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  • Alternative to singleton for unique resources

    - by user1320881
    I keep reading over and over again that one should avoid using singletons for various reasons. I'm wondering how to correctly handle a situation where a class represents a unique system resource. For example, a AudioOutput class using SDL. Since SDL_OpenAudio can only be open once at a time it makes no sense having more then one object of this type and it seems to me preventing accidentally making more then one object would actually be good. Just wondering what experienced programmers think about this, am i missing another option ?

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  • Can't declare an abstract method private....

    - by Zombies
    I want to do this, yet I can't. Here is my scenario and rational. I have an abstract class for test cases that has an abstract method called test(). The test() method is to be defined by the subclass; it is to be implemented with logic for a certain application, such as CRMAppTestCase extends CompanyTestCase. I don't want the test() method to be invoked directly, I want the super class to call the test() method while the sub class can call a method which calls this (and does other work too, such as setting a current date-time right before the test is executed for example). Example code: public abstract class CompanyTestCase { //I wish this would compile, but it cannot be declared private private abstract void test(); public TestCaseResult performTest() { //do some work which must be done and should be invoked whenever //this method is called (it would be improper to expect the caller // to perform initialization) TestCaseResult result = new TestCaseResult(); result.setBeginTime(new Date()); long time = System.currentTimeMillis(); test(); //invoke test logic result.setDuration(System.currentTimeMillis() - time); return result; } } Then to extend this.... public class CRMAppTestCase extends CompanyTestCase { public void test() { //test logic here } } Then to call it.... TestCaseResult result = new CRMAppTestCase().performTest();

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  • When designing an event, is it a good idea to prevent listeners from being added twice?

    - by Matt
    I am creating an event-based API where a user can subscribe to an event by adding listener objects (as is common in Java or C#). When the event is raised, all subscribed listeners are invoked with the event information. I initially decided to prevent adding an event listener more than once. If a listener is added that already exists in the listener collection, it is not added again. However, after thinking about it some more, it doesn't seem that most event-based structures actually prevent this. Was my initial instinct wrong? I'm not sure which way to go here. I guess I thought that preventing addition of an existing listener would help to avoid a common programming error. Then again, it could also hide a bug that would lead to code being run multiple times when it shouldn't.

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  • Should i use TabContainer for multiple pages?

    - by Tim
    I'm considering if it is a good idea to use an ASP.Net TabContainer-Control in the way that every TabPanel contains content of a different page. For example: Next i want to implement in my application is the masterdata management. Normally i would create one aspx page for every masterdata-table (f.e. Customer - MD_Customer.aspx). Then i would add a link into my Menu to this page. Now i'm thinking of creating one aspx page for all(Masterdata.aspx) with a Tabcontainer and an UpdatePanel for every type of Masterdata. The link it the menu could have an additional MDType as URL-Parameter. My main concerns are related to performance(one "page" for every TabPanel currently means 7 "pages" in one) and maintainability because of increasing complexity. Is it a good approach or a bad idea? Thanks

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  • Do null SQLite Data fields take up extra memory?

    - by CSharperWithJava
    I'm using the built in sqlite library on the Android platform. I'm considering adding several general purpose fields that users will be able to use for their own custom applications, but these fields will be blank most of the time. My question is, how much overhead will these blank fields add to my database? Do null fields even take up per record memory in sqlite? If so, how much? I don't quite understand the inner workings of a sqlite database.

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  • Why is there "data" and "newtype" in Haskell?

    - by martingw
    To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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  • db optimization - have a total field or query table?

    - by Dorian Fife
    I have an app where users get points for actions they perform - either 1 point for an easy action or 2 for a difficult one. I wish to display to the user the total number of points he got in my app and the points obtained this week (since Monday at midnight). I have a table that records all actions, along with their time and number of points. I have two alternatives and I'm not sure which is better: Every time the user sees the report perform a query and sum the points the user got Add two fields to each user that records the number of points obtained so far (total and weekly). The weekly points value will be set to 0 every Monday at midnight. The first option is easier, but I'm afraid that as I'll get many users and actions queries will take a long time. The second option bares the risk of inconsistency between the table of actions and the summary values. I'm very interested in what you think is the best alternative here. Thanks, Dorian

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  • How can I get a property as an Entity in Action of Asp.Net Mvc ?

    - by Felipe
    Hi all, i'd like to know how can I get a property like an entity, for example: My Model: public class Product { public int Id { get; set; } public string Name { get; set; } public Category Category { get; set; } } View: Name: <%=Html.TextBoxFor(x => x.Name) %> Category: <%= Html.DropDownList("Category", IEnumerable<SelectListItem>)ViewData["Categories"]) %> Controller: public ActionResult Save(Product product) { /// produtct.Category ??? } and how is the category property ? It's fill by the view ? ASP.Net MVC know how to fill this object by ID ? Thanks!

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  • Several C# Language Questions

    - by Water Cooler v2
    1) What is int? Is it any different from the struct System.Int32? I understand that the former is a C# alias (typedef or #define equivalant) for the CLR type System.Int32. Is this understanding correct? 2) When we say: IComparable x = 10; Is that like saying: IComparable x = new System.Int32(); But we can't new a struct, right? or in C like syntax: struct System.In32 *x; x=>someThing = 10; 3) What is String with a capitalized S? I see in Reflector that it is the sealed String class, which, of course, is a reference type, unlike the System.Int32 above, which is a value type. What is string, with an uncapitalized s, though? Is that also the C# alias for this class? Why can I not see the alias definitions in Reflector? 4) Try to follow me down this subtle train of thought, if you please. We know that a storage location of a particular type can only access properties and members on its interface. That means: Person p = new Customer(); p.Name = "Water Cooler v2"; // legal because as Name is defined on Person. but // illegal without an explicit cast even though the backing // store is a Customer, the storage location is of type // Person, which doesn't support the member/method being // accessed/called. p.GetTotalValueOfOrdersMade(); Now, with that inference, consider this scenario: int i = 10; // obvious System.object defines no member to // store an integer value or any other value in. // So, my question really is, when the integer is // boxed, what is the *type* it is actually boxed to. // In other words, what is the type that forms the // backing store on the heap, for this operation? object x = i; Update Thank you for your answers, Eric Gunnerson and Aaronought. I'm afraid I haven't been able to articulate my questions well enough to attract very satisfying answers. The trouble is, I do know the answers to my questions on the surface, and I am, by no means, a newbie programmer. But I have to admit, a deeper understanding to the intricacies of how a language and its underlying platform/runtime handle storage of types has eluded me for as long as I've been a programmer, even though I write correct code.

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  • How do I manipulate a tree of immutable objects?

    - by Frederik
    I'm building an entire application out of immutable objects so that multi-threading and undo become easier to implement. I'm using the Google Collections Library which provides immutable versions of Map, List, and Set. My application model looks like a tree: Scene is a top-level object that contains a reference to a root Node. Each Node can contain child Nodes and Ports. An object graph might look like this: Scene | +-- Node | +-- Node | +- Port +-- Node | +- Port +- Port If all of these objects are immutable, controlled by a top-level SceneController object: What is the best way to construct this hierarchy? How would I replace an object that is arbitrarily deep in the object tree? Is there a way to support back-links, e.g. a Node having a "parent" attribute?

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  • Is throwing an exception a healthy way to exit?

    - by ramaseshan
    I have a setup that looks like this. class Checker { // member data Results m_results; // see below public: bool Check(); private: bool Check1(); bool Check2(); // .. so on }; Checker is a class that performs lengthy check computations for engineering analysis. Each type of check has a resultant double that the checker stores. (see below) bool Checker::Check() { // initilisations etc. Check1(); Check2(); // ... so on } A typical Check function would look like this: bool Checker::Check1() { double result; // lots of code m_results.SetCheck1Result(result); } And the results class looks something like this: class Results { double m_check1Result; double m_check2Result; // ... public: void SetCheck1Result(double d); double GetOverallResult() { return max(m_check1Result, m_check2Result, ...); } }; Note: all code is oversimplified. The Checker and Result classes were initially written to perform all checks and return an overall double result. There is now a new requirement where I only need to know if any of the results exceeds 1. If it does, subsequent checks need not be carried out(it's an optimisation). To achieve this, I could either: Modify every CheckN function to keep check for result and return. The parent Check function would keep checking m_results. OR In the Results::SetCheckNResults(), throw an exception if the value exceeds 1 and catch it at the end of Checker::Check(). The first is tedious, error prone and sub-optimal because every CheckN function further branches out into sub-checks etc. The second is non-intrusive and quick. One disadvantage is I can think of is that the Checker code may not necessarily be exception-safe(although there is no other exception being thrown anywhere else). Is there anything else that's obvious that I'm overlooking? What about the cost of throwing exceptions and stack unwinding? Is there a better 3rd option?

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  • How to write this in better way?

    - by dario
    Hi all. Let's look at this code: IList<IHouseAnnouncement> list = new List<IHouseAnnouncement>(); var table = adapter.GetData(); //get data from repository object -> DataTable if (table.Rows.Count >= 1) { for (int i = 0; i < table.Rows.Count-1; i++) { var anno = new HouseAnnouncement(); anno.Area = float.Parse(table.Rows[i][table.powierzchniaColumn].ToString()); anno.City = table.Rows[i][table.miastoColumn].ToString(); list.Add(anno); } } return list; Is it better way to write this in less code and better fashion (must be :-) )? Maybe using labda (but let mi know how)? Thanks in advance!

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  • Magic Method __set() on a Instanciated Object

    - by streetparade
    Ok i have a problem, sorry if i cant explaint it clear but the code speaks for its self. i have a class which generates objects from a given class name; Say we say the class is Modules: public function name($name) { $this->includeModule($name); try { $module = new ReflectionClass($name); $instance = $module->isInstantiable() ? $module->newInstance() : "Err"; $this->addDelegate($instance); } catch(Exception $e) { Modules::Name("Logger")->log($e->getMessage()); } return $this; } The AddDelegate Method: protected function addDelegate($delegate) { $this->aDelegates[] = $delegate; } The __call Method public function __call($methodName, $parameters) { $delegated = false; foreach ($this->aDelegates as $delegate) { if(class_exists(get_class($delegate))) { if(method_exists($delegate,$methodName)) { $method = new ReflectionMethod(get_class($delegate), $methodName); $function = array($delegate, $methodName); return call_user_func_array($function, $parameters); } } } The __get Method public function __get($property) { foreach($this->aDelegates as $delegate) { if ($delegate->$property !== false) { return $delegate->$property; } } } All this works fine expect the function __set public function __set($property,$value) { //print_r($this->aDelegates); foreach($this->aDelegates as $k=>$delegate) { //print_r($k); //print_r($delegate); if (property_exists($delegate, $property)) { $delegate->$property = $value; } } //$this->addDelegate($delegate); print_r($this->aDelegates); } class tester { public function __set($name,$value) { self::$module->name(self::$name)->__set($name,$value); } } Module::test("logger")->log("test"); // this logs, it works echo Module::test("logger")->path; //prints /home/bla/test/ this is also correct But i cant set any value to class log like this Module::tester("logger")->path ="/home/bla/test/log/"; The path property of class logger is public so its not a problem of protected or private property access. How can i solve this issue? I hope i could explain my problem clear.

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  • Which database should I use for best performance

    - by _simon_
    Hello, I am working in Visual Studio 2005, .NET 2.0. I need to write an application, which listens on COM port and saves incoming data to a database. Main feature: save incoming data (series of 13-digits numbers), if this number allready exists, then mark it as double. For example, there could be these records in database: 0000000000001 OK 0000000000002 OK 0000000000002 Double 0000000000003 OK 0000000000004 OK I could use SQL database, but I don't know if it is fast enough... Database should be able to store up to 10.000.000 records and write up to 100 records per minute (so it needs to check 100 times per minute if this record allready exists). Which database should I use? Maybe the whole database would need to be in RAM. Where could I learn more about this? Thanks

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  • How to make 2 incompatible types, but with the same members, interchangeable?

    - by Quigrim
    Yesterday 2 of the guys on our team came to me with an uncommon problem. We are using a third-party component in one of our winforms applications. All the code has already been written against it. They then wanted to incorporate another third-party component, by the same vender, into our application. To their delight they found that the second component had the exact same public members as the first. But to their dismay, the 2 components have completely separate inheritance hierarchies, and implement no common interfaces. Makes you wonder... Well, makes me wonder. An example of the problem: public class ThirdPartyClass1 { public string Name { get { return "ThirdPartyClass1"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass1 is doing its thing."); } } public class ThirdPartyClass2 { public string Name { get { return "ThirdPartyClass2"; } } public void DoThirdPartyStuff () { Console.WriteLine ("ThirdPartyClass2 is doing its thing."); } } Gladly they felt copying and pasting the code they wrote for the first component was not the correct answer. So they were thinking of assigning the component instant into an object reference and then modifying the code to do conditional casts after checking what type it was. But that is arguably even uglier than the copy and paste approach. So they then asked me if I can write some reflection code to access the properties and call the methods off the two different object types since we know what they are, and they are exactly the same. But my first thought was that there goes the elegance. I figure there has to be a better, graceful solution to this problem.

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  • Is passing a struct value to a method by-reference in C# an acceptable optimization?

    - by Arc
    Say I have a struct: struct MyStruct { public int X public int Y } And a method in some class that is iterated over many times elsewhere: public bool MyMethod( MyStruct myStruct ) { return ... } Is changing the MyMethod signature to the following an acceptable optimization? public bool MyMethod( ref MyStruct myStruct ) If so, how much of an advantage would it really be? If not, about how many fields would a struct need for a big enough advantage using ref this way?

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  • Solving problems with near infinite potential solutions

    - by Zonda333
    Today I read the following problem: Use the digits 2, 0, 1, 1 and the operations +, -, x, ÷, sqrt, ^ , !, (), combinations, and permutations to write equations for the counting numbers 1 through 100. All four digits must be used in each expression. Only the digits 2, 0, 1, 1 may be used, and each must be used exactly once. Decimals may be used, as in .1, .02, etc. Digits may be combined; numbers such as 20 or 101 may be used. Example: 60 = 10*(2+1)!, 54 = ¹¹C2 - 0! Though I was able to quickly find around 50 solutions quite easily in my head, I thought programming it would be a far superior solution. However, I then realized I had no clue how to go about solving a problem like this. I am not asking for complete code for me to copy and paste, but for ideas about how I would solve this problems, and others like it that have nearly infinite potential solutions. As I will be writing it in python, where I have the most experience, I would prefer if the answers were more python based, but general ideas are great too.

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  • DDD: Where to create entity objects?

    - by ciscoheat
    I have three entities that must interact: User, SupportTicketand PhoneConversation. When someone calls in requesting help, the User should have a SupportTicket assigned to him, with a PhoneConversation assigned to the Ticked describing the call. My question is: In what entity should I put the method CreatePhoneSupportTicket() that creates a new SupportTicket and a PhoneConversation, relates them to each other and finally relates the SupportTicket to the User? I'm guessing it can't be on the user because that would violate the SRP (the user does a few more things). But the method itself does more than one thing, it should create both a SupportTicket and a PhoneConversation. Is this a situation when a Service is a better solution then putting methods on entities? Thanks for your help!

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  • The best way to structure this database?

    - by James P
    At the moment I'm doing this: gems(id, name, colour, level, effects, source) id is the primary key and is not auto-increment. A typical row of data would look like this: id => 40153 name => Veiled Ametrine colour => Orange level => 80 effects => +12 sp, +10 hit source => Ametrine (Some of you gamers might see what I'm doing here :) ) But I realise this could be sorted a lot better. I have studied database relationships and secondary keys in my A-Level computing class but never got as far as to set one up properly. I just need help with how this database should be organised, like what tables should have what data with what secondary and foreign keys? I was thinking maybe 3 tables: gem, effects, source. Which then have relationships to each other? Can anyone shed some light on this? Is a complex way like I'm proposing really the way to go or should I just carry on with what I'm doing? Cheers.

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  • What's the best way to handle modules that use each other?

    - by Axeman
    What's the best way to handle modules that use each other? Let's say I have a module which has functions for hashes: # Really::Useful::Functions::On::Hash.pm use base qw<Exporter>; use strict; use warnings; use Really::Useful::Functions::On::List qw<transform_list>; our @EXPORT_OK = qw<transform_hash transform_hash_as_list ...>; #... sub transform_hash { ... } #... sub transform_hash_as_list { return transform_list( %{ shift() } ); } #... 1 And another module has been segmented out for lists: # Really::Useful::Functions::On::List.pm use base qw<Exporter>; use strict; use warnings; use Really::Useful::Functions::On::Hash qw<transform_hash>; our @EXPORT_OK = qw<transform_list some_func ...>; #... sub transform_list { ... } #... sub some_func { my %params = transform_hash @_; #... } #... 1 Suppose that enough of these utility functions are handy enough that I'll want to use them in BEGIN statements and import functions to process parameter lists or configuration data. I have been putting sub definitions into BEGIN blocks to make sure they are ready to use whenever somebody includes the module. But I have gotten into hairy race conditions where a definition is not completed in a BEGIN block. I put evolving code idioms into modules so that I can reuse any idiom I find myself coding over and over again. For instance: sub list_if { my $condition = shift; return unless $condition; my $more_args = scalar @_; my $arg_list = @_ > 1 ? \@_ : @_ ? shift : $condition; if (( reftype( $arg_list ) || '' ) eq 'ARRAY' ) { return wantarray ? @$arg_list : $arg_list; } elsif ( $more_args ) { return $arg_list; } return; } captures two idioms that I'm kind of tired of typing: @{ func_I_hope_returns_a_listref() || [] } and ( $condition ? LIST : ()) The more I define functions in BEGIN blocks, the more likely I'll use these idiom bricks to express the logic the more likely that bricks are needed in BEGIN blocks. Do people have standard ways of dealing with this sort of language-idiom-brick model? I've been doing mostly Pure-Perl; will XS alleviate some of this?

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  • How to handle ids and polymorphic associations in views if compound keys are not supported?

    - by duncan
    I have a Movie plan table: movie_plans (id, description) Each plan has items, which describe a sequence of movies and the duration in minutes: movie_plan_items (id, movie_plan_id, movie_id, start_minutes, end_minutes) A specific instance of that plan happens in: movie_schedules (id, movie_plan_id, start_at) However the schedule items can be calculated from the movie_plan_items and the schedule start time by adding the minutes create view movie_schedule_items as select CONCAT(p.id, '-', s.id) as id, s.id as movie_schedule_id, p.id as movie_plan_item_id, p.movie_id, p.movie_plan_id, (s.start_at + INTERVAL p.start_minutes MINUTE) as start_at, (s.start_at + INTERVAL p.end_minutes MINUTE) as end_at from movie_plan_items p, movie_schedules s where s.movie_plan_id=p.movie_plan_id; I have a model over this view (readonly), it works ok, except that the id is right now a string. I now want to add a polymorphic property (like comments) to various of the previous tables. Therefore for movie_schedule_items I need a unique and persistent numeric id. I have the following dilemma: I could avoid the id and have movie_schedule_items just use the movie_plan_id and movie_schedule_id as a compound key, as it should. But Rails sucks in this regard. I could create an id using String#hash or a md5, thus making it slower or collision prone (and IIRC String#hash is no longer persistent across processes in Ruby 1.9) Any ideas on how to handle this situation?

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