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  • C++ method chaining including class constructor

    - by jena
    Hello, I'm trying to implement method chaining in C++, which turns out to be quite easy if the constructor call of a class is a separate statement, e.g: Foo foo; foo.bar().baz(); But as soon as the constructor call becomes part of the method chain, the compiler complains about expecting ";" in place of "." immediately after the constructor call: Foo foo().bar().baz(); I'm wondering now if this is actually possible in C++. Here is my test class: class Foo { public: Foo() { } Foo& bar() { return *this; } Foo& baz() { return *this; } }; I also found an example for "fluent interfaces" in C++ (http://en.wikipedia.org/wiki/Fluent_interface#C.2B.2B) which seems to be exactly what I'm searching for. However, I get the same compiler error for that code. Thanks in advance for any hint. Best, Jean

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  • Method overloading in groovy

    - by slojo
    I am trying to take advantage of the convenience of groovy's scripting syntax to assign properties, but having trouble with a specific case. I must be missing something simple here. I define class A, B, C as so: class A { A() { println "Constructed class A!" } } class B { B() { println "Constructed class B!" } } class C { private member C() { println "Constructed class C!" } def setMember(A a) { println "Called setMember(A)!" member = a } def setMember(B b) { println "Called setMember(B)!" member = b } } And then try the following calls in a script: c = new C() c.setMember(new A()) // works c.member = new A() // works c.setMember(new B()) // works c.member = new B() // doesn't work! The last assignment results in an error: 'Cannot cast object of class B to class A". Why doesn't it call the proper setMember method for class B like it does for class A?

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  • Calling overridden parent method from parent method

    - by Yisroel
    Heres the situation. Component B extends component A and overrides the init method to accept a different parameter. A also has a create method that calls init. If i have an instance of B and i call create, its calling the wrong init - it calls init in B, where i need it to call init in A. I dont want to call super.init() as there may not always be a super. Is there any way to specify to call the init in the parent component?

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  • Java method keyword "final" and its use

    - by Lukas Eder
    When I create complex type hierarchies (several levels, several types per level), I like to use the final keyword on methods implementing some interface declaration. An example: interface Garble { int zork(); } interface Gnarf extends Garble { /** * This is the same as calling {@link #zblah(0)} */ int zblah(); int zblah(int defaultZblah); } And then abstract class AbstractGarble implements Garble { @Override public final int zork() { ... } } abstract class AbstractGnarf extends AbstractGarble implements Gnarf { // Here I absolutely want to fix the default behaviour of zblah // No Gnarf shouldn't be allowed to set 1 as the default, for instance @Override public final int zblah() { return zblah(0); } // This method is not implemented here, but in a subclass @Override public abstract int zblah(int defaultZblah); } I do this for several reasons: It helps me develop the type hierarchy. When I add a class to the hierarchy, it is very clear, what methods I have to implement, and what methods I may not override (in case I forgot the details about the hierarchy) I think overriding concrete stuff is bad according to design principles and patterns, such as the template method pattern. I don't want other developers or my users do it. So the final keyword works perfectly for me. My question is: Why is it used so rarely in the wild? Can you show me some examples / reasons where final (in a similar case to mine) would be very bad?

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  • Does C# allow method overloading, PHP style (__call)?

    - by mr.b
    In PHP, there is a special method named __call($calledMethodName, $arguments), which allows class to catch calls to non-existing methods, and do something about it. Since most of classic languages are strongly typed, compiler won't allow calling a method that does not exist, I'm clear with that part. What I want to accomplish (and I figured this is how I would do it in PHP, but C# is something else) is to proxy calls to a class methods and log each of these calls. Right now, I have code similar to this: class ProxyClass { static logger; public AnotherClass inner { get; private set; } public ProxyClass() { inner = new AnotherClass(); } } class AnotherClass { public void A() {} public void B() {} public void C() {} // ... } // meanwhile, in happyCodeLandia... ProxyClass pc = new ProxyClass(); pc.inner.A(); pc.inner.B(); // ... So, how can I proxy calls to an object instance in extensible way? Extensible, meaning that I don't have to modify ProxyClass whenever AnotherClass changes. In my case, AnotherClass can have any number of methods, so it wouldn't be appropriate to overload or wrap all methods to add logging. I am aware that this might not be the best approach for this kind of problem, so if anyone has idea what approach to use, shoot. Thanks!

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  • Django: Overriding the save() method: how do I call the delete() method of a child class

    - by Patti
    The setup = I have this class, Transcript: class Transcript(models.Model): body = models.TextField('Body') doPagination = models.BooleanField('Paginate') numPages = models.PositiveIntegerField('Number of Pages') and this class, TranscriptPages(models.Model): class TranscriptPages(models.Model): transcript = models.ForeignKey(Transcript) order = models.PositiveIntegerField('Order') content = models.TextField('Page Content', null=True, blank=True) The Admin behavior I’m trying to create is to let a user populate Transcript.body with the entire contents of a long document and, if they set Transcript.doPagination = True and save the Transcript admin, I will automatically split the body into n Transcript pages. In the admin, TranscriptPages is a StackedInline of the Transcript Admin. To do this I’m overridding Transcript’s save method: def save(self): if self.doPagination: #do stuff super(Transcript, self).save() else: super(Transcript, self).save() The problem = When Transcript.doPagination is True, I want to manually delete all of the TranscriptPages that reference this Transcript so I can then create them again from scratch. So, I thought this would work: #do stuff TranscriptPages.objects.filter(transcript__id=self.id).delete() super(Transcript, self).save() but when I try I get this error: Exception Type: ValidationError Exception Value: [u'Select a valid choice. That choice is not one of the available choices.'] ... and this is the last thing in the stack trace before the exception is raised: .../django/forms/models.py in save_existing_objects pk_value = form.fields[pk_name].clean(raw_pk_value) Other attempts to fix: t = self.transcriptpages_set.all().delete() (where self = Transcript from the save() method) looping over t (above) and deleting each item individually making a post_save signal on TranscriptPages that calls the delete method Any ideas? How does the Admin do it? UPDATE: Every once in a while as I'm playing around with the code I can get a different error (below), but then it just goes away and I can't replicate it again... until the next random time. Exception Type: MultiValueDictKeyError Exception Value: "Key 'transcriptpages_set-0-id' not found in " Exception Location: .../django/utils/datastructures.py in getitem, line 203 and the last lines from the trace: .../django/forms/models.py in _construct_form form = super(BaseInlineFormSet, self)._construct_form(i, **kwargs) .../django/utils/datastructures.py in getitem pk = self.data[pk_key]

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  • How to find the first declaring method for a reference method

    - by Oliver Gierke
    Suppose you have a generic interface and an implementation: public interface MyInterface<T> { void foo(T param); } public class MyImplementation<T> implements MyInterface<T> { void foo(T param) { } } These two types are frework types. In the next step I want allow users to extend that interface as well as redeclare foo(T param) to maybe equip it with further annotations. public interface MyExtendedInterface extends MyInterface<Bar> { @Override void foo(Bar param); // Further declared methods } I create an AOP proxy for the extended interface and intercept especially the calls to furtherly declared methods. As foo(…) is no redeclared in MyExtendedInterface I cannot execute it by simply invoking MethodInvocation.proceed() as the instance of MyImplementation only implements MyInterface.foo(…) and not MyExtendedInterface.foo(…). So is there a way to get access to the method that declared a method initially? Regarding this example is there a way to find out that foo(Bar param) was declared in MyInterface originally and get access to the accoriding Method instance? I already tried to scan base class methods to match by name and parameter types but that doesn't work out as generics pop in and MyImplementation.getMethod("foo", Bar.class) obviously throws a NoSuchMethodException. I already know that MyExtendedInterface types MyInterface to Bar. So If I could create some kind of "typed view" on MyImplementation my math algorithm could work out actually.

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  • Encapsulate update method inside of object or have method which accepts an object to update

    - by Tom
    Hi, I actually have 2 questions related to each other: I have an object (class) called, say MyClass which holds data from my database. Currently I have a list of these objects ( List < MyClass ) that resides in a singleton in a "communal area". I feel it's easier to manage the data this way and I fail to see how passing a class around from object to object is beneficial over a singleton (I would be happy if someone can tell me why). Anyway, the data may change in the database from outside my program and so I have to update the data every so often. To update the list of the MyClass I have a method called say, Update, written in another class which accepts a list of MyClass. This updates all the instances of MyClass in the list. However would it be better instead to encapulate the Update() method inside the MyClass object, so instead I would say foreach(MyClass obj in MyClassList) { obj.update(); } What is a better implementation and why? The update method requires a XML reader. I have written an XML reader class which is basically a wrapper over the standard XML reader the language natively provides which provides application specific data collection. Should the XML reader class be in anyway in the "inheritance path" of the MyClass object - the MyClass objects inherits from the XML reader because it uses a few methods. I can't see why it should. I don't like the idea of declaring an instance of the XML Reader class inside of MyClass and an MyClass object is meant to be a simple "record" from the database and I feel giving it loads of methods, other object instances is a bit messy. Perhaps my XML reader class should be static but C#'s native XMLReader isn't static.? Any comments would be greatly appreciated Thanks Thomas

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  • Calling a class method within a method definition in the same class

    - by user1786288
    So I'm writing a program for an intro Java class. I'm defining a method to add two fractions together within the class Fraction. Fraction has 2 variables, numerator and denominator. Each of these variables has a setter and a getter. Anyway, I have a problem with my addition method, which is shown below. I've just sort of tried to implement it in a way that made sense, but I'm sure I did something with calling methods/using objects that doesn't work. public void add(Fraction fraction1, Fraction fraction2) { Fraction fraction3 = new Fraction(); int a = fraction1.getNumerator; int b = fraction1.getDenominator; int c = fraction2.getNumerator; int d = fraction2.getDenominator; fraction3.setNumerator((a * d) + (b * c)); fraction3.setDenominator(b * d); } I don't know if the problem is in the method definition, if I can use the object type that way, or if there's something else wrong. any help would be appreciated, and if I need to provide any information, I'll do so ASAP.

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  • Overwrite HTTP method with JAX-RS

    - by deamon
    Today's browsers (or HTML < 5) only support HTTP GET and POST, but to communicate RESTful one need PUT and DELETE too. If the workaround should not be to use Ajax, something like a hidden form field is required to overwrite the actual HTTP method. Rails uses the following trick: <input name="_method" type="hidden" value="put" /> Is there a possibility to do something similar with JAX-RS?

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  • Is factory method proper design for my problem?

    - by metdos
    Hello Everyone, here is my problem and I'm considering to use factory method in C++, what are your opinions ? There are a Base Class and a lot of Subclasses. I need to transfer objects on network via TCP. I will create objects in first side, and using this object I will create a byte array TCP message, and send it to other side. On the other side I will decompose TCP message, I will create object and I will add this object to a polymorphic queue.

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  • What is wrong with this c# method?

    - by bala3569
    I use this method to get file extension, public string ReturnExtension(string fileExtension) { switch (fileExtension) { case ".doc": case ".docx": return "application/ms-word"; } } When i compile it i got the error BaseClass.ReturnExtension(string)': not all code paths return a value.. Any suggestion...

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  • Using the masters method

    - by Roarke
    On my midterm I had the problem: t(n) = 8T(n/2) +n^3 and I am supposed to find its big theta notation using either the masters or alternative method. So what i did was a = 8, b = 2 k = 3 log8 (base 2) = 3 = k therefore, T(n) is big theta n^3. I got 1/3 points so i must be wrong. What did I do wrong?

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  • get request.session from a model method in django

    - by dotty
    Hay, is it possible to a get a request.session value from a model method in django? Here is what i need def html(self): Template = loader.get_template("inclusions/Template") return Template.render(Context({ 'user_id':request.session['user'].id })) user_id would be request.session['user'].id

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  • Why do all procedures have to be defined before the compiler sees them?

    - by incrediman
    For example, take a look at this code (from tspl4): (define proc1 (lambda (x y) (proc2 y x))) If I run this as my program in scheme... #!r6rs (import (rnrs)) (define proc1 (lambda (x y) (proc2 y x))) I get this error: expand: unbound identifier in module in: proc2 ...This code works fine though: #!r6rs (import (rnrs)) (define proc2 +) (define proc1 (lambda (x y) (proc2 y x))) (display (proc1 2 3)) ;output: 5

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  • Calling javascript method from from inside object

    - by John
    I am struggling with methods in JavaScript. obj = function(){ this.getMail = function getMail (){ } //Here I would like to run the get mail once but this.getMail() or getMail() wont work } var mail = new obj(); mail.getMail(); How do I make the method in a way that I can run it both inside the object and from the outside Thanks

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  • Can I use #undef this way?

    - by flyout
    I want to get some settings I store in the registry, and if they differ from a #define I want to redefine it, could I do it this way?: #define DEFINED_X "testSetting" void LoadConfig() { regConfigX = some value previusly stored in the registry; if(regConfigX!=DEFINED_X) { #undef DEFINED_X #define DEFINED_X regConfigX } } I tought #define was used only when compiling, would this code work when running the compiled exe?

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  • Checking method visibility in PHP

    - by phobia
    Is there any way of checking if a class method has been declared as private or public? I'm working on a controller where the url is mapped to methods in the class, and I only want to trigger the methods if they are defined as public.

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  • ocjective-c Obtain return value from public method

    - by Felix
    I'm pretty new to objective-C (and C in general) and iPhone development and am coming from the java island, so there are some fundamentals that are quite tough to learn for me. I'm diving right into iOS5 and want to use storyboards. For now I am trying to setup a list in a UITableViewController that will be filled with values returned by a web service in the future. For now, I just want to generate some mock objects and show their names in the list to be able to proceed. Coming from java, my first approach would be to create a new Class that provides a global accessible method to generate some objects for my list: #import <Foundation/Foundation.h> @interface MockObjectGenerator : NSObject +(NSMutableArray *) createAndGetMockProjects; @end Implementation is... #import "MockObjectGenerator.h" // Custom object with some fields #import "Project.h" @implementation MockObjectGenerator + (NSMutableArray *) createAndGetMockObjects { NSMutableArray *mockProjects = [NSMutableArray alloc]; Project *project1 = [Project alloc]; Project *project2 = [Project alloc]; Project *project3 = [Project alloc]; project1.name = @"Project 1"; project2.name = @"Project 2"; project3.name = @"Project 3"; [mockProjects addObject:project1]; [mockProjects addObject:project2]; [mockProjects addObject:project3]; } And here is my ProjectTable.h that is supposed to control my ListView #import <UIKit/UIKit.h> @interface ProjectsTable : UITableViewController @property (strong, nonatomic) NSMutableArray *projectsList; @end And finally ProjectTable.m #import "ProjectsTable.h" #import "Project.h" #import "MockObjectGenerator.h" @interface ProjectsTable { @synthesize projectsList = _projectsList; -(id)initWithStyle:(UITableViewStyle:style { self = [super initWithStyle:style]; if (self) { _projectsList = [[MockObjectGenerator createAndGetMockObjects] copy]; } return self; } - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { // only one section for all return 1; - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { NSLog(@"%d entries in list", _projectsList.count); return _projectsList.count; - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { // the identifier of the lists prototype cell is set to this string value static NSString *CellIdentifier = @"projectCell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; Project *project = [_projectsList objectAtIndex:indexPath.row]; cell.textLabel.text = project.name } So while I think everything is correctly set, I expect the tableView to show my three mock objects in its rows. But it stays empty and the NSLog method prints "0 entries in list" into the console. So what am I doing wrong? Any help is appreciated. Best regards Felix

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  • method implementation for this case in Java

    - by Thomas
    Hello, I just saw a code snippet like this: private static class DefaultErrorHandler<RT> implements ErrorHandler<RT> { public RT handle(Object[] params, Throwable e) { return Exceptions.throwUncheckedException(e); } Now I am wondering what the static method "throwUncheckedException (Throwable e)" would return exactly and how it might be implemented regarding the generics. Can anybody give me an example ?

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  • When is a parameterized method call useful?

    - by johann-christoph-jacob
    A Java method call may be parameterized like in the following code: class Test { <T> void test() { } public static void main(String[] args) { new Test().<Object>test(); // ^^^^^^^^ } } I found out this is possible from the Eclipse Java Formatter settings dialog and wondered if there are any cases where this is useful or required.

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  • How to use method hiding (new) with generic constrained class

    - by ongle
    I have a container class that has a generic parameter which is constrained to some base class. The type supplied to the generic is a sub of the base class constraint. The sub class uses method hiding (new) to change the behavior of a method from the base class (no, I can't make it virtual as it is not my code). My problem is that the 'new' methods do not get called, the compiler seems to consider the supplied type to be the base class, not the sub, as if I had upcast it to the base. Clearly I am misunderstanding something fundamental here. I thought that the generic where T: xxx was a constraint, not an upcast type. This sample code basically demonstrates what I'm talking about. using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace GenericPartialTest { class ContextBase { public string GetValue() { return "I am Context Base: " + this.GetType().Name; } public string GetOtherValue() { return "I am Context Base: " + this.GetType().Name; } } partial class ContextSub : ContextBase { public new string GetValue() { return "I am Context Sub: " + this.GetType().Name; } } partial class ContextSub { public new string GetOtherValue() { return "I am Context Sub: " + this.GetType().Name; } } class Container<T> where T: ContextBase, new() { private T _context = new T(); public string GetValue() { return this._context.GetValue(); } public string GetOtherValue() { return this._context.GetOtherValue(); } } class Program { static void Main(string[] args) { Console.WriteLine("Simple"); ContextBase myBase = new ContextBase(); ContextSub mySub = new ContextSub(); Console.WriteLine(myBase.GetValue()); Console.WriteLine(myBase.GetOtherValue()); Console.WriteLine(mySub.GetValue()); Console.WriteLine(mySub.GetOtherValue()); Console.WriteLine("Generic Container"); Container<ContextBase> myContainerBase = new Container<ContextBase>(); Container<ContextSub> myContainerSub = new Container<ContextSub>(); Console.WriteLine(myContainerBase.GetValue()); Console.WriteLine(myContainerBase.GetOtherValue()); Console.WriteLine(myContainerSub.GetValue()); Console.WriteLine(myContainerSub.GetOtherValue()); Console.ReadKey(); } } }

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