persistence be in it

    - by hom.tanks
    I'm having a hard time convincing our architect that a Domain model should only have the essential elements of the business domain on it. Things like the fact that a class is persistable, that it needs logging and auditing and that it has a RESTful URI should not drive the domain model. They can be added later on, by using interfaces. Ours is a healthcare information management system. At the very coarse level, its a system where users login and access their healthcare information. They can share this information with others and be custodian for others' information (think Roles). But because of a few sound bytes that caught on early like "Everything should be a REST resource" the model now has a top level class called Resource that every other class extends from. I'm trying to make him see that the domain model should have well defined concepts like User Account, HealthDocument, UserRole etc which are distinct entities of the business , with specific associations between them. Clubbing everything under Resource class lets our model be inflexible besides being potentially incorrect. But he wants me to show him why its a bad idea to do it his way. I don't know how to articulate that properly but all my OO instincts tell me that its just not right. Any thoughts?

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  • c# - pull records from database without timeout

    - by BhejaFry
    Hi folks, i have a sql query with multiple joins & it pulls data from a database for processing. This is supposed to be running on some scheduled basis. So day 1, it might pull 500, day 2 say 400. Now, if the service is stopped for some reason & the data not processed, then on day3 there could be as much as 1000 records to process. This is causing timeout on the sql query. How best to handle this situation without causing timeout & gradually reducing workload to process? TIA

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  • How should i organize authority code?

    - by acidzombie24
    I have users that fall into the following Not logged in Not Verified Verified Moderator Admin All code that only admin and moderators can access (like banning) is in ModeratorUser which inherits from verified which inherits from BaseUser. Some pages are accessible to all users such as public profiles. If a user is logged in he can leave a comment. To check this i use if (IsVerifiedUser). Now here is the problem. To avoid problems if a user is banned he is not recognized as a verified user. However in the rare case i need to know if he is verified i can use usertype & Verified. Should i not be doing this? I have a bunch of code in my VerifiedUser class and find i am moving tons of it to BaseUser. Is this something i help because a not logged in user can access the page? Should i handle the ban user in a different way and allow IsVerifiedUser to be true even if the user is banned?

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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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  • [C++]Advantage of using a static member function instead of an equivalent non-static member function

    - by jonathanasdf
    I was wondering whether there's any advantages to using a static member function when there is a non-static equivalent. Will it result in faster execution (because of not having to care about all of the member variables), or maybe less use of memory (because of not being included in all instances)? Basically, the function I'm looking at is an utility function to rotate an integer array representing pixel colours an arbitrary number of degrees around an arbitrary centre point. It is placed in my abstract Bullet base class, since only the bullets will be using it and I didn't want the overhead of calling it in some utility class. It's a bit too long and used in every single derived bullet class, making it probably not a good idea to inline. How would you suggest I define this function? As a static member function of Bullet, of a non-static member function of Bullet, or maybe not as a member of Bullet but defined outside of the class in Bullet.h? What are the advantages and disadvantages of each?

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  • Sequence Diagram return a new constructed Object

    - by user256007
    I am drawing a Sequence Diagram where the scenario is. 1. an Actor calls :Table::query(query:String) :Table::query Calls :Connection::execute(query) :Connection::execute < a new :Row Object :Connection::execute calls :Row::fillData(result) :Connection::execute returns :Row ...... There are More But I am Stuck in Step 5 I cant Understand how to draw that, :Connection::execute returning the newly Constructed Row itself, in a Standard way.

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  • Designing a general database interface in PHP

    - by lamas
    I'm creating a small framework for my web projects in PHP so I don't have to do the basic work over and over again for every new website. It is not my goal to create a second CakePHP or Codeigniter and I'm also not planning to build my websites with any of the available frameworks as I prefer to use things I've created myself in general. I have no problems in designing that framework when it comes to parts like the core structure, request handling, and so on but I'm getting stuck with designing the database interface for my modules. I've already thought about using the MVC pattern but thought that it would be a bit of a overkill. So the exact problem I'm facing is how my frameworks modules (viewCustomers could be a module, for example) should interact with the database. Is it a good idea to write SQL directly in PHP (mysql_query( 'SELECT firstname, lastname(.....))? How could I abstract a query like SELECT firstname, lastname FROM customers WHERE id=X Would MySQL helper functions like $this->db->get( array('firstname', 'lastname'), array('id'=>X) ) be a good idea? I suppose not because they actually make everything more complicated by requiring arrays to be created and passed. Is the Model pattern from MVC my only real option?

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  • Creating combinations that have no more one intersecting element

    - by khuss
    I am looking to create a special type of combination in which no two sets have more than one intersecting element. Let me explain with an example: Let us say we have 9 letter set that contains A, B, C, D, E, F, G, H, and I If you create the standard non-repeating combinations of three letters you will have 9C3 sets. These will contain sets like ABC, ABD, BCD, etc. I am looking to create sets that have at the most only 1 common letter. So in this example, we will get following sets: ABC, ADG, AEI, AFH, BEH, BFG, BDI, CFI, CDH, CEG, DEF, and GHI - note that if you take any two sets there are no more than 1 repeating letter. What would be a good way to generate such sets? It should be scalable solution so that I can do it for a set of 1000 letters, with sub set size of 4. Any help is highly appreciated. Thanks

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  • Some questions regarding Flex

    - by Rachel
    For what real time scenarios/use cases one should go to Flex Technology ? What real time problems you have solved using Flex Technology ? What real time problems have you faced because of using Flex Technology and what was your work around for that use case ?

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  • Understanding MongoDB(and NoSQL in general) and How to make the best use of it

    - by Earlz
    Hello, I am beginning to think that my next project I am wanting to do would work better with a NoSQL solution. The project would either involve a ton of 2-column tables or a ton of dynamic queries with dynamically generated columns in a traditional SQL database. So I feel a NoSQL database would be much cleaner. I'm looking at MongoDB and it looks pretty promising. Anyway, I'm attempting to make sense of it all. Also, I will be using MongoMapper in Ruby. Anyway though, I'm confused as to how to layout things in such a freeform database. I've read http://stackoverflow.com/questions/2170152/nosql-best-practices and the answer there says that normalization is usually bad in a NoSQL DB. So how would be the best way of laying out say a simple blog with users, posts, and comments? My natural thought was to have 3 collections for each and then link them by a unique ID. But this apparently is wrong? So, what are some of the ways to lay out such a thing? My concern with the answer given in the other question is what if the author's name changed. You'd have to go through updating a ton of posts and comments. But is this an ok thing to do with NoSQL?

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  • Singleton Properties

    - by coffeeaddict
    Ok, if I create a singleton class and expose the singleton object through a public static property...I understand that. But my singleton class has other properties in it. Should those be static? Should those also be private? I just want to be able to access all properties of my singleton class by doing this: MySingletonClass.SingletonProperty.SomeProperty2 Where SingletonProperty returns me the single singleton instance. I guess my question is, how do you expose the other properties in the singleton class..make them private and then access them through your public singleton static property?

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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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  • Is it okay to use try catch inside finally?

    - by Hiral Lakdavala
    Hi, I am using a buffered writer and my code, closes the writer in the finally block. My code is like this. ........... BufferedWriter theBufferedWriter = null; try{ theBufferedWriter =..... .... ...... ..... } catch (IOException anException) { .... } finally { try { theBufferedWriter.close(); } catch (IOException anException) { anException.printStackTrace(); } } I have to use the try catch inside the clean up code in finally as theBufferedWriter might also throw an IOException. I do not want to throw this exception to the calling methos. Is it a good practice to use a try catch in finally? If not what is the alternative? Please suggest. Regards, Hiral

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  • Pros / Cons displaying list of users at login page

    - by Radu094
    We seem to have a lot of clients asking us to change the login screen in this manner: Display a list of all available users (thumbnail picture + name) User selects a username from the list A password prompt appears near the username User enters password then presses enter This sounds remarcably similar to the Windows XP login, which is probably where they got the ideea in the first place. There are only about 4 - 5 different users that can login at any given station, so implementing that list on one screen is feasable. So I was wondering if there are any usability experts with some word on this method of login. As far as I can tell, MS droped this behaviour in Vista/Win7, didn't they?

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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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  • Use of (non) qualified names

    - by AProgrammer
    If I want to use the name baz defined in package foo|bar|quz, I've several choices: provide fbq as a short name for foo|bar|quz and use fbq|baz use foo|bar|quz|baz import baz from foo|bar|quz|baz and then use baz (or an alias given in the import process) import all public symbols from foo|bar|quz|baz and then use baz For the languages I know, my perception is that the best practice is to use the first two ways (I'll use one or the other depending on the specific package full name and the number of symbols I need from it). I'd use the third only in a language which doesn't provide the first and hunt for supporting tools to write the import statements. And in my opinion the fourth should be reserved to package designed with than import in mind, for instance if all exported symbols start with a prefix or contains the name of the package. My questions: what is in your opinion the best practice for your favorite languages? what would you suggest in a new language? what would you suggest in an old language adding such a feature?

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