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  • How do I find the user that has both a cat and a dog?

    - by brad
    I want to do a search across 2 tables that have a many-to-one relationship, eg class User << ActiveRecord::Base has_many :pets end class Pet << ActiveRecord::Base belongs_to :users end Now let's say I have some data like so users id name 1 Bob 2 Joe 3 Brian pets id user_id animal 1 1 cat 2 1 dog 3 2 cat 4 3 dog What I want to do is create an active record query that will return a user that has both a cat and a dog (i.e. user 1 - Bob). My attempt at this so far is User.joins(:pets).where('pets.animal = ? AND pets.animal = ?','dog','cat') Now I understand why this doesn't work - it's looking for a pet that is both a dog and a cat so returns nothing. I don't know how to modify this to give me the answer I want however. Does anyone have any suggestions? This seems like it should be easy - it doesn't seem like an especially unusual situation.

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  • Fedora 12 Wireless problems (Intel Wireless 4965AGN Card)

    - by Ninefingers
    Hi All, I'm having an interesting experience with my wireless card at the moment. Basically, it does like this: I connect to the local wireless network (netgear router) It works, briefly, allowing me to browse a webpage or maybe two, if I'm lucky. It then stops working / sending any packets, whilst reported still connected. Now, me being me I've had a look to see what I can find. wpa_supplicant.log looks like this: Trying to associate with valid_mac:a2:30 (SSID='vennardwireless' freq=2462 MHz) Associated with valid_mac:a2:30 WPA: Key negotiation completed with valid_mac:a2:30 [PTK=CCMP GTK=TKIP] CTRL-EVENT-CONNECTED - Connection to valid_mac:a2:30 completed (reauth) [id=0 id_str=] CTRL-EVENT-DISCONNECTED - Disconnect event - remove keys So that's working fine. dmesg | grep "*iwl*" spits out this: iwlagn: Intel(R) Wireless WiFi Link AGN driver for Linux, 1.3.27kds iwlagn: Copyright(c) 2003-2009 Intel Corporation iwlagn 0000:03:00.0: PCI INT A -> GSI 17 (level, low) -> IRQ 17 iwlagn 0000:03:00.0: setting latency timer to 64 iwlagn 0000:03:00.0: Detected Intel Wireless WiFi Link 4965AGN REV=0x4 iwlagn 0000:03:00.0: Tunable channels: 13 802.11bg, 19 802.11a channels iwlagn 0000:03:00.0: irq 32 for MSI/MSI-X phy0: Selected rate control algorithm 'iwl-agn-rs' iwlagn 0000:03:00.0: firmware: requesting iwlwifi-4965-2.ucode iwlagn 0000:03:00.0: loaded firmware version 228.61.2.24 Registered led device: iwl-phy0::radio Registered led device: iwl-phy0::assoc Registered led device: iwl-phy0::RX Registered led device: iwl-phy0::TX iwlagn 0000:03:00.0: iwl_tx_agg_start on ra = 00:24:b2:32:a3:30 tid = 0 iwlagn 0000:03:00.0: iwl_tx_agg_start on ra = 00:24:b2:32:a3:30 tid = 0 So that's working too. I can also ping 192.168.0.1 -I wlan0 and arping 192.168.0.1 -I wlan0 the router until the network falls over. uname -r:2.6.32.10-90.fc12.x86_64. Laptop is a Core2 Duo (2Ghz) with 3GB RAM. Other symptoms I've noticed are that wireshark freezes when I capture on the "broken" interface until I disconnect. Am using networkmanager as per normal. Stupidly, I can connect to the same router via eth0/a cat6 cable just fine. Everyone else can connect to the AP fine (from Windows). Yes, I'm sat right next to it and not trying to access a hotspot the other side of the world. Any ideas? Is this a broken update? (I intend to reboot and test an older kernel later)? Anyone else come across this? Edit: iwconfig wlan0 rate auto is the settings I'm using for rates. Also, according to networkmanager the network is still connected. Thanks for any pointers / advice.

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  • operator+ overload returning object causing memory leaks, C++

    - by lampshade
    The problem i think is with returing an object when i overload the + operator. I tried returning a reference to the object, but doing so does not fix the memory leak. I can comment out the two statements: dObj = dObj + dObj2; and cObj = cObj + cObj2; to free the program of memory leaks. Somehow, the problem is with returning an object after overloading the + operator. #include <iostream> #include <vld.h> using namespace std; class Animal { public : Animal() {}; virtual void eat() = 0 {}; virtual void walk() = 0 {}; }; class Dog : public Animal { public : Dog(const char * name, const char * gender, int age); Dog() : name(NULL), gender(NULL), age(0) {}; virtual ~Dog(); Dog operator+(const Dog &dObj); private : char * name; char * gender; int age; }; class MyClass { public : MyClass() : action(NULL) {}; void setInstance(Animal &newInstance); void doSomething(); private : Animal * action; }; Dog::Dog(const char * name, const char * gender, int age) : // allocating here, for data passed in ctor name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Dog::~Dog() { delete name; delete gender; age = 0; } Dog Dog::operator+(const Dog &dObj) { Dog d; d.age = age + dObj.age; return d; } void MyClass::setInstance(Animal &newInstance) { action = &newInstance; } void MyClass::doSomething() { action->walk(); action->eat(); } int main() { MyClass mObj; Dog dObj("Scruffy", "Male", 4); // passing data into ctor Dog dObj2("Scooby", "Male", 6); mObj.setInstance(dObj); // set the instance specific to the object. mObj.doSomething(); // something happens based on which object is passed in dObj = dObj + dObj2; // invoke the operator+ return 0; }

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  • Have error message show when form is created through AJAX

    - by Railslearner
    I have a page called /add that you can add a Dog on and the form is in its own partial. I'm using Simple Form and Twitter Bootstrap. I added the files for the main Bootstrap but use a gem for simple_form to work with it just so you know. DogsController # new.js.erb (deleted new.html.erb) def new @dog = Dog.new respond_to do |format| format.js end end # create.js.erb def create @dog = current_user.dogs.new(params[:dog]) respond_to do |format| if @dog.save format.html { redirect_to add_url, notice: 'Dog was successfully added.' } format.json { render json: @dog, status: :created, location: @dog} format.js else format.html { render 'pages/add' } format.json { render json: @dog.errors, status: :unprocessable_entity } end end end dogs/_form.html.erb <%= simple_form_for(@dog, :remote => true) do |f| %> <%= render :partial => "shared/error_message", :locals => { :f => f } %> <%= f.input :name %> <%= f.button :submit, 'Done' %> <% end %> This line: <%= render :partial => "shared/error_message", :locals => { :f => f } %> Is for bootstrap so it renders the errors html correctly. PagesController def add respond_to do |format| format.html end end pages/add.html.erb <div id="generate-form"> </div> dogs/new.js.erb $("#generate-form").html("<%= escape_javascript(render(:partial => 'dogs/form', locals: { dog: @dog })) %>"); Now how would I get this to render the error partial as if it was still on my dogs/new.html.erb since its being created through AJAX? I don't need client side validations do I?

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  • PHP I am pulling my hair out trying to find the best! [closed]

    - by darga33
    PULLING MY HAIR OUT I have heard of Martin Fowler's book PoEAA and the other book Head First OOA OOD but those are not in PHP. I DESPERATELY WANT TO READ THEM, but ONLY in PHP utilizing SOLID principles! Does anyone know of the absolute best, most recent PHP book that utilizes the SOLID principles and GRASP, and all the other best practices? I want to learn from the best possible source! Not beginner books! I already understand OOP. This seems like an almost impossible question to find the answer to and so I thought, hey, might as well post on stackexchange!! Surely someone out there must know!!!!!!!!!! Or if noone knows Maybe they know of an open source application that utilizes these principles that is relatively small that is not a framework. Something that I can go through every single class, and spend time understanding the insides and outs of how the program was developed. Thanks so much in advance! I really really really really appreciate it!

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  • Sorting Table Cells based on data from NSArray

    - by Graeme
    Hi, I have an NSArray which contains information from an RSS feed on dogs, such as [dog types], [dog age] and [dog size]. At the moment my UITableView simply displays each cell on each dog and within the cell lists [dog types], [dog age] and [dog size]. I want to be able to allow users of my app to "sort" this data based on the dog name, dog size or dog age when they press a UIButton in the top nav-bar. I'm struggling to work out how to filter the UITableView based on these factors, so any help is appreciated. Thanks.

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  • Codeigniter/mySQL question. Checking if several inserts are possible before actual insertion.

    - by Ethan
    Hey SO, So I'm trying to perform a couple inserts at once that are kind of co-dependent on each other. Let's say I'm doing a dog rating website. Anyone can add a dog to my database, but in doing so they also need to add a preliminary rating of the dog. Other people can then rate the dog afterwards. The dogs to ratings is a many to one relationship: a dog has many ratings. This means for my preliminary add, since I have the person both rate and add the dog, I need to take the rating, and set a foreign key to the dog's primary key. As far as I know, this means I have to actually add the dog, then check what that new addition's primary key is, and then put that in my rating before insertion. Now suppose something were to go wrong with the rating's insert, be it a string that's too long, or something that I've overlooked somehow. If the rating's failed, the dog has already been inserted, but the rating has not. In this case, I'd like the dog to not have been added in the first place. Does this mean I have to write code that says "if the rating fails, do a remove for the dog," or is there a way to predict what the key will be for the dog should everything go as planned. Is there a way to say "hold that spot," and then if everything works, add it? Any help would be greatly appreciated. Thanks!!

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  • Should I allow sending complete structures when using PUT for updates in a REST API or not?

    - by dafmetal
    I am designing a REST API and I wonder what the recommended way to handle updates to resources would be. More specifically, I would allow updates through a PUT on the resource, but what should I allow in the body of the PUT request? Always the complete structure of the resource? Always the subpart (that changed) of the structure of the resource? A combination of both? For example, take the resource http://example.org/api/v1/dogs/packs/p1. A GET on this resource would give the following: Request: GET http://example.org/api/v1/dogs/packs/p1 Accept: application/xml Response: <pack> <owner>David</owner> <dogs> <dog> <name>Woofer</name> <breed>Basset Hound</breed> </dog> <dog> <name>Mr. Bones</name> <breed>Basset Hound</breed> </dog> </dogs> </pack> Suppose I want to add a dog (Sniffers the Basset Hound) to the pack, would I support either: Request: PUT http://example.org/api/v1/dogs/packs/p1 <dog> <name>Sniffers</name> <breed>Basset Hound</breed> </dog> Response: HTTP/1.1 200 OK or Request: PUT http://example.org/api/v1/dogs/packs/p1 <pack> <owner>David</owner> <dogs> <dog> <name>Woofer</name> <breed>Basset Hound</breed> </dog> <dog> <name>Mr. Bones</name> <breed>Basset Hound</breed> </dog> <dog> <name>Sniffers</name> <breed>Basset Hound</breed> </dog> </dogs> </pack> Response: HTTP/1.1 200 OK or both? If supporting updates through subsections of the structure is recommended, how would I handle deletes (such as when a dog dies)? Through query parameters?

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  • Rails after_create callback can't access model's attributes

    - by tybro0103
    I can't access my model's attributes in the after_create callback... seems like I should be able to right? controller: @dog = Dog.new(:color => 'brown', :gender => 'male') @dog.user_id = current_user.id @dog.save model: class Dog < ActiveRecord::Base def after_create logger.debug "[DOG CREATED] color:#{color} gender:#{gender} user:#{user_id}" end end console: (all seems well) >>Dog.last =>#<Dog id: 1, color: "brown", gender: "male", user_id: 1> log: (wtf!?) ... [DOG CREATED] color: gender:male user ... Some of my attributes show up and others don't! oh no! Anyone know what I'm doing wrong? I've always been able to user after_create in such ways in the past. Note: The actual variable names and values I used were different, but the methods and code are the same.

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  • Adding two different Objects by overloading operator+ C++

    - by lampshade
    Hello, I've been trying to figure out how to add a private member from Object A, to a private member from Object B. Both Cat and Dog Class's inheriate from the base class Animal. I have a thrid class 'MyClass', that I want to inheriate the private members of the Cat and Dog class. So in MyClass, I have a friend function to overload the + operator. THe friend function is defined as follows: MyClass operator+(const Dog &dObj, const Cat &cObj); I want to access dObj.age and cObj.age within the above function, invoke by this statement in main: mObj = dObj + cObj; Here is the entire source for a complete reference into the class objects: #include <iostream> #include <vld.h> using namespace std; class Animal { public : Animal() {}; virtual void eat() = 0 {}; virtual void walk() = 0 {}; }; class Dog : public Animal { public : Dog(const char * name, const char * gender, int age); Dog() : name(NULL), gender(NULL), age(0) {}; virtual ~Dog(); void eat(); void bark(); void walk(); private : char * name; char * gender; int age; }; class Cat : public Animal { public : Cat(const char * name, const char * gender, int age); Cat() : name(NULL), gender(NULL), age(0) {}; virtual ~Cat(); void eat(); void meow(); void walk(); private : char * name; char * gender; int age; }; class MyClass : private Cat, private Dog { public : MyClass() : action(NULL) {}; void setInstance(Animal &newInstance); void doSomething(); friend MyClass operator+(const Dog &dObj, const Cat &cObj); private : Animal * action; }; Cat::Cat(const char * name, const char * gender, int age) : name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Cat::~Cat() { delete name; delete gender; age = 0; } void Cat::walk() { cout << name << " is walking now.. " << endl; } void Cat::eat() { cout << name << " is eating now.. " << endl; } void Cat::meow() { cout << name << " says meow.. " << endl; } Dog::Dog(const char * name, const char * gender, int age) : name(new char[strlen(name)+1]), gender(new char[strlen(gender)+1]), age(age) { if (name) { size_t length = strlen(name) +1; strcpy_s(this->name, length, name); } else name = NULL; if (gender) { size_t length = strlen(gender) +1; strcpy_s(this->gender, length, gender); } else gender = NULL; if (age) { this->age = age; } } Dog::~Dog() { delete name; delete gender; age = 0; } void Dog::eat() { cout << name << " is eating now.. " << endl; } void Dog::bark() { cout << name << " says woof.. " << endl; } void Dog::walk() { cout << name << " is walking now.." << endl; } void MyClass::setInstance(Animal &newInstance) { action = &newInstance; } void MyClass::doSomething() { action->walk(); action->eat(); } MyClass operator+(const Dog &dObj, const Cat &cObj) { MyClass A; //dObj.age; //cObj.age; return A; } int main() { MyClass mObj; Dog dObj("B", "Male", 4); Cat cObj("C", "Female", 5); mObj.setInstance(dObj); // set the instance specific to the object. mObj.doSomething(); // something happens based on which object is passed in dObj.bark(); mObj.setInstance(cObj); mObj.doSomething(); cObj.meow(); mObj = dObj + cObj; return 0; }

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  • SQL to return the rownum of a specific row? (using Oracle db)

    - by jedierikb
    In Oracle 10g, I have this SQL: select dog.id as dogId from CANINES dog order by dog.codename asc which returns: id -- 204 203 206 923 I want to extend this query to determine the oracle rownum of a dog.id in this resultset. I have tried select rownum from (select dog.id as dogId from CANINES dog order by dog.codename asc) where dog.id=206 But this does not work out very well (it returns 1 no matter which dog.id I match on). I was expecting to get back 3. Thanks for your help! Notes http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html I am pretty sure I do not need to use rowid

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  • getting proxies of the correct type in nhibernate

    - by Nir
    I have a problem with uninitialized proxies in nhibernate The Domain Model Let's say I have two parallel class hierarchies: Animal, Dog, Cat and AnimalOwner, DogOwner, CatOwner where Dog and Cat both inherit from Animal and DogOwner and CatOwner both inherit from AnimalOwner. AnimalOwner has a reference of type Animal called OwnedAnimal. Here are the classes in the example: public abstract class Animal { // some properties } public class Dog : Animal { // some more properties } public class Cat : Animal { // some more properties } public class AnimalOwner { public virtual Animal OwnedAnimal {get;set;} // more properties... } public class DogOwner : AnimalOwner { // even more properties } public class CatOwner : AnimalOwner { // even more properties } The classes have proper nhibernate mapping, all properties are persistent and everything that can be lazy loaded is lazy loaded. The application business logic only let you to set a Dog in a DogOwner and a Cat in a CatOwner. The Problem I have code like this: public void ProcessDogOwner(DogOwner owner) { Dog dog = (Dog)owner.OwnedAnimal; .... } This method can be called by many diffrent methods, in most cases the dog is already in memory and everything is ok, but rarely the dog isn't already in memory - in this case I get an nhibernate "uninitialized proxy" but the cast throws an exception because nhibernate genrates a proxy for Animal and not for Dog. I understand that this is how nhibernate works, but I need to know the type without loading the object - or, more correctly I need the uninitialized proxy to be a proxy of Cat or Dog and not a proxy of Animal. Constraints I can't change the domain model, the model is handed to me by another department, I tried to get them to change the model and failed. The actual model is much more complicated then the example and the classes have many references between them, using eager loading or adding joins to the queries is out of the question for performance reasons. I have full control of the source code, the hbm mapping and the database schema and I can change them any way I want (as long as I don't change the relationships between the model classes). I have many methods like the one in the example and I don't want to modify all of them. Thanks, Nir

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  • How am i overriding this C++ inherited member function without the virtual keyword being used?

    - by Gary Willoughby
    I have a small program to demonstrate simple inheritance. I am defining a Dog class which is derived from Mammal. Both classes share a simple member function called ToString(). How is Dog overriding the implementation in the Mammal class, when i'm not using the virtual keyword? (Do i even need to use the virtual keyword to override member functions?) mammal.h #ifndef MAMMAL_H_INCLUDED #define MAMMAL_H_INCLUDED #include <string> class Mammal { public: std::string ToString(); }; #endif // MAMMAL_H_INCLUDED mammal.cpp #include <string> #include "mammal.h" std::string Mammal::ToString() { return "I am a Mammal!"; } dog.h #ifndef DOG_H_INCLUDED #define DOG_H_INCLUDED #include <string> #include "mammal.h" class Dog : public Mammal { public: std::string ToString(); }; #endif // DOG_H_INCLUDED dog.cpp #include <string> #include "dog.h" std::string Dog::ToString() { return "I am a Dog!"; } main.cpp #include <iostream> #include "dog.h" using namespace std; int main() { Dog d; std::cout << d.ToString() << std::endl; return 0; } output I am a Dog! I'm using MingW on Windows via Code::Blocks.

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  • Failed Castle ActiveRecord TransactionScope causes future queries to be invalid

    - by mbp
    I am trying to solve an issue when using a Castle ActiveRecord TransactionScope which is rolled back. After the rollback, I am unable to query the Dog table. The "Dog.FindFirst()" line fails with "Could not perform SlicedFindAll for Dog", because it cannot insert dogMissingName. using (new SessionScope()) { try { var trans = new TransactionScope(TransactionMode.New, OnDispose.Commit); try { var dog = new Dog { Name = "Snowy" }; dog.Save(); var dogMissingName = new Dog(); dogMissingName.Save(); } catch (Exception) { trans.VoteRollBack(); throw; } finally { trans.Dispose(); } } catch (Exception ex) { var randomDog = Dog.FindFirst() Console.WriteLine("Random dog : " + randomDog.Name); } } Stacktrace is as follows: Castle.ActiveRecord.Framework.ActiveRecordException: Could not perform SlicedFindAll for Dog ---> NHibernate.Exceptions.GenericADOException: could not insert: [Mvno.Dal.Dog#219e86fa-1081-490a-92d1-9d480171fcfd][SQL: INSERT INTO Dog (Name, Id) VALUES (?, ?)] ---> System.Data.SqlClient.SqlException: Cannot insert the value NULL into column 'Name', table 'Dog'; column does not allow nulls. INSERT fails. The statement has been terminated. ved System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection) ved System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception, Boolean breakConnection) ved System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj) ved System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj) ved System.Data.SqlClient.SqlCommand.FinishExecuteReader(SqlDataReader ds, RunBehavior runBehavior, String resetOptionsString) ved System.Data.SqlClient.SqlCommand.RunExecuteReaderTds(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, Boolean async) ved System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) ved System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result, String methodName, Boolean sendToPipe) ved System.Data.SqlClient.SqlCommand.ExecuteNonQuery() ved NHibernate.AdoNet.AbstractBatcher.ExecuteNonQuery(IDbCommand cmd) ved NHibernate.AdoNet.NonBatchingBatcher.AddToBatch(IExpectation expectation) ved NHibernate.Persister.Entity.AbstractEntityPersister.Insert(Object id, Object[] fields, Boolean[] notNull, Int32 j, SqlCommandInfo sql, Object obj, ISessionImplementor session) --- End of inner exception stack trace --- ved NHibernate.Persister.Entity.AbstractEntityPersister.Insert(Object id, Object[] fields, Boolean[] notNull, Int32 j, SqlCommandInfo sql, Object obj, ISessionImplementor session) ved NHibernate.Persister.Entity.AbstractEntityPersister.Insert(Object id, Object[] fields, Object obj, ISessionImplementor session) ved NHibernate.Action.EntityInsertAction.Execute() ved NHibernate.Engine.ActionQueue.Execute(IExecutable executable) ved NHibernate.Engine.ActionQueue.ExecuteActions(IList list) ved NHibernate.Engine.ActionQueue.ExecuteActions() ved NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session) ved NHibernate.Event.Default.DefaultAutoFlushEventListener.OnAutoFlush(AutoFlushEvent event) ved NHibernate.Impl.SessionImpl.AutoFlushIfRequired(ISet`1 querySpaces) ved NHibernate.Impl.SessionImpl.List(CriteriaImpl criteria, IList results) ved NHibernate.Impl.CriteriaImpl.List(IList results) ved NHibernate.Impl.CriteriaImpl.List() ved Castle.ActiveRecord.ActiveRecordBase.SlicedFindAll(Type targetType, Int32 firstResult, Int32 maxResults, Order[] orders, ICriterion[] criteria) --- End of inner exception stack trace --- ved Castle.ActiveRecord.ActiveRecordBase.SlicedFindAll(Type targetType, Int32 firstResult, Int32 maxResults, Order[] orders, ICriterion[] criteria) ved Castle.ActiveRecord.ActiveRecordBase.FindFirst(Type targetType, Order[] orders, ICriterion[] criteria) ved Castle.ActiveRecord.ActiveRecordBase.FindFirst(Type targetType, ICriterion[] criteria) ved Castle.ActiveRecord.ActiveRecordBase`1.FindFirst(ICriterion[] criteria)

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  • Understanding Javascript's difference between calling a function, and returning the function but executing it later.

    - by Squeegy
    I'm trying to understand the difference between foo.bar() and var fn = foo.bar; fn(); I've put together a little example, but I dont totally understand why the failing ones actually fail. var Dog = function() { this.bark = "Arf"; }; Dog.prototype.woof = function() { $('ul').append('<li>'+ this.bark +'</li>'); }; var dog = new Dog(); // works, obviously dog.woof(); // works (dog.woof)(); // FAILS var fnWoof = dog.woof; fnWoof(); // works setTimeout(function() { dog.woof(); }, 0); // FAILS setTimeout(dog.woof, 0); Which produces: Arf Arf undefined Arf undefined On JSFiddle: http://jsfiddle.net/D6Vdg/1/ So it appears that snapping off a function causes it to remove it's context. Ok. But why then does (dog.woof)(); work? It's all just a bit confusing figuring out whats going on here. There are obviously some core semantics I'm just not getting.

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  • Is there a way communicate or measure levels of abstraction?

    - by hydroparadise
    I'll be the first to say that this question is a bit... out there. But here are a couple questions I bear in mind : Is abstraction continuous or discrete? Is there a single unit of abstraction? But I'm not sure those questions are truly answerable or even really makes sence. My naive answer would be something along the lines of abitrarily discrete but not necescarily having a single unit measure. Here's what I mean... Take a Black Labrador; an abstraction that could be made is that a Black Lab is a type of animal. [Animal]<--[Black Lab] A Black Lab is also a type of Dog. [Dog]<--[Black Lab] One way to establish a degree of abstraction is by comparing the two the abstractions. We could say that [Animal] is more abstract than [Dog] in respect to a Black Lab. It just so happens [Animal] can also be used as an abstraction of [Dog] So, we might end up with something like [Animal]<--[Dog]<--[Black Lab] With the model above, one might be inclined to say that there's two hops of abstraction to get from [Black Lab] to [Animal]. But you can't exactly tell somebody they need one level abstraction and reasonalby expect they will come up with [Dog] given they aren't explicity given the options above. If I needed to tell someobody in a single email that they needed an abstract class with out knowing what that abstract class is, is there a way to communaticate a degree of abstraction such that they might end up on Dog instead of Animal? As a side note, what area of study might this type of analysis fall under?

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  • Extract all related class type aliasing and enum into one file or not

    - by Chen OT
    I have many models in my project, and some other classes just need the class declaration and pointer type aliasing. It does not need to know the class definition, so I don't want to include the model header file. I extract all the model's declaration into one file to let every classes reference one file. model_forward.h class Cat; typedef std::shared_ptr<Cat> CatPointerType; typedef std::shared_ptr<const Cat> CatConstPointerType; class Dog; typedef std::shared_ptr<Dog> DogPointerType; typedef std::shared_ptr<const Dog> DogConstPointerType; class Fish; typedef std::shared_ptr<Fish> FishPointerType; typedef std::shared_ptr<const Fish> FishConstPointerType; enum CatType{RED_CAT, YELLOW_CAT, GREEN_CAT, PURPLE_CAT} enum DogType{HATE_CAT_DOG, HUSKY, GOLDEN_RETRIEVER} enum FishType{SHARK, OCTOPUS, SALMON} Is it acceptable practice? Should I make every unit, which needs a class declaration, depends on one file? Does it cause high coupling? Or I should put these pointer type aliasing and enum definition inside the class back? cat.h class Cat { typedef std::shared_ptr<Cat> PointerType; typedef std::shared_ptr<const Cat> ConstPointerType; enum Type{RED_CAT, YELLOW_CAT, GREEN_CAT, PURPLE_CAT} ... }; dog.h class Dog { typedef std::shared_ptr<Dog> PointerType; typedef std::shared_ptr<const Dog> ConstPointerType; enum Type{HATE_CAT_DOG, HUSKY, GOLDEN_RETRIEVER} ... } fish.h class Fish { ... }; Any suggestion will be helpful.

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  • string combinations

    - by vbNewbie
    I would like to generate a combination of words. For example if I had the following list: {cat, dog, horse, ape, hen, mouse} then the result would be n(n-1)/2 cat dog horse ape hen mouse (cat dog) (dog horse) (horse ape) (ape hen) (hen mouse) (cat dog horse) (dog horse ape) (horse ape hen) etc Hope this makes sense...everything I found involves permutations The list I have would be a 500 long

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  • define a closure as method from class

    - by user272839
    Hi, i'm trying to play with php5.3 and closure. I see here (Listing 7. Closure inside an object : http://www.ibm.com/developerworks/opensource/library/os-php-5.3new2/index.html) that it's possible to use $this in the callback function, but it's not. So I try to give $this as use variable : $self = $this; $foo = function() use($self) { //do something with $self } So to use the same example : class Dog { private $_name; protected $_color; public function __construct($name, $color) { $this->_name = $name; $this->_color = $color; } public function greet($greeting) { $self = $this; return function() use ($greeting, $self) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; }; } } $dog = new Dog("Rover","red"); $dog->greet("Hello"); Output: Hello, I am a red dog named Rover. First of all this example does not print the string but return the function, but that's not my problem. Secondly I can't access to private or protected, because the callback function is a global function and not in the context from the Dog object. Tha't my problem. It's the same as : function greet($greeting, $object) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; } And I want : public function greet($greeting) { echo "$greeting, I am a {$self->_color} dog named {$self->_name}."; } Which is from Dog and not global. I hope that I am clear ...

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  • What is wrong with my version of strchr?

    - by Eduard Saakashvili
    My assignment is to write my own version of strchr, yet it doesn't seem to work. Any advice would be much appreciated. Here it is: char *strchr (const char *s, int c) //we are looking for c on the string s { int dog; //This is the index on the string, initialized as 0 dog = 0; int point; //this is the pointer to the location given by the index point = &s[dog]; while ((s[dog] != c) && (s[dog] != '\0')) { //it keeps adding to dog until it stumbles upon either c or '\0' dog++; } if (s[dog]==c) { return point; //at this point, if this value is equal to c it returns the pointer to that location } else { return NULL; //if not, this means that c is not on the string } }

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  • PHP Passing Data to a Specific Class? (Data Encapsulation)

    - by Adam184
    I've learned that OOP is all about data encapsulation, but what about passing data between classes that have nothing to do with each other (would the below example be worthy of using extends)? class Dog { private $secretVar; public function getSecretVar() { $this->secretVar = 'psst... only for rainbow!'; return $this->secretVar; } } class Rainbow { public function __construct(Dog $Dog) { print_r($Dog->getSecretVar()); } } $Dog = new Dog(); $Rainbow = new Rainbow($Dog); // ... classes that don't need the $secretVar How would you encapsulate $secretVar for only classes Dog and Rainbow? As of now, anyone can call getSecretVar(), and I'm having a hard time allowing that to happen as it seems to defeat the whole point of encapsulation.

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  • Is `List<Dog>` a subclass of `List<Animal>`? Why aren't Java's generics implicitly polymorphic?

    - by froadie
    I'm a bit confused about how Java generics handle inheritance / polymorphism. Assume the following hierarchy - Animal (Parent) Dog - Cat (Children) So suppose I have a method doSomething(List<Animal> animals). By all the rules of inheritance and polymorphism, I would assume that a List<Dog> is a List<Animal> and a List<Cat> is a List<Animal> - and so either one could be passed to this method. Not so. If I want to achieve this behavior, I have to explicitly tell the method to accept a list of any subset of Animal by saying doSomething(List<? extends Animal> animals). I understand that this is Java's behavior. My question is why? Why is polymorphism generally implicit, but when it comes to generics it must be specified?

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  • static block instance block java Order

    - by Rollerball
    Having read this question In what order are the different parts of a class initialized when a class is loaded in the JVM? and the related JLS. I would like to know in more detail why for example having class Animal (superclass) and class Dog (subclass) as following: class Animal { static{ System.out.println("This is Animal's static block speaking"): } { System.out.println("This is Animal's instance block speaking"); } class Dog{ static{ System.out.println("This is Dog's static block speaking"); } { System.out.println("This is Dog's instance block speaking"); } public static void main (String [] args) { Dog dog = new Dog(); } } Ok before instantiating a class its direct superclass needs to be initialized (therefore all the statics variables and block need to be executed). So basically the question is: Why after initializing the static variables and static blocks of the super class, control goes down to the subclass for static variables initialization rather then finishing off the initialization of also the instance member? The control goes like: superclass (Animal): static variables and static blocks subclass (Dog): static variables and static blocks superclass (Animal): instance variables and instance blocks sublcass (Dog):instance variables and instance blocks What is the reason why it is in this way rather than : superclass -> static members superclass -> instance members subclass -> static members sublcass-> instance members

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  • Cast base class object to derived class

    - by Popgalop
    Lets say I have two classes, animal and dog like this. class Animal { }; class Dog : public Animal { }; And I have an animal object named animal, that is actually an instance of dog, how would I cast it back to dog? This may seem like an odd question, but I need it because I am writing a programming language interpreter, and on the stack everything is stored as a BaseObject, and all the other datatypes extend BaseObject. How would I cast the base object from the stack, to a specific data type? I have tried something like this Dog dog = static_cast<Dog>(animal); But it gives me an error 1>------ Build started: Project: StackTests, Configuration: Debug Win32 ------ 1> StackTests.cpp 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2440: 'static_cast' : cannot convert from 'Animal' to 'Dog' 1> No constructor could take the source type, or constructor overload resolution was ambiguous 1>c:\users\owner\documents\visual studio 2012\projects\stacktests\stacktests\stacktests.cpp(173): error C2512: 'Dog' : no appropriate default constructor available ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • Scala factory pattern returns unusable abstract type

    - by GGGforce
    Please let me know how to make the following bit of code work as intended. The problem is that the Scala compiler doesn't understand that my factory is returning a concrete class, so my object can't be used later. Can TypeTags or type parameters help? Or do I need to refactor the code some other way? I'm (obviously) new to Scala. trait Animal trait DomesticatedAnimal extends Animal trait Pet extends DomesticatedAnimal {var name: String = _} class Wolf extends Animal class Cow extends DomesticatedAnimal class Dog extends Pet object Animal { def apply(aType: String) = { aType match { case "wolf" => new Wolf case "cow" => new Cow case "dog" => new Dog } } } def name(a: Pet, name: String) { a.name = name println(a +"'s name is: " + a.name) } val d = Animal("dog") name(d, "fred") The last line of code fails because the compiler thinks d is an Animal, not a Dog.

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