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  • What's the point of the Prototype design pattern?

    - by user1905391
    So I'm learning about design patterns in school. Many of them are silly little ideas, but nevertheless solve some recurring problems(singleton, adapters, asynchronous polling, ect). But today I was told about the so called 'Prototype' design pattern. I must be missing something, because I don't see any benefits from it. I've seen people online say it's faster than using "new"' but this is doesn't make any sense, since at some point, regardless how the new object is created, memory needs to be allocated for it ect. Furthermore, doesn't this pattern run in the same circles as the 'chicken or egg' problem? By this I mean, since the prototype pattern essentially is just cloning objects, at some point the original object must be created itself (ie, not cloned). So this would mean, that I would need to have an existing copy of every object that I would ever want to clone already ready to clone? Seems stupid to me. Can anyone explain what the use of this pattern is? Original post: http://stackoverflow.com/questions/13887704/whats-the-point-of-the-prototype-design-pattern

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  • xslt broken: pattern does not match

    - by krisvandenbergh
    I'm trying to query an xml file using the following xslt: <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:bpmn="http://dkm.fbk.eu/index.php/BPMN_Ontology"> <!-- Participants --> <xsl:template match="/"> <html> <body> <table> <xsl:for-each select="Package/Participants/Participant"> <tr> <td><xsl:value-of select="ParticipantType" /></td> <td><xsl:value-of select="Description" /></td> </tr> </xsl:for-each> </table> </body> </html> </xsl:template> </xsl:stylesheet> Here's the contents of the xml file: <?xml version="1.0" encoding="utf-8"?> <?xml-stylesheet type="text/xsl" href="xpdl2bpmn.xsl"?> <Package xmlns="http://www.wfmc.org/2008/XPDL2.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" Id="25ffcb89-a9bf-40bc-8f50-e5afe58abda0" Name="1 price setting" OnlyOneProcess="false"> <PackageHeader> <XPDLVersion>2.1</XPDLVersion> <Vendor>BizAgi Process Modeler.</Vendor> <Created>2010-04-24T10:49:45.3442528+02:00</Created> <Description>1 price setting</Description> <Documentation /> </PackageHeader> <RedefinableHeader> <Author /> <Version /> <Countrykey>CO</Countrykey> </RedefinableHeader> <ExternalPackages /> <Participants> <Participant Id="008af9a6-fdc0-45e6-af3f-984c3e220e03" Name="customer"> <ParticipantType Type="RESOURCE" /> <Description /> </Participant> <Participant Id="1d2fd8b4-eb88-479b-9c1d-7fe6c45b910e" Name="clerk"> <ParticipantType Type="ROLE" /> <Description /> </Participant> </Participants> </Package> Despite, the simple pattern, the foreach doesn't work. What is wrong with Package/Participants/Participant ? What do I miss here? Thanks a lot!

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  • Matching unmatched strings based on a unknown pattern

    - by Polity
    Alright guys, i really hurt my brain over this one and i'm curious if you guys can give me any pointers towards the right direction i should be taking. The situation is this: Lets say, i have a collection of strings (let it be clear that the pattern of this strings is unknown. For a fact, i can say that the string contain only signs from the ASCII table and therefore, i dont have to worry about weird Chinese signs). For this example, i take the following collection of strings (note that the strings dont have to make any human sence so dont try figguring them out :)): "[001].[FOO].[TEST] - 'foofoo.test'", "[002].[FOO].[TEST] - 'foofoo.test'", "[003].[FOO].[TEST] - 'foofoo.test'", "[001].[FOO].[TEST] - 'foofoo.test.sample'", "[002].[FOO].[TEST] - 'foofoo.test.sample'", "-001- BAR.[TEST] - 'bartest.xx1", "-002- BAR.[TEST] - 'bartest.xx1" Now, what i need to have is a way of finding logical groups (and subgroups) of these set of strings, so in the above example, just by rational thinking, you can combine the first 3, the 2 after that and the last 2. Also the resulting groups from the first 5 can be combined in one main group with 2 subgroups, this should give you something like this: { { "[001].[FOO].[TEST] - 'foofoo.test'", "[002].[FOO].[TEST] - 'foofoo.test'", "[003].[FOO].[TEST] - 'foofoo.test'", } { "[001].[FOO].[TEST] - 'foofoo.test.sample'", "[002].[FOO].[TEST] - 'foofoo.test.sample'", } { "-001- BAR.[TEST] - 'bartest.xx1", "-002- BAR.[TEST] - 'bartest.xx1" } } Sorry for the layout above but indenting with 4 spaces doesnt seem to work correctly (or im frakk'n it up). Anyways, I'm not sure how to approach this problem (how to get the result desired as indicated above). First of, i thought of creating a huge set of regexes which would parse most known patterns but the amount of different patterns is just to huge that this isn't realistic. Another think i thought of was parsing each indidual word within a string (so strip all non alphabetic or numeric characters and split by those), and if X% matches, i can assume the strings belong to the same group. (where X wil probably be around 80/90). However, i find the area of speculation kinda big. For example, when matching strings with each 20 words, the change of hitting above 80% is kinda big (that means that 4 words can differ), however when matching only 8 words, 2 words at most can differ. My question to you is, what would be a logical approach in the above situation? Thanks in advance!

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  • help with php/cake error

    - by adam
    I tried to clone beta.neighborrow.com - i copied the directory file for file but im getting this error on the new url instillbliss.neighborrow.com Warning: require(cake/basics.php) [function.require]: failed to open stream: No such file or directory in /home/neighborrow/instillbliss.neighborrow.com/index.php on line 53 Fatal error: require() [function.require]: Failed opening required 'cake/basics.php' (include_path='.:/usr/local/lib/php:/usr/local/php5/lib/pear:/home/neighborrow/instillbliss.neighborrow.com:/home/neighborrow/instillbliss.neighborrow.com/app/') in /home/neighborrow/instillbliss.neighborrow.com/index.php on line 53

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  • c#Repository pattern: One repository per subclass?

    - by Alex
    I am wondering if you would create a repository for each subclass of a domain model. There are two classes for example: public class Person { public virtual String GivenName { set; get; } public virtual String FamilyName { set; get; } public virtual String EMailAdress { set; get; } } public class Customer : Person { public virtual DateTime RegistrationDate { get; set; } public virtual String Password { get; set; } } Would you create both a PersonRepository and a CustomerRepository or just the PersonRepository which would also be able to execute Customer related queries?

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  • pattern matching in Bash

    - by Tim
    Hi, Here is an example to get different parts of a filename bash-3.2$ pathandfile=/tmp/ff.txt bash-3.2$ filename=$(basename $pathandfile) bash-3.2$ echo $filename ff.txt bash-3.2$ echo ${filename##*.} txt bash-3.2$ echo ${filename%.*} ff I was wondering what does ## and % mean in the patterns. How is the patten matching working? Thanks and regards!

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  • Looking for ideas for a simple pattern matching algorithm to run on a microcontroller

    - by pic_audio
    I'm working on a project to recognize simple audio patterns. I have two data sets, each made up of between 4 and 32 note/duration pairs. One set is predefined, the other is from an incoming data stream. The length of the two strongly correlated data sets is often different, but roughly the same "shape". My goal is to come up with some sort of ranking as to how well the two data sets correlate/match. I have converted the incoming frequencies to pitch and shifted the incoming data stream's pitch so that it's average pitch matches that of the predefined data set. I also stretch/compress the incoming data set's durations to match the overall duration of the predefined set. Here are two graphical examples of data that should be ranked as strongly correlated: http://s2.postimage.org/FVeG0-ee3c23ecc094a55b15e538c3a0d83dd5.gif (Sorry, as a new user I couldn't directly post images) I'm doing this on a 8-bit microcontroller so resources are minimal. Speed is less an issue, a second or two of processing isn't a deal breaker. It wouldn't surprise me if there is an obvious solution, I've just been staring at the problem too long. Any ideas? Thanks in advance...

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  • ocaml pattern match question

    - by REALFREE
    I'm trying to write a simple recursive function that look over list and return a pair of integer. This is easy to write in c/c++/java but i'm new to ocaml so somehow hard to find out the solution due to type conflict it goes like.. let rec test l = match l with [] - 0 | x::xs - if x 0 then (1+test, 0) else (0, 1+test);; I kno this is not correct one and kinda awkward.. but any help will be appreciated

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  • Pattern matching in Perl ala Haskell

    - by Paul Nathan
    In Haskell (F#, Ocaml, and others), I can do this: sign x | x > 0 = 1 | x == 0 = 0 | x < 0 = -1 Which calculates the sign of a given integer. This can concisely express certain logic flows; I've encountered one of these flows in Perl. Right now what I am doing is sub frobnicator { my $frob = shift; return "foo" if $frob eq "Foomaticator"; return "bar" if $frob eq "Barmaticator"; croak("Unable to frob legit value: $frob received"); } Which feels inexpressive and ugly. This code has to run on Perl 5.8.8, but of course I am interested in more modern techniques as well.

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  • F# pattern matching

    - by Roger Alsing
    What would be the most effective way to express the following code? match cond.EvalBool() with | true -> match body.Eval() with | :? ControlFlowModifier as e -> match e with | Break(scope) -> e :> obj //Break is a DU element of ControlFlowModifier | _ -> next() //other members of CFM should call next() | _ -> next() | false -> null cond.EvalBool returns a boolean result where false should return null and true should either run the entire block again (its wrapped in a func called next) or if the special value of break is found, then the loop should exit and return the break value. Is there any way to compress that block of code to something smaller?

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  • Strategy Design Pattern -- *dynamic* !!!

    - by alexeypro
    My application will have different strategies for my objects. What's the best way of implementing that? I would really love the case when we can make strategy classes implementation dynamically loaded from, say, some relational database. Not sure how do that better, though. What's the best approach? Idea is that say we want to apply to object MyObj strategy Strategy123 then we just load from database by ID 123 the object, deserialize it, get the Strategy class, and use it with MyObj. The maintenance while sounds easier from the first look can be a pain in the long run if Strategy interfaces changes, etc. What can I do also? I want to find solution when I should be keeping Strategy classes in codebase -- just for the sake that I don't need code change and re-deployment of the application if my Strategy changes, or I add new strategy. Please advise!

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  • Question regarding factory pattern

    - by eriks
    I have a factory class to build objects of base class B. The object (D) that uses this factory received a list of strings representing the actual types. What is the correct implementation: the factory receives an Enum (and uses switch inside the Create function) and D is responsible to convert the string to Enum. the factory receives a string and checks for a match to a set of valid strings (using ifs') other implementation i didn't think of.

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  • Need a design pattern for representing multiple information sources

    - by hsmit
    I'm building a Java application that retrieves information from differing information sources. I'm using a sensor, a set of RecordStores and a few online web services. In the basic application all these resources are loaded by default. Some of these sources are directly read in a separate thread (load database, read sensor etc.). From this basic application some functions are started that use these sources. The classes that contain these functions (usually combining multiple sources information) are currently paramterized with a set of resources like this: AppPart a1 = new AppPart(source1, source2, source3); I could also do it like this AppPart a1 = new AppPart(this); ..where I need to make my sources public in order to read them. I'm also thinking about a kind of stage/collection to publish all sources on, e.g: public SourceCollectionStage sStage = new SourceCollectionStage(); and later: sStage.getSensor(); .. for example. What do you guys think is the best or most often used way to do this? Btw: the user interface is often implemented by the specific funtion classes, not by the main class. Should I do this in another way?

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  • "Pattern matching" of algebraic type data constructors

    - by jetxee
    Let's consider a data type with many constructors: data T = Alpha Int | Beta Int | Gamma Int Int | Delta Int I want to write a function to check if two values are produced with the same constructor: sameK (Alpha _) (Alpha _) = True sameK (Beta _) (Beta _) = True sameK (Gamma _ _) (Gamma _ _) = True sameK _ _ = False Maintaining sameK is not much fun, it is potentially buggy. For example, when new constructors are added to T, it's easy to forget to update sameK. I omitted one line to give an example: -- it’s easy to forget: -- sameK (Delta _) (Delta _) = True The question is how to avoid boilerplate in sameK? Or how to make sure it checks for all T constructors? The workaround I found is to use separate data types for each of the constructors, deriving Data.Typeable, and declaring a common type class, but I don't like this solution, because it is much less readable and otherwise just a simple algebraic type works for me: {-# LANGUAGE DeriveDataTypeable #-} import Data.Typeable class Tlike t where value :: t -> t value = id data Alpha = Alpha Int deriving Typeable data Beta = Beta Int deriving Typeable data Gamma = Gamma Int Int deriving Typeable data Delta = Delta Int deriving Typeable instance Tlike Alpha instance Tlike Beta instance Tlike Gamma instance Tlike Delta sameK :: (Tlike t, Typeable t, Tlike t', Typeable t') => t -> t' -> Bool sameK a b = typeOf a == typeOf b

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  • Is a "factory" method the right pattern?

    - by jdt141
    Hey all - So I'm working to improve an existing implementation. I have a number of polymorphic classes that are all composed into a higher level container class. The problem I'm dealing with at the moment is that the higher level container class, well, sucks. It looks something like this, which I really don't have a problem with (as the polymorphic classes in the container should be public). My real issue is the constructor... /* * class1 and class 2 derive from the same superclass */ class Container { public: boost::shared_ptr<ComposedClass1> class1; boost::shared_ptr<ComposedClass2> class2; private: ... } /* * Constructor - builds the objects that we need in this container. */ Container::Container(some params) { class1.reset(new ComposedClass1(...)); class2.reset(new ComposedClass2(...)); } What I really need is to make this container class more re-usable. By hard-coding up the member objects and instantiating them, it basically isn't and can only be used once. A factory is one way to build what I need (potentially by supplying a list of objects and their specific types to be created?) Other ways to get around this problem? Seems like someone should have solved it before... Thanks!

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  • What design pattern will you choose ?

    - by MemoryLeak
    I want to design a class, which contains a procedure to achieve a goal. And it must follow some order to make sure the last method, let's say "ExecuteIt", to behave correctly. in such a case, what design patter will you use ? which can make sure that the user must call the public method according some ordering. If you really don't know what I am saying, then can you share me some concept of choosing a design patter, or what will you consider while design a class?

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  • Factory Method pattern and public constructor

    - by H4mm3rHead
    Hi, Im making a factory method that returns new instances of my objects. I would like to prevent anyone using my code from using a public constructor on my objects. Is there any way of doing this? How is this typically accomplished: public abstract class CarFactory { public abstract ICar CreateSUV(); } public class MercedesFactory : CarFactory { public override ICar CreateSUV() { return new Mercedes4WD(); } } I then would like to limit/prevent the other developers (including me in a few months) from making an instance of Mercedes4WD. But make them call my factory method. How to?

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  • Software Architecture: Unit of Work design pattern discussion

    - by santiagobasulto
    Hey everybody. According Martin Fowler's Unit of Work description: "Maintains a list of objects that are affected by a business transaction and coordinates the writing out of changes and resolution of concurrency problems." Avoiding very small calls to the database, which ends up being very slow I'm wondering. If we just delimit it to database transaction management, won't prepare statements help with this?

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  • NSString simple pattern matching

    - by SirRatty
    Hi all, Mac OS 10.6, Cocoa project, 10.4 compatibility required. (Please note: my knowledge of regex is quite slight) I need to parse NSStrings, for matching cases where the string contains an embedded tag, where the tag format is: [xxxx] Where xxxx are random characters. e.g. "The quick brown [foxy] fox likes sox". In the above case, I need to grab the string "foxy". (Or nil if no tag is found.) Each string will only have one tag, and the tag can appear anywhere within the string, or may not appear at all. Could someone please help with a way to do that, preferably without having to include another library such as RegexKit. Thank you for any help.

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