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  • Do any languages other than haskell/agda have a hindley-milner type system and type classes?

    - by Jimmy Hoffa
    In pondering what gives Haskell such a layer of mental pain in becoming proficient the main thing I can think of are the Monads, Applicatives, Functors, and gaining an intuition to know how a list or maybe will behave in regards to sequence or alternate or bind etc. But why haven't other languages presented these same concepts given the usefulness of monads/applicatives/etc? It occurs to me, type classes are the key, so the question is: Have any languages other than Haskell/Agda actually implemented type classes in the same or similar way?

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  • Nested Classes: A useful tool or an encapsulation violation?

    - by Bryan Harrington
    So I'm still on the fence as to whether or not I should be using these or not. I feel its an extreme violation of encapsulation, however I find that I am able to achieve some degree of encapsulation while gaining more flexibility in my code. Previous Java/Swing projects I had used nested classes to some degree, However now I have moved into other projects in C# and I am avoid their use. How do you feel about nested classes?

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  • Testing C++ program with Testing classes over normally used classes

    - by paultop6
    Hi Guys, This will probably be a bot of a waffly question but ill try my best. I have a simple c++ program that i need to build testing for. I have 2 Classes i use besides the one i actually am using, these are called WebServer and BusinessLogicLayer. To test my own code i have made my own versions of these classes that feed dummy data to my class to test it functionality. I need to know a way of somehow, via a makefile for instance, how to tell the source code to use the test classes over the normally used classes. The test classes are in a different "tester" c++ file, and the tester c++ file also has its own header file. Regards Paul P.S. This is probably a badly worded question, but i dont know any better way to put my question.

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  • Extending mysqli and using multiple classes

    - by Mikk
    Hi, I'm new to PHP oop stuff. I'm trying to create class database and call other classes from it. Am I doing it the right way? class database: class database extends mysqli { private $classes = array(); public function __construct() { parent::__construct('localhost', 'root', 'password', 'database'); if (mysqli_connect_error()) { $this->error(mysqli_connect_errno(), mysqli_connect_error()); } } public function __call($class, $args) { if (!isset($this->classes[$class])) { $class = 'db_'.$class; $this->classes[$class] = new $class(); } return $this->classes[$class]; } private function error($eNo, $eMsg) { die ('MySQL error: ('.$eNo.': '.$eMsg); } } class db_users: class db_users extends database { public function test() { echo 'foo'; } } and how I'm using it $db = new database(); $db->users()->test(); Is it the right way or should it be done another way? Thank you.

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  • SQL Full Outer Join

    - by Torment March
    I have a table named 'Logs' with the following values : CheckDate CheckType CheckTime ------------------------------------------- 2011-11-25 IN 14:40:00 2011-11-25 OUT 14:45:00 2011-11-25 IN 14:50:00 2011-11-25 OUT 14:55:00 2011-11-25 IN 15:00:00 2011-11-25 OUT 15:05:00 2011-11-25 IN 15:15:00 2011-11-25 OUT 15:20:00 2011-11-25 IN 15:25:00 2011-11-25 OUT 15:30:00 2011-11-25 OUT 15:40:00 2011-11-25 IN 15:45:00 I want to use the previous table to produce a result of: CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 14:40:00 14:45:00 2011-11-25 14:50:00 14:55:00 2011-11-25 15:00:00 15:05:00 2011-11-25 15:15:00 15:20:00 2011-11-25 15:25:00 15:30:00 2011-11-25 NULL 15:40:00 2011-11-25 15:45:00 NULL So far I have come up with this result set : CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 14:40:00 14:45:00 2011-11-25 14:50:00 14:55:00 2011-11-25 15:00:00 15:05:00 2011-11-25 15:15:00 15:20:00 2011-11-25 15:25:00 15:30:00 2011-11-25 15:45:00 NULL The problem is I cannot generate the log without CheckIns : CheckDate CheckIn CheckOut ----------------------------------------- 2011-11-25 NULL 15:40:00 The sequence of CheckIn - CheckOut pairing and order is in increasing time value.

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  • Type classes or implicit parameters? What do you prefer and why? [closed]

    - by Petr Pudlák
    I was playing a bit with Scalaz and I realized that Haskell's type classes are very similar to Scala's implicit parameters. While Haskell passes the methods defined by a type class using hidden dictionaries, Scala allows a similar thing using implicit parameters. For example, in Haskell, one could write: incInside :: (Functor f) => f Int -> f Int incInside = fmap (+ 1) and the same function using Scalaz: import scalaz._; import Scalaz._; def incInside[F[_]](x: F[Int])(implicit fn: Functor[F]): F[Int] = fn.fmap(x, (_:Int) + 1); I wonder: If you could choose (i.e. your favorite language would offer both), what would you pick - implicits or type classes? And what are your pros/cons?

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  • How do I write to an outer truecrypt volume when the inner volume protection prevents writng?

    - by con-f-use
    In a nutshell After some time using the outer volume of a hidden volume in Truecrypt I cannot write to the outer volume anymore. The protection of the inner volume always kicks in before. How do I fix this? Details I'm using truecrypt's two layered encryption of a USB stick. The outer container carries my semi-sensitive stuff while the inner hidden values has a bit more valuable information. I use both, the inner and outer volume regularly and that is part of the problem. Truecrypt can mount the outer volume for writing while protecting the inner. Usually the inner volume, when not protected this way (or mounted read-only) would be indistinguishable from free space. That is of course part of the plausible deniability scheme of truecrypt. At the beginning, everything worked as expected. I could copy and delete data to the outer volume as I pleased. Now it seams that I have written and deleted enough data to have filled the outer volume once. Despite the write protection Ubuntu tries now to write to the continuous "free space" that is the inner volume. It does that although enough other free space is on the outer volume. But on this free space there used to be data so its fragmented and the file system write prefers continuous space. The write on the continuous free space of the outer volume of course fails (with the error message in the picture above) as Truecrypt's inner-volume-protection kicks in. The Question I know this is expected behaviour, but is there a better way to write to the outer volume that does not attempt to write to the hidden free space at the end? The whole question could be more generally rephrased to: How do I control, where on a partition data is written in Ubuntu?

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  • Using CSS Classes for individual effects - opinions?

    - by Cool Hand Luke UK
    Hey, Just trying to canvas some opinions here. I was wondering how people go about adding individual effects to html elements. Take this example: you have three types of h1 titles all the same size but some are black some are gold and some are white. Some have a text-shadow etc. Would you create separate CSS classes and add them do the h1 tag or would you create a new single class for each different h1 title type (with grouped CSS elements)? With singular class for each effect you can build up combos of classes in html class="gold shadow" but also how would you name them. For example its bad practice to give classes and id names associated to colours, because it doesn't define what it does well. However is this ok with textual CSS classes? Just wondering what others do, I know there are no hard and fast rules. Cheers.

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  • Return pointer to nested inner class from generic outer class

    - by helixed
    I'm new to C++, so bear with me. I have a generic class called A. A has a nested class called B. A contains a method called getB(), which is supposed to return a new instance of B. However, I can't get my code to compile. Here's what it looks like:#include A.h template <class E> class A { public: class B { public: int data; }; B * getB(); }; A.cpp #include "A.h" template <class E> A<E>::B * A::getB() { return new B(); } When I try to compile this, I get the following error: error: expected constructor, destructor, or type conversion before '*' token Does anybody know what I'm doing wrong? Thanks, helixed

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  • Using CSS Classes for indivdual effects - opinions?

    - by Cool Hand Luke UK
    Hey, Just trying to canvas some opinions here. I was wondering how people go about adding individual effects to html elements. Take this example: you have three types of h1 titles all the same size but some are black some are gold and some are white. Some have a text-shadow etc. Would you create separate CSS classes and add them do the h1 tag or would you create a new single class for each different h1 title type (with grouped CSS elements)? With singular class for each effect you can build up combos of classes in html class="gold shadow" but also how would you name them. For example its bad practice to give classes and id names associated to colours, because it doesn't define what it does well. However is this ok with textual CSS classes? Just wondering what others do, I know there are no hard and fast rules. Cheers.

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  • C# Sharp: Partial Classes

    - by dcolumbus
    This is quick confirmation question: In order to make partial classes work, I initially thought that there would be a main Class public class ManageDates and then you would create partial classes like public partial class ManageDates to extend the ManageDates class. But from some experiementing, I've come to find out that if you're going to use partial classes, each individual class must be declared public partial class [ClassName] ... Am I correct in this conclusion?

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  • Does C# support inner classes? [closed]

    - by Amy
    Possible Duplicates: Using Inner classes in C# Inner classes in C# Class declared inside of another class in C# Does C# support the concept of inner classes? If so, what are the benefits? Could someone please explain this to me?

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  • Another question about ASP.NET MVC and a separate project for helper classes

    - by rockinthesixstring
    I know this topic has been discussed to death, but there is one thing that I can't wrap my head around. I'm working on a Web Application using ASP.NET MVC and I come across a scenario where I need a helper class (this usually happens in the early stages of development. So I go ahead and create a helper project in my solution that I use to manage all of my Helper Classes. Now, do I have to build that project and dump the dll in the bin directory every time I make changes to is, or is there a way to have the main web application reference the classes contained within the separate project without the separate build process? I'm just looking for the easiest way to add helper classes without the hastel of building and moving the dll every time I make a change or addition. Also, sorry for the very newbie-esque question here. All of the web apps I've build in the past have all been in the same project (web forms, App_Code, etc).

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  • Json Jackson deserialization without inner classes

    - by Eto Demerzel
    Hi everyone, I have a question concerning Json deserialization using Jackson. I would like to deserialize a Json file using a class like this one: (taken from http://wiki.fasterxml.com/JacksonInFiveMinutes) public class User { public enum Gender { MALE, FEMALE }; public static class Name { private String _first, _last; public String getFirst() { return _first; } public String getLast() { return _last; } public void setFirst(String s) { _first = s; } public void setLast(String s) { _last = s; } } private Gender _gender; private Name _name; private boolean _isVerified; private byte[] _userImage; public Name getName() { return _name; } public boolean isVerified() { return _isVerified; } public Gender getGender() { return _gender; } public byte[] getUserImage() { return _userImage; } public void setName(Name n) { _name = n; } public void setVerified(boolean b) { _isVerified = b; } public void setGender(Gender g) { _gender = g; } public void setUserImage(byte[] b) { _userImage = b; } } A Json file can be deserialized using the so called "Full Data Binding" in this way: ObjectMapper mapper = new ObjectMapper(); User user = mapper.readValue(new File("user.json"), User.class); My problem is the usage of the inner class "Name". I would like to do the same thing without using inner classes. The "User" class would became like that: import Name; import Gender; public class User { private Gender _gender; private Name _name; private boolean _isVerified; private byte[] _userImage; public Name getName() { return _name; } public boolean isVerified() { return _isVerified; } public Gender getGender() { return _gender; } public byte[] getUserImage() { return _userImage; } public void setName(Name n) { _name = n; } public void setVerified(boolean b) { _isVerified = b; } public void setGender(Gender g) { _gender = g; } public void setUserImage(byte[] b) { _userImage = b; } } This means to find a way to specify to the mapper all the required classes in order to perform the deserialization. Is this possible? I looked at the documentation but I cannot find any solution. My need comes from the fact that I use the Javassist library to create such classes, and it does not support inner or anonymous classes. Thank you in advance

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  • multiple classes with same methods - best pattern

    - by Tony
    I have a few classes in my current project where validation of Email/Website addresses is necessary. The methods to do that are all the same. I wondered what's the best way to implement this, so I don't need to have these methods copy pasted everywhere? The classes themselves are not necessarily related, they only have those validation methods in common.

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  • Help required in adding new methods, properties into existing classes dynamically

    - by Bepenfriends
    Hi All, I am not sure whether it is possible to achieve this kind of implementation in Dot Net. Below are the information Currently we are on an application which is done in COM+, ASP, XSL, XML technologies. It is a multi tier architecture application in which COM+ acts as the BAL. The execution steps for any CRUD operation will be defined using a seperate UI which uses XML to store the information. BAL reads the XML and understands the execution steps which are defined and executes corresponding methods in DLL. Much like EDM we have our custom model (using XML) which determines which property of object is searchable, retrievable etc. Based on this information BAL constructs queries and calls procedures to get the data. In the current application both BAL and DAL are heavily customizable without doing any code change. the results will be transmitted to presentation layer in XML format which constructs the UI based on the data recieved. Now I am creating a migration project which deals with employee information. It is also going to follow the N Tier architecture in which the presentation layer communicates with BAL which connects to DAL to return the Data. Here is the problem, In our existing version we are handling every information as XML in its native form (no converstion of object etc), but in the migration project, Team is really interested in utilizing the OOP model of development where every information which is sent from BAL need to be converted to objects of its respective types (example employeeCollection, Address Collection etc). If we have the static number of data returned from BAL we can have a class which contains those nodes as properties and we can access the same. But in our case the data returned from our BAL need to be customized. How can we handle the customization in presentation layer which is converting the result to an Object. Below is an example of the XML returned <employees> <employee> <firstName>Employee 1 First Name</firstName> <lastName>Employee 1 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>3</addressType> <StreetName>Street name3</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> <employee> <firstName>Employee 2 First Name</firstName> <lastName>Employee 2 Last Name</lastName> <addresses> <address> <addressType>1</addressType> <StreetName>Street name1</StreetName> <RegionName>Region name</RegionName> <address> <address> <addressType>2</addressType> <StreetName>Street name2</StreetName> <RegionName>Region name</RegionName> <address> <addresses> </employee> </employees> If these are the only columns then i can write a class which is like public class Address{ public int AddressType {get;set;}; public string StreetName {get;set;}; public string RegionName {get;set;}; } public class Employee{ public string FirstName {get; set;} public string LastName {get; set;} public string AddressCollection {get; set;} } public class EmployeeCollection : List<Employee>{ public bool Add (Employee Data){ .... } } public class AddressCollection : List<Address>{ public bool Add (Address Data){ .... } } This class will be provided to customers and consultants as DLLs. We will not provide the source code for the same. Now when the consultants or customers does customization(example adding country to address and adding passport information object with employee object) they must be able to access those properties in these classes, but without source code they will not be able to do those modifications.which makes the application useless. Is there is any way to acomplish this in DotNet. I thought of using Anonymous classes but, the problem with Anonymous classes are we can not have methods in it. I am not sure how can i fit the collection objects (which will be inturn an anonymous class) Not sure about datagrid / user control binding etc. I also thought of using CODEDom to create classes runtime but not sure about the meory, performance issues. also the classes must be created only once and must use the same till there is another change. Kindly help me out in this problem. Any kind of help meterial/ cryptic code/ links will be helpful.

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  • PHP: Aggregate Model Classes or Uber Model Classes?

    - by sunwukung
    In many of the discussions regarding the M in MVC, (sidestepping ORM controversies for a moment), I commonly see Model classes described as object representations of table data (be that an Active Record, Table Gateway, Row Gateway or Domain Model/Mapper). Martin Fowler warns against the development of an anemic domain model, i.e. a class that is nothing more than a wrapper for CRUD functionality. I've been working on an MVC application for a couple of months now. The DBAL in the application I'm working on started out simple (on account of my understanding - oh the benefits of hindsight), and is organised so that Controllers invoke Business Logic classes, that in turn access the database via DAO/Transaction Scripts pertinent to the task at hand. There are a few "Entity" classes that aggregate these DAO objects to provide a convenient CRUD wrapper, but also embody some of the "behaviour" of that Domain concept (for example, a user - since it's easy to isolate). Taking a look at some of the code, and thinking along refactoring some of the code into a Rich Domain Model, it occurred to me that were I to try and wrap the CRUD routines and behaviour of say, a Company into a single "Model" class, that would be a sizeable class. So, my question is this: do Models represent domain objects, business logic, service layers, all of the above combined? How do you go about defining the responsibilities for these components?

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  • How to refactor a myriad of similar classes

    - by TobiMcNamobi
    I'm faced with similar classes A1, A2, ..., A100. Believe it or not but yeah, there are roughly hundred classes that almost look the same. None of these classes are unit tested (of course ;-) ). Each of theses classes is about 50 lines of code which is not too much by itself. Still this is way too much duplicated code. I consider the following options: Writing tests for A1, ..., A100. Then refactor by creating an abstract base class AA. Pro: I'm (near to totally) safe by the tests that nothing goes wrong. Con: Much effort. Duplication of test code. Writing tests for A1, A2. Abstracting the duplicated test code and using the abstraction to create the rest of the tests. Then create AA as in 1. Pro: Less effort than in 1 but maintaining a similar degree of safety. Con: I find generalized test code weird; it often seems ... incoherent (is this the right word?). Normally I prefer specialized test code for specialized classes. But that requires a good design which is my goal of this whole refactoring. Writing AA first, testing it with mock classes. Then inheriting A1, ..., A100 successively. Pro: Fastest way to eliminate duplicates. Con: Most Ax classes look very much the same. But if not, there is the danger of changing the code by inheriting from AA. Other options ... At first I went for 3. because the Ax classes are really very similar to each other. But now I'm a bit unsure if this is the right way (from a unit testing enthusiast's perspective).

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  • JAVA Classes in Game programming.

    - by Gabriel A. Zorrilla
    I'm doing a little strategy game to help me learn Java in a fun way. The thing is I visioned the units as objects that would self draw on the game map (using images and buffering) and would react to the mouse actions with listeners attached to them. Now, based on some tutorials I've been reading regarding basic game programming, all seems to be drawn in the Graphics method of my Map class. If a new unit emerges, i just update the Map.Graphics method, it's not as easy as making a new Unit object which would self draw... In this case, I'd be stuck with a whole bunch of Map methods instead of using classes for rendering new things. So my question is, is it possible to use classes for rendering units, interface objects, etc, or i'll have to create methods and just do some kind of structural programming instead of object oriented? I'm a little bit confused and I'd like to have a mental blueprint of how things would be organized. Thanks!

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  • Equivalence Classes

    - by orcik
    I need to write a program for equivalence classes and get this outputs... (equiv '((a b) (a c) (d e) (e f) (c g) (g h))) => ((a b c g h) (d e f)) (equiv '((a b) (c d) (e f) (f g) (a e))) => ((a b e f g) (c d)) Basically, A set is a list in which the order doesn't matter, but elements don't appear more than once. The function should accept a list of pairs (elements which are related according to some equivalence relation), and return a set of equivalence classes without using iteration or assignment statements (e.g. do, set!, etc.). However, set utilities such as set-intersection, set-union and a function which eliminates duplicates in a list and built-in functions union, intersection, and remove-duplicates are allowed. Thanks a lot! By the way, It's not a homework question. A friend of mine need this piece of code to solve smilar questions.

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  • Problem with Classes in Python..

    - by Gui
    Ok guys, I'm really new at python (and programming itself) so sorry for my ignorance, but I really needed to ask this. So im doing a wxPython project where I added several tabs for a notebook (each tab of the notebook = a class) and there is one tab where I added a checkbox (in a tab, lets call it for example Tab1), and what I want is that when someone checks it, a button that exists in other tab (class called for example tab2) gets hidden where previously it was being shown. Well I see that it isn't hard to accomplish this, but my problem is the classes (tab1 and tab2, in this example). I've been trying to figure it out by searching but I guess im not searching hard enough because I just can't get it right. If they were in the same class I wouldn't have a problem, but as they are in different classes, im having a huge struggle with this. Hope someone can help me, and sorry for my ignorance once again.

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  • Events in Classes (VB.NET)

    - by Otaku
    I find that I write a lot of code within my classes to keep properties in sync with each other. I've read about Events in Classes, but have not been able to wrap my head around how to make them work for what I'm looking for. I could use some advice here. For example, in this one I always want to keep myColor up to date with any change whatsoever in any or all of the Red, Green or Blue properties. Class myColors Private Property Red As Byte Private Property Green As Byte Private Property Blue As Byte Private Property myColor As Color Sub New() myColor = Color.FromArgb(0, 0, 0) End Sub Sub ChangeRed(ByVal r As Byte) Red = r myColor = Color.FromArgb(Red, Green, Blue) End Sub Sub ChangeBlue(ByVal b As Byte) Blue = b myColor = Color.FromArgb(Red, Green, Blue) End Sub End Class If one or more of those changes, I want myColor to be updated. Easy enough as above, but is there a way to work with events that would automatically do this so I don't have to put myColor = Color.FromArgb(Red, Green, Blue) in every sub routine?

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  • Equivalence Classes LISP

    - by orcik
    I need to write a program for equivalence classes and get this outputs... (equiv '((a b) (a c) (d e) (e f) (c g) (g h))) => ((a b c g h) (d e f)) (equiv '((a b) (c d) (e f) (f g) (a e))) => ((a b e f g) (c d)) Basically, A set is a list in which the order doesn't matter, but elements don't appear more than once. The function should accept a list of pairs (elements which are related according to some equivalence relation), and return a set of equivalence classes without using iteration or assignment statements (e.g. do, set!, etc.). However, set utilities such as set-intersection, set-union and a function which eliminates duplicates in a list and built-in functions union, intersection, and remove-duplicates are allowed. Thanks a lot!

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