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• Question about member function pointers in a heirarchy

  - by Jesse Beder

  I'm using a library that defines an interface: template<class desttype> void connect(desttype* pclass, void (desttype::*pmemfun)()); and I have a small heirarchy class base { void foo(); }; class derived: public base { ... }; In a member function of derived, I want to call connect(this, &derived::foo); but it seems that &derived::foo is actually a member function pointer of base; gcc spits out error: no matching function for call to ‘connect(derived* const&, void (base::* const&)())’ I can get around this by explicitly casting this to base *; but why can't the compiler match the call with desttype = base (since derived * can be implicitly cast to base *)? Also, why is &derived::foo not a member function pointer of derived?

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• How to use reflection to get a default constructor?

  - by Qwertie

  I am writing a library that generates derived classes of abstract classes dynamically at runtime. The constructor of the derived class needs a MethodInfo of the base class constructor so that it can invoke it. However, for some reason Type.GetConstructor() returns null. For example: abstract class Test { public abstract void F(); } public static void Main(string[] args) { ConstructorInfo constructor = typeof(Test).GetConstructor( BindingFlags.NonPublic | BindingFlags.Public, null, System.Type.EmptyTypes, null); // returns null! } Note that GetConstructor returns null even if I explicitly declare a constructor in Test, and even if Test is not abstract.

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• Implements an Undo/Redo in MVC

  - by bnabilos

  Hello, I have a Java application and I want to implement an Undo/Redo option. the value that I want to stock and that I want to be able to recover is an integer. My Class Model implements the interface StateEditable and I have to redefine the 2 functions restoreState(Hashtable<?, ?> state) and storeState(Hashtable<Object, Object> state) but I don't know what to put on them. It will be really great if somebody can help me to do that. These are the first lines of my Model class, the value that I want to do an undo/redo on it is value public class Model extends Observable implements StateEditable { private int value = 5; private UndoManager undoRedo = new UndoManager(); final UndoableEditListener editListener = new UndoableEditListener() { public void undoableEditHappened(UndoableEditEvent evt) { undoRedo.addEdit(evt.getEdit()); } }; @Override public void restoreState(Hashtable<?, ?> state) { } @Override public void storeState(Hashtable<Object, Object> state) { } }

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• Problem deploying GWT application on apache and tomcat using mod_jk

  - by Colin

  I'm trying to deploy a GWT app on Apache using mod_jk connector. I have compiled the application and tested it on tomcat on the address localhost:8080/loginapp and it works ok. However when I deploy it to apache using mod_jk I get the starter page which gives me a login form but trying to login I get this error 404 Not Found Not Found The requested URL /loginapp/loginapp/login was not found on this server Looking at the apache log files i see this [Thu Jan 13 13:43:17 2011] [error] [client 127.0.0.1] client denied by server configuration: /usr/local/tomcat/webapps/loginapp/WEB-INF/ [Thu Jan 13 13:43:26 2011] [error] [client 127.0.0.1] File does not exist: /usr/local/tomcat/webapps/loginapp/loginapp/login, referer: http://localhost/loginapp/LoginApp.html The mod_jk configurations on my apache2.conf file are as follows LoadModule jk_module /usr/lib/apache2/modules/mod_jk.so JkWorkersFile /etc/apache2/workers.properties JkLogFile /var/log/apache2/mod_jk.log JkLogLevel info JkLogStampFormat "[%a %b %d %H:%M:%S %Y] " JkOptions +ForwardKeySize +ForwardURICompat -ForwardDirectories JkRequestLogFormat "%w %V %T" <IfModule mod_jk.c> Alias /loginapp "/usr/local/tomcat/webapps/loginapp/" <Directory "/usr/local/tomcat/webapps/loginapp/"> Options Indexes +FollowSymLinks AllowOverride None Allow from all </Directory> <Location /*/WEB-INF/*> AllowOverride None deny from all </Location> JkMount /loginapp/*.html loginapp My workers.properties file is as follows workers.tomcat_home=/usr/local/tomcat workers.java_home=/usr/lib/jvm/java-6-sun ps=/ worker.list=loginapp worker.loginapp.type=ajp13 worker.loginapp.host=localhost worker.loginapp.port=8009 worker.loginapp.cachesize=10 worker.loginapp.cache_timeout=600 worker.loginapp.socket_keepalive=1 worker.loginapp.recycle_timeout=300 worker.loginapp.lbfactor=1 And this is my servlet mappings for my app on the application's web.xml <servlet> <servlet-name>loginServlet</servlet-name> <servlet-class>com.example.loginapp.server.LoginServiceImpl</servlet-class> </servlet> <servlet-mapping> <servlet-name>loginServlet</servlet-name> <url-pattern>/loginapp/login</url-pattern> </servlet-mapping> <servlet> <servlet-name>myAppServlet</servlet-name> <servlet-class>com.example.loginapp.server.MyAppServiceImpl</servlet-class> </servlet> <servlet-mapping> <servlet-name>myAppServlet</servlet-name> <url-pattern>/loginapp/mapdata</url-pattern> </servlet-mapping> Ive tried everything and it seems to still elude me. Even tried changing the deny from all directive on the WEBINF folder to allow from all and still it doesnt work. Maybe im missing something. Any help will be highly appreciated.

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• How to inject dependencies into a custom UserNamePasswordValidator in WCF?

  - by Dannerbo

  I'm using a UserNamePasswordValidator in WCF along with Unity for my dependency injection, but since WCF creates the instance of the UserNamePasswordValidator, I cannot inject my container into the class. So how would one go about this? The simplest solution I can think of is to create a static proxy/wrapper class around a static instance of a UnityContainer, which exposes all the same methods... This way, any class can access the container, and I don't need to inject it everywhere. So I could just do UnityContainerWrapper.Resolve() anywhere in code. So basically this solution solves 2 problems for me, I can use it in classes that I'm not creating an instance of, and I can use it anywhere without having to inject the container into a bunch of classes. The only downside I can think of is that I'm now potentially exposing my container to a bunch of classes that wouldn't of had access to the container before. Not really sure if this is even a problem though?

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• MVC3 Razor DropDownListFor Enums

  - by jordan.baucke

  Trying to get my project updated to MVC3, something I just can't find: I have a simple datatype of ENUMS: public enum States() { AL,AK,AZ,...WY } Which I want to use as a DropDown/SelectList in my view of a model that contains this datatype: public class FormModel() { public States State {get; set;} } Pretty straight forward: when I go to use the auto-generate view for this partial class, it ignores this type. I need a simple select list that sets the value of the enum as the selected item when I hit submit and process via my AJAX - JSON POST Method. And than the view (???!): <div class="editor-field"> @Html.DropDownListFor(model => model.State, model => model.States) </div> thanks in advance for the advice!

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• Equivalent of public static final fields in Scala

  - by JT

  I'm learning Scala, and I can't figure out how to best express this simple Java class in Scala: public class Color { public static final Color BLACK = new Color(0, 0, 0); public static final Color WHITE = new Color(255, 255, 255); public static final Color GREEN = new Color(0, 0, 255); private static final int red; private static final int blue; private static final int green; public Color(int red, int blue, int green) { this.red = red; this.blue = blue; this.green = green; } // getters, et cetera } The best I have is the following: class Color(val red: Int, val blue: Int, val green: Int) object BLACK extends Color(0, 0, 0) object WHITE extends Color(255, 255, 255) object GREEN extends Color(0, 0, 255) But I lose the advantages of having BLACK, WHITE, and GREEN being tied to the Color namespace.

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• has_many through a habtm relationship in Rails

  - by macek

  I'm trying to define a has_many X, :through => Y where Y is a habtm relationship. Rails is throwing a fit about this. See comment in user model: class User < ActiveRecord::Base has_many :posts # I want to display a list of all tags this user is involved in has_many :tags, :through => :posts # ERROR end class Post < ActiveRecord::Base has_and_belongs_to_many :tags end class Tag < ActiveRecord::Base has_and_belongs_to_many :posts end What can I do to fix this?

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• Good programming style when handling multiple objects

  - by Glitch

  I've been programming a software version of a board game. Thus far I have written the classes which will correspond to physical objects on the game board. I'm well into writing the program logic, however I've found that many of the logic classes require access to the same objects. At first I was passing the appropriate objects to methods as they were called, but this was getting very tedious, particularly when the methods required many objects to perform their tasks. To solve this, I created a class which initialises and stores all the objects I need. This allows me to access an object from any class by calling Assets.dice(), for example. But now that I've thought about it, this doesn't seem right. This is why I'm here, I fear that I've created some sort of god class. Is this fear unfounded, or have I created a recipe for disaster?

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• Using Interfaces in JNI

  - by lhw

  I am trying to use (*env)->RegisterNatives to add methods to a defined class which I then add to a callback list. The callback sender of course expects my class to implement a certain interface which I do not. And is failing on execution. If I add the keyword "implements Listener" to my class in Java the javac expects to have the methods definition in Java or with native keyword which I try to avoid here, as I'd like to register the methods within the JNI_OnLoad and execute one of them afterwards. The question now is: Can I implement the interface in JNI or avoid the error message in Java?

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• Assign fixed IP address via DHCP by DNS lookup

  - by Janoszen

  Preface I'm building a virtualization environment with Ubuntu 14.04 and LXC. I don't want to write my own template since the upgrade from 12.04 to 14.04 has shown that backwards compatibility is not guaranteed. Therefore I'm deploying my virtual machines via lxc-create, using the default Ubuntu template. The DNS for the servers is provided by Amazon Route 53, so no local DNS server is needed. I also use Puppet to configure my servers, so I want to keep the manual effort on the deployment minimal. Now, the default Ubuntu template assigns IP addresses via DHCP. Therefore, I need a local DHCP server to assign IP addresses to the nodes, so I can SSH into them and get Puppet running. Since Puppet requires a proper DNS setup, assigning temporary IP addresses is not an option, the client needs to get the right hostname and IP address from the start. Question What DHCP server do I use and how do I get it to assign the IP address based only on the host-name DHCP option by performing a DNS lookup on that very host name? What I've tried I tried to make it work using the ISC DHCP server, however, the manual clearly states: Please be aware that only the dhcp-client-identifier option and the hardware address can be used to match a host declaration, or the host-identifier option parameter for DHCPv6 servers. For example, it is not possible to match a host declaration to a host-name option. This is because the host-name option cannot be guaranteed to be unique for any given client, whereas both the hardware address and dhcp-client-identifier option are at least theoretically guaranteed to be unique to a given client. I also tried to create a class that matches the hostname like this: class "my-client-name" { match if option host-name = "my-client-name"; fixed-address my-client-name.my-domain.com; } Unfortunately the fixed-address option is not allowed in class statements. I can replace it with a 1-size pool, which works as expected: subnet 10.103.0.0 netmask 255.255.0.0 { option routers 10.103.1.1; class "my-client-name" { match if option host-name = "my-client-name"; } pool { allow members of "my-client-name"; range 10.103.1.2 10.103.1.2; } } However, this would require me to administer the IP addresses in two places (Amazon Route53 and the DHCP server), which I would prefer not to do. About security Since this is only used in the bootstrapping phase on an internal network and is then replaced by a static network configuration by Puppet, this shouldn't be an issue from a security standpoint. I am, however, aware that the virtual machine bootstraps with "ubuntu:ubuntu" credentials, which I intend to fix once this is running.

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• Use the [Serializable] attribute or subclassing from MarshalByRefObject?

  - by Theo Lenndorff

  I'd like to use an object across AppDomains. For this I can use the [Serializeable] attribute: [Serializable] class MyClass { public string GetSomeString() { return "someString" } } Or subclass from MarshalByRefObject: class MyClass: MarshalByRefObject { public string GetSomeString() { return "someString" } } In both cases I can use the class like this: AppDomain appDomain = AppDomain.CreateDomain("AppDomain"); MyClass myObject = (MyClass)appDomain.CreateInstanceAndUnwrap( typeof(MyClass).Assembly.FullName, typeof(MyClass).FullName); Console.WriteLine(myObject.GetSomeString()); Why do both approaches seem to have the same effect? What is the difference in both approaches? When should I favor the one approach over the other? EDIT: At the surface I know that there are differences between both mechanisms, but if someone jumped out of a bush and asked me the question I couldn't give him a proper answer. The questions are quite open questions. I hoped that someone can explain it better than I could do.

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• How do I get the XAML comiler to use textual content property on custom classes?

  - by Duncan

  Given a simple C# class definition like: [System.Windows.Markup.ContentProperty("PropertyOne")] public class SimpleBase { public string PropertyOne { get; set; } public string PropertyTwo { get; set; } } why is it not possible to ommit the sys:string tags around the word Test in the xaml below. <custom:SimpleBase x:Class="TestType" xmlns:custom="clr-namespace:ConsoleApplication1;assembly=" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:sys="clr-namespace:System;assembly=mscorlib"> <sys:String>Test</sys:String> </custom:SimpleBase> Somehow the compiler correctly coverts text to string for the type String, why doesn't it work for my custom type? The context can be found on my blog: http://www.deconflations.com/?tag=xaml

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• Types in Python - Google Appengine

  - by Chris M

  Getting a bit peeved now; I have a model and a class thats just storing a get request in the database; basic tracking. class SearchRec(db.Model): WebSite = db.StringProperty()#required=True WebPage = db.StringProperty() CountryNM = db.StringProperty() PrefMailing = db.BooleanProperty() DateStamp = db.DateTimeProperty(auto_now_add=True) IP = db.StringProperty() class AddSearch(webapp.RequestHandler): def get(self): searchRec = SearchRec() searchRec.WebSite = self.request.get('WEBSITE') searchRec.WebPage = self.request.get('WEBPAGE') searchRec.CountryNM = self.request.get('COUNTRY') searchRec.PrefMailing = bool(self.request.get('MAIL')) searchRec.IP = self.request.get('IP') Bool has my biscuit; I thought that setting bool(self.reque....) would set the type of the string but no matter what I pass it it still stores it as TRUE in the database. I had the same issue with using required=True on strings for the model; the damn thing kept saying that nothing was being passed... but it had. Ta

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• Type casting in TPC inheritance

  - by Mohsen Esmailpour

  I have several products like HotelProduct, FlightProduct ... which derived from BaseProduct class. The table of these products will be generated in TPC manner in database. There is OrderLine class which has a BaseProduct. My problem is when i select an OrderLine with related product i don't know how cast BaseProduct to derived product. for example i have this query: var order = (from odr in _context.Orders join orderLine in _context.OrderLines on odr.Id equals orderLine.OrderId join hotel in _context.Products.OfType<HotelProduct>() on orderLine.ProductId equals hotel.Id where odr.UserId == userId && odr.Id == orderId orderby odr.OrderDate descending select odr).SingleOrDefault(); In OrderLine i have BaseProduct properties not properties of HotelProduct. Is there any way to cast BaseProduct to derived class in OrderLine or any other solutions ?

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• how can I implement Comparable more than once?

  - by codeman73

  I'm upgrading some code to Java 5 and am clearly not understanding something with Generics. I have other classes which implement Comparable once, which I've been able to implement. But now I've got a class which, due to inheritance, ends up trying to implement Comparable for 2 types. Here's my situation: I've got the following classes/interfaces: interface Foo extends Comparable<Foo> interface Bar extends Comparable<Bar> abstract class BarDescription implements Bar class FooBar extends BarDescription implements Foo With this, I get the error 'interface Comparable cannot be implemented more than once with different arguments...' Why can't I have a compareTo(Foo foo) implemented in FooBar, and also a compareTo(Bar) implemented in BarDescription? Isn't this simply method overloading?

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• Display value of a django form field in a template?

  - by Eran Kampf

  I have a form with an email property. When using {{ form.email }} in case of some validation error, django still renders the previous value in the input tag's value attribute: <input type="text" id="id_email" maxlength="75" class="required" value="[email protected]" name="email"> I want to render the input tag myself (to add some javascript code and an error class in case of an error). For example this is my template instead of {{ form.email }}: <input type="text" autocomplete="on" id="id_email" name="email" class="email {% if form.email.errors %}error{% endif %}"> However this does not display the errorneous value ("[email protected]" in this example) to the user. How do I get the field's value in the template?

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• Why is the base() constructor not necessary?

  - by Earlz

  Hello, I have a class structure like abstract class Animal { public Animal(){ //init stuff.. } } class Cat : Animal { public Cat(bool is_keyboard) : base() //NOTE here { //other init stuff } } Now then, look at the noted line. If you remove : base() then it will compile without an error. Why is this? Is there a way to disable this behavior? I have had multiple bugs now from forgetting the base() which I would have thought to be required on such a special thing as a constructor.

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• running a program in Unix vs in Windows

  - by Hristo

  I'm compiling a simple program written in C and I'm using Eclipse as an IDE, both in Windows 7 and on my MacBook Pro. Very simple program my friend wrote and asked me to help him with: int a = 0; char b[2]; printf("Input first class info:\n"); printf("Credit Hours: \n"); scanf("%d", &a); printf("Letter Grade: "); scanf("%s", b); So when I run this on my mac, each line prints and when I encounter the scanf(), I can input and continue as expected. In Windows, I have to input everything and then it will print all the lines. I'm not sure why this is happening... what is the difference b/w Windows and Mac here? Mac: Input first class info: Credit Hours: 4 Letter Grade: B+ Windows: 4 B+ Input first class info: Credit Hours: Letter Grade: Thanks, Hristo

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• What's the reason both Image and Bitmap classes don't implement a custom equality/hashcode logic?

  - by devoured elysium

  From MSDN documentation, it seems as both GetHashCode() and Equals() haven't been overriden in Bitmap. Neither have them been overriden in Image. So both classes are using the Object's version of them just compares references. I wasn't too convinced so I decided to fire up Reflector to check it out. It seems MSDN is correct in that matter. So, is there any special reason why MS guys wouldn't implement "comparison logic", at least for the Bitmap class? I find it is kinda acceptable for Image, as it is an abstract class, but not so much for the Bitmap class. I can see in a lot of situations calculating the hash code can be an expensive operation, but it'd be alright if it used some kind of lazy evaluation (storing the computed hash code integer in a variable a variable, so it wouldn't have to calculate it later again). When wanting to compare 2 bitmaps, will I have to resort to having to run all over the picture comparing each one of its pixels? Thanks

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• How to override the behavior of Spring @Autowired

  - by Mark

  Hi a little background: I am Using Spring 2.5, and specifically spring IOC and annotations. I am using @Autowired in my code (the Autowiring is done by type) and use @Component for exposing Classes to the Automatic wiring. The situation described bellow arose while i tried to test my code. now to the problem: Note: i use a different Spring Context for the Test environment. I have a class FOO which is @Autowired but in the test context i want to use a different class of the same type MockFoo (extends FOO) The Spring Setup of course fails do so automatically due to multiple options for the Dependency Injection of the FOO class (both FOO and MockFOO comply to the Type check) I am looking for a way to inject the test bean instead of the original bean. I expected Spring to allow using the Context configurion file to override a bean injection or to order Spring not to autowire a specific bean BUT All these option seem to exists only for the beans which were originally defined in the Spring Context Configuration file

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• BLL returning the right Type of an instance

  - by Younes

  I have a class "Artikel" and there i write some Business Logic. I also have a class "tArtikel" which is a type. In my class "Artikel" I work with "tArtikel" and returns are of that type. Now when i instantiate an "Artikel" i want it to be of type "tArtikel", so what i tried in my code is: public tArtikel Artikel() { tArtikel artikel = new tArtikel(); } Which results in: "'Artikel' member names cannot be the same as their enclosing type". How would i set this up correctly?

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• belongs_to with a custom class_name not producing proper foreign key in Rails 3

  - by Tony

  I am updating an application to Rails 3 and I am having trouble creating a custom foreign key. I have something like this: class Product < ActiveRecord::Base belongs_to :owner, :class_name => 'User' ... end class User < ActiveRecord::Base has_many :products ... end class ProductsController < ApplicationController before_filter :authenticate_user! def index @products = current_user.products end end The view: <%- @products.each do |p| -%> <%= p.created_at %><br /> <%- end -%> I get this error in my Rails log: Mysql::Error: Unknown column 'products.user_id' in 'where clause': SELECT `products`.* FROM `products` WHERE (`products`.user_id = 1) It should see the belongs_to :owner and look for a foreign key called owner_id. I even tried explicitly setting the foreign key and that does not work. I also checked lighthouse for a possible Rails 3 bug but no luck.

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• What's the Best Way to Navigate Silverlight XAML in Visual Studio 2008?

  - by lividsquirrel

  When editing Silverlight XAML in Visual Studio 2008, the Document Outline panel is not supported by Microsoft. 1) Any helpful tip for navigating a deep XAML markup hierarchy without the benefit of the Document Outline tool? 2) Is this supported in Visual Studio 2010?

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• Issue in exec method

  - by mukul sharma

  Hi all, I am a having two python files file1.py and file2.py. I am using exec() to get the method/Variables defined in the file2.py. file1.py have a class as given below class one: def init(self): self.HOOK = None exec(file2.py) self.HOOK = Generate ### call the hook method #### self.HOOK() file2.py looks like as (There is no class define in file2.py) def Generate() do 1 do 2 Hello() def hello() print "hello" Now the problem is as When i run script it is giving a error global name Hello not found. If i remove Hello() from Generate method in file2.py then its work fine. I cant use import file2.py in file1.py,because in file2.py the only one method name (Generate) is fix (its taken as requirement). So apart from Genarate method user can define any method and can call this in generate method, because this approach is not working so i have to write whole code into generate method only and code is also repetitive. Any help is really appreciable...

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