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  • Linking/Combining Type Classes in Haskell

    - by thegravian
    Say I have two type classes defined as follows that are identical in function but different in names: class Monad m where (>>=) :: m a -> (a -> m b) -> m b return :: a -> m a class PhantomMonad p where pbind :: p a -> (a -> p b) -> p b preturn :: a -> p b Is there a way to tie these two classes together so something that is an instance of PhantomMonad will automatically be an instance of Monad, or will instances for each class have to be explicitly written? Any insight would be most appreciated, thanks!

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  • How do I find all the datetimes that happen on a particular date in ruby?

    - by Angela
    I have a method which goes through each day of the week: def dates_week(d, delim) "<tr>" + (d.beginning_of_week...(d.beginning_of_week+5)).map do |day| "<#{delim}> #{yield(day)} </#{delim}>" end.join + "</tr>" end For each day of the week, I plug that as an arg into a method (or maybe a named_scope, haven't figured out which), that will then output the .count for :all the emails that have a :date_sent on that date. However, :date_sent is a date-timestamp, so I can't use == as I have below. def sent_emails_by_date(date) ContactEmail.find(:all, :conditions => "date_sent = '#{date}'" " ).count end How do I find all the emails that fall on the day for the date passed through from the method which loops through a week as shown above?

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  • Android sql creating database once

    - by semajhan
    One thing i'm not understanding is how to create the database and data just once in an android application. I extend SQLiteOpenHelper and use a DataHelper class that to manipulate data. Now, I have addEvent() and updateEvent() within the DataHelper class. I create an instance of DataHelper in my Activity and addEvent() a couple of times to insert data. Well, now I don't know how to just do that once. If I restart the app, its just going to "addEvent()" again and so the data is being reset every time. Sorry for the probably really REALLY noob question. The only solution I found was not using the DataHelper class and just adding data "manually" within the onCreate() method in SQLiteOpenHelper.

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  • C++ String pointers

    - by gnm
    In my previous app I had an object like this: class myType { public: int a; string b; } It had a lot of instances scattered everywhere and passed around to nearly every function. The app was slow. Profiling said that 95% of time is eaten by the string allocator function. I know how to work with the object above, but not how to work with string pointers. class myType { public: int a; string* b; } They told me to use pointers as above. How much faster is it with a string pointer? What is copied when I copy the object? How to the following using the class with the pointer: Access the string value Modify the string value without modifying the one in the object (copy?) General things that change if I use string pointers?

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  • save object associate to another object automatically

    - by Luca Romagnoli
    Hi i have these classes: class Core < ActiveRecord::Base belongs_to :resource, :polymorphic => true belongs_to :image, :class_name => 'Multimedia', :foreign_key => 'image_id' end class Place < ActiveRecord::Base has_one :core, :as => :resource end If i try do launch this: a = Place.find(5) a.name ="a" a.core.image_id = 24 a.save name is saved. image_id no i want save automatically all changes in records in relationship with place class at a.save command. is possible? thanks

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  • Which is the best and appropriate way to write the code in Winforms ?

    - by Harikrishna
    What is the best way to write the code ? (1) Like directly writing the code in the button_click() event. or (2) Make the function of that code which I write in button_click() event and write this function in one class and then that function I should call in the button_Click() event.Like is it called three-tired approach to write the code ? Like in button_Click() event I write the code to save the records in csv file from datatable.So I should write that code in button_Click() event or I should make one new function and one new class and write that code in that function which is the new class and calling that function in button_Click() event. This is only one example but I am talking about all the code written in my application that which is the appropriate and best way to write the code and what are the benefits ? Note that I write the code in Winforms with c#.

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  • Android: Referring to a string resource when defining a log name

    - by spookypeanut
    In my Android app, I want to use a single variable for the log name in multiple files. At the moment, I'm specifying it separately in each file, e.g. public final String LOG_NAME = "LogName"; Log.d(LOG_NAME, "Logged output); I've tried this: public final String LOG_NAME = (String) getText(R.string.app_name_nospaces); And while this works in generally most of my files, Eclipse complains about one of them: The method getText(int) is undefined for the type DatabaseManager I've made sure I'm definitely importing android.content.Context in that file. If I tell it exactly where to find getText: Multiple markers at this line - Cannot make a static reference to the non-static method getText(int) from the type Context - The method getText(int) is undefined for the type DatabaseManager I'm sure I've committed a glaringly obvious n00b error, but I just can't see it! Thanks for all help: if any other code snippets would help, let me know.

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  • Where do you hang your semantic information, html?

    - by bobobobo
    Well, I keep putting semantic information about what an element means for the page logically in the class attribute <li class="phone-number">555-5555</li> It seems to work for this dual purpose of hanging semantic information and a pointer to how to style it. I'm not sure if this is the best idea, I'm trying to see if others have other ways of doing it. I also started to use a hidden input: <li>555-5555 <input class="semantics" type="hidden" value="phone-number" /></li> inside an element, so with jQuery, I can retrieve additional information about the element using li.find( '.semantics' ).val() To get an element's semantics from JavaScript

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  • Loop through collections

    - by ScG
    I have two classes class A { public string something { get; set; } public IList<B> b= new List<B>(); } class B { public string else { get; set; } public string elseelse { get; set; } } I have populated an object of class A called obj. How can I loop through this object and print values. Do I have to use two foreach's like the one show here or is there a better way? foreach (var z in obj) { // print z.something; foreach (var x in z.b) { // print x.elseelse; } }

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  • C++: Throwing shared_ptr of derived and catching shared_ptr of base?

    - by hasvn
    Ok, I've been told this problem: Why can you throw a pointer to a derived class and catch a pointer to its base... but you can't do that with shared_ptrs? Example, this works: class Base {}; class Derived : public Base {}; int main() { try { throw new Derived() ; } catch( const Base2 * b ) { printf("Received a base" ) ; } return 0 ; } But this doesn't int main() { try { throw std::tr1::shared_ptr<Derived>( new Derived() ) ; } catch( const std::tr1::shared_ptr<Base> & b ) { printf("Received a base" ) ; } return 0 ; } Any ideas?

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  • In TDD, should tests be written by the person who implemented the feature under test?

    - by martin
    We run a project in which we want to solve with test driven development. I thought about some questions that came up when initiating the project. One question was: Who should write the unit-test for a feature? Should the unit-test be written by the feature-implementing programmer? Or should the unit test be written by another programmer, who defines what a method should do and the feature-implementing programmer implements the method until the tests runs? If I understand the concept of TDD in the right way, the feature-implementing programmer has to write the test by himself, because TDD is procedure with mini-iterations. So it would be too complex to have the tests written by another programmer? What would you say? Should the tests in TDD be written by the programmer himself or should another programmer write the tests that describes what a method can do?

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  • Java how to load modules

    - by gerardorn
    heres my problem: im building a server that loads modules. each module is a .jar file. inside the jar theres all the classes that the module need. the server needs to read the jar, find the main class (it doesnt have the main method on it is just the class that makes the module work but not as a different program), build an object of that class and store it in a vector of modules so that it can acces to a specific module depending on the job to be done. how can i do that? as far as the server, it is listening and reciving request, but thes no modules to delegate the job to, since my vector of modules is empty

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  • Make jquery array out of div

    - by Industrial
    Hi everyone, Each div with the class "row" is added upon request from the user, to be able to add multiple items at once. So now is the question how I'll collect all the forms in to an array that PHP can read (like JSON for instance). I'll guess that there's already some easy and effective way of doing this? <div class="container"> <div class="row"> <input type="text" name="value1" id="textfield" /> <input type="text" name="value2" id="textfield" /> <input type="text" name="value3" id="textfield" /> </div> </div> Here's what I would like to achieve out of the shown example: array( array ('value1' => '', 'value2' => '', 'value3' => '') ); Thanks!

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  • how to add multiple modules to a single page in digitalus

    - by jspeshu
    when i do some thing like this i can see the module <div id='search' class="module"> <digitalusControl type='moduleSelector' id='module' label="searchM" group='mods' /> </div> but i want to have two modules so i make something like this <div id='search' class="module"> <digitalusControl type='moduleSelector' id='modulesearch' label="searchM" group='mods' /> </div> <div id='search' class="module"> <digitalusControl type='moduleSelector' id='modulenews' label="newsM" group='mods' /> </div> plz help how can i create multiple modules since i can't create another element "digitalusControl" with id "module" i really need this plz help EDIT: even worse a template with only one module, this single line is not working for me

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  • When and why does an EventHandler require objects to be final?

    - by Michiel Borkent
    I have the following code from a GWT Project that is part of the onModuleLoad() method (similar to Java's main method, if you don't know GWT): final TextBox t1 = new TextBox(); final Label lt1 = new Label(); t1.addKeyUpHandler(new KeyUpHandler() { @Override public void onKeyUp(KeyUpEvent event) { // TODO Auto-generated method stub if (!(t1.getText().matches("\\w{2}-\\w{2}-\\w{2}"))) lt1.setText("Invalid."); else lt1.setText("OK."); } }); Why do the two local variables have to be final here?

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  • where to put business logic in a library?

    - by fayer
    i'm going to create a library that consists of a lot of separate classes. i'm very familiar with mvc but have never created a pure library before. i wonder where i should put the business logic? the logic that is in the controller in a mvc. should it be in a class? or in a "bootstrap" file? and should one file include every class, or should only one class include its classes it uses? thanks!

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  • Is correct name enough to make it happen?

    - by Knowing me knowing you
    Guys, I've just dipped in to limits.h by MS. I tried to check what's the return type for max() fnc and to my surprise I see something like this: // TEMPLATE CLASS numeric_limits template<class _Ty> class numeric_limits : public _Num_base { // numeric limits for arbitrary type _Ty (say little or nothing) public: static _Ty (__CRTDECL min)() _THROW0() { // return minimum value return (_Ty(0)); } static _Ty (__CRTDECL max)() _THROW0() { // return maximum value return (_Ty(0));//EXACTLY THE SAME WHAT IN min<<------------------ } //... other stuff }; so how is it possiple that in both min and max return does exactly the same? So does it mean if I would write makeSanwich() return (_Ty(0)) it would make a sandwich for me? How is it possible that having this same code just fnc names different we are getting different results?

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  • Declared Properties and assigning values with self

    - by Shaun Budhram
    I understand how declared properties work - I just need a clarification on when Objective C is using the accessor method vs. when it is not. Say I have a property declared using retain: @property (nonatomic, retain) NSDate *date; ... and later... @synthesize date If I say: date = x Is that calling the accessor method? Or is it just setting the variable? self.date = x This seems to call the accessor method (I think but I'm not sure, since it seems like the retain count is increasing). Can anyone clarify this issue? I'm curious because i have some variables that seem to become invalid before I need them (and I have to specifically call retain), and I suspect this is why.

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  • what happen if I delete the xx.jar file after I started to execute the xx.jar

    - by ogzylz
    I have a server program running a java binary code (xx.jar file) While it is running I erranously delete the xx.jar file. The program continues to run. But I am not sure if the results will be correct, and I am not sure if the program will fail? When I delete the xx.jar file, the program was in a method for a long time and still it is in that method call. When it calls another method call will my program fail? I am asking this question because If deleting the file has no harm I will be gaining about 3-4h on a server machine

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  • Prototype - DOM Traversal with up()

    - by Jason McCreary
    I have the following structure: <form> <div class="content"> ... </div> <div class="action"> <p>Select <a class="select_all" href="?select=1" title="Select All">All</a></p> </div> </form> I am using Prototype's up() to traverse the DOM in order to find the <form> element in respect to the a.select_all. However the following doesn't work: select_link.up('form'); // returns undefined Yet, this does. select_link.up().up().up(); // returns HTMLFormElement Clearly this is an ancestor of a.select_all. The API Docs state Element.up() supports a CSSRule. What am I missing here?

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  • Are static members inherited? (C++)

    - by Keand64
    When static members are inherited, are they static for the entire heirarchy, or just that class, ie: class SomeClass { public: SomeClass(){total++;} static int total; }; class SomeDerivedClass: public SomeClass { public: SomeDerivedClass(){total++;} }; int main() { SomeClass A; SomeClass B; SomeDerivedClass C; return 0; } would total be 3 in all three instances, or would it be 2 for SomeClass and 1 for SomeDerivedClass?

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  • Global Import/using Aliasing in .NET

    - by Josh Stodola
    Using import aliasing in a single class, we can reference class library namespaces by assigning our own custom alias like this: ' VB Imports Db = Company.Lib.Data.Objects // C# using Db = Company.Lib.Data.Objects; And then we are able to reference the classes inside of Company.Lib.Data.Objects by using the Db alias that we assigned. Is it possible to do this at the global level so that the alias is applied to the entire solution instead of the given file? Currently, we are working with web applications, so I was hoping we could add something to web.config, but I am also interested in whether or not this is possible with windows forms, console apps, and/or class libraries.

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  • Is it possible to select data with max value for a column using Criteria in Hibernate?

    - by Palo
    Lets say I have the following mapping: <hibernate-mapping package="mypackage"> <class name="User" table="user"> <id name="id" column="id"> <generator class="native"></generator> </id> <property name="name" /> <property name="age" /> </class> </hibernate-mapping> Is it possible to select the oldest user (that is age is maximal) using Criteria in Hibernate? I can imagine that i could do this with 2 selects. (first select total number of users and then order the entries descending by age and select the first entry). But is it possible with a single select? Thank you Palo

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  • Keeping track of threads when creating them recursively

    - by 66replica
    I'm currently working on some code for my Programming Languages course. I can't post the code but I'm permitted to talk about some high level concepts that I'm struggling with and receive input on them. Basically the code is a recursive DFS on a undirected graph that I'm supposed to convert to a concurrent program. My professor already specified that I should create my threads in the recursive DFS method and then join them in another method. Basically, I'm having trouble thinking of how I should keep track of the threads I'm creating so I can join all of them in the other method. I'm thinking an array of Threads but I'm unsure how to add each new thread to the array or even if that's the right direction.

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  • Using template specialization in C++

    - by user550413
    How can I write a function using template specialization that has 2 different input types and an output type: template <class input1, class input2, class output> and return the sum of the 2 numbers (integers/doubles). However, if I get 2 integers I want to return an integer type but for any other combinations of integer and double I'll always return double. I am trying to do that without using directly the '+' operator but having the next functions instead: double add_double_double(double a, double b) {return (a+b);} double add_int_double(int a, double b) {return ((double)(a)+b);} int add_int_int(int a, int b) {return (a+b);}

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