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  • C++ inheritance and member function pointers

    - by smh
    In C++, can member function pointers be used to point to derived (or even base) class members? EDIT: Perhaps an example will help. Suppose we have a hierarchy of three classes X, Y, Z in order of inheritance. Y therefore has a base class X and a derived class Z. Now we can define a member function pointer p for class Y. This is written as: void (Y::*p)(); (For simplicity, I'll assume we're only interested in functions with the signature void f() ) This pointer p can now be used to point to member functions of class Y. This question (two questions, really) is then: Can p be used to point to a function in the derived class Z? Can p be used to point to a function in the base class X?

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  • Rails 3 find all associated records has_many :through

    - by Sergey
    I would like to list all posts that are connected with some specific category. I have: class Post < ActiveRecord::Base has_many :category_posts has_many :categories, :through => :category_posts end class Category < ActiveRecord::Base has_many :category_posts has_many :posts, :through => :category_posts end class CategoryPost < ActiveRecord::Base belongs_to :category belongs_to :post end And I wanna do something like this Post.where(["category.id = ?", params[:category_id]]) It indeed is very simple task, but I don't know what I should be looking for (keywords). It's the same problem like this, but in rails.

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  • improving drawing pythagoras tree

    - by sasquatch90
    Hello. I have written program for drawing pythagoras tree fractal. Can anybody see any way of improving it ? Now it is 120 LOc. I was hoping to shorten it to ~100... import javax.swing.*; import java.util.Scanner; import java.awt.Color; import java.awt.Dimension; import java.awt.Graphics; import javax.swing.JComponent; public class Main extends JFrame {; public Main(int n) { setSize(900, 900); setTitle("Pythagoras tree"); Draw d = new Draw(n); add(d); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setVisible(true); } private int pow(int n){ int pow = 2; for(int i = 1; i < n; i++){ if(n==0){ pow = 1; } pow = pow*2; } return pow; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); System.out.print("Give amount of steps: "); int steps = sc.nextInt(); new Main(steps); } } class Draw extends JComponent { private int height; private int width; private int steps; public Draw(int n) { height = 800; width = 800; steps = n; Dimension d = new Dimension(width, height); setMinimumSize(d); setPreferredSize(new Dimension(d)); setMaximumSize(d); } @Override public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.white); g.fillRect(0, 0, width, height); g.setColor(Color.black); int w = width; int h = height; int x1, x2, x3, x4, x5, y1, y2, y3, y4, y5; int base = w/7; x1 = (w/2)-(base/2); x2 = x1; x3 = (w/2)+(base/2); x4 = x3; x5 = w/2; y1 = (h-(h/15))-base; y2 = h-(h/15); y3 = y2; y4 = y1; y5 = (h-(h/15))-(base+(base/2)); //paint g.drawLine(x1, y1, x2, y2); g.drawLine(x2, y2, x3, y3); g.drawLine(x3, y3, x4, y4); g.drawLine(x1, y1, x4, y4); int n1 = steps; n1--; if(n1>0){ g.drawLine(x1, y1, x5, y5); g.drawLine(x4, y4, x5, y5); paintMore(n1, g, x1, x5, x4, y1, y5, y4); paintMore(n1, g, x4, x5, x1, y4, y5, y1); } } public void paintMore(int n1, Graphics g, double x1_1, double x2_1, double x3_1, double y1_1, double y2_1, double y3_1){ double x1, x2, x3, x4, x5, y1, y2, y3, y4, y5; //counting x1 = x1_1 + (x2_1-x3_1); x2 = x1_1; x3 = x2_1; x4 = x2_1 + (x2_1-x3_1); x5 = ((x2_1 + (x2_1-x3_1)) + ((x2_1-x3_1)/2)) + ((x1_1-x2_1)/2); y1 = y1_1 + (y2_1-y3_1); y2 = y1_1; y3 = y2_1; y4 = y2_1 + (y2_1-y3_1); y5 = ((y1_1 + (y2_1-y3_1)) + ((y2_1-y1_1)/2)) + ((y2_1-y3_1)/2); //paint g.setColor(Color.green); g.drawLine((int)x1, (int)y1, (int)x2, (int)y2); g.drawLine((int)x3, (int)y3, (int)x4, (int)y4); g.drawLine((int)x1, (int)y1, (int)x4, (int)y4); n1--; if(n1>0){ g.drawLine((int)x1, (int)y1, (int)x5, (int)y5); g.drawLine((int)x4, (int)y4, (int)x5, (int)y5); paintMore(n1, g, x1, x5, x4, y1, y5, y4); paintMore(n1, g, x4, x5, x1, y4, y5, y1); } } }

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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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  • Casting a container of shared_ptr

    - by Jamie Cook
    Hi all, I have a method void foo(list<shared_ptr<Base>>& myList); Which I'm trying to call with a two different types of lists, one of DerivedClass1 and one of DerivedClass2 list<shared_ptr<DerivedClass1>> myList1; foo(myList1); list<shared_ptr<DerivedClass2>> myList2; foo(myList2); However this obviously generates a compiler error error: a reference of type "std::list<boost::shared_ptr<Base>, std::allocator<boost::shared_ptr<Base>>> &" (not const-qualified) cannot be initialized with a value of type "std::list<boost::shared_ptr<DerivedClass1>, std::allocator<boost::shared_ptr<DerivedClass1>>>" Is there any easy way to cast a container of shared_ptr? Of alternate containers that can accomplish this?

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  • Can I db.put models without db.getting them first?

    - by Liron
    I tried to do something like ss = Screenshot(key=db.Key.from_path('myapp_screenshot', 123), name='flowers') db.put([ss, ...]) It seems to work on my dev_appserver, but on live I get this traceback: 05-07 09:50PM 19.964 File "/base/data/home/apps/quixeydev3/12.341796548761906563/common/appenginepatch/appenginepatcher/patch.py", line 600, in put E 05-07 09:50PM 19.964 result = old_db_put(models, *args, **kwargs) E 05-07 09:50PM 19.964 File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/db/init.py", line 1278, in put E 05-07 09:50PM 19.964 keys = datastore.Put(entities, rpc=rpc) E 05-07 09:50PM 19.964 File "/base/python_runtime/python_lib/versions/1/google/appengine/api/datastore.py", line 284, in Put E 05-07 09:50PM 19.965 raise _ToDatastoreError(err) E 05-07 09:50PM 19.965 InternalError: the new entity or index you tried to insert already exists I happen to know just the ID of an existing Screenshot entity I want to update; that's why I was manually constructing its key. Am I doing it wrong?

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  • How to call same method for a list of objects?

    - by Dmitry
    Suppose code like this: class Base: def start(self): pass def stop(self) pass class A(Base): def start(self): ... do something for A def stop(self) .... do something for A class B(Base): def start(self): def stop(self): a1 = A(); a2 = A() b1 = B(); b2 = B() all = [a1, b1, b2, a2,.....] Now I want to call methods start and stop (maybe also others) for each object in the list all. Is there any elegant way for doing this except of writing a bunch of functions like def start_all(all): for item in all: item.start() def stop_all(all): .....

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  • argparse coding issue

    - by Carl Skonieczny
    write a script that takes two optional boolean arguments,"--verbose‚" and ‚"--live", and two required string arguments, "base"and "pattern". Please set up the command line processing using argparse. This is the code I have so far for the question, I know I am getting close but something is not quite right. Any help is much appreciated.Thanks for all the quick useful feedback. def main(): import argparse parser = argparse.ArgumentParser(description='') parser.add_argument('base', type=str) parser.add_arguemnt('--verbose', action='store_true') parser.add_argument('pattern', type=str) parser.add_arguemnt('--live', action='store_true') args = parser.parse_args() print(args.base(args.pattern))

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  • Unreachable code detected in case statement

    - by alex
    I have a code: protected override bool ProcessCmdKey(ref Message msg, Keys keyData) { switch (keyData) { case Keys.Alt|Keys.D1: if (this._condition1) { return true; } else { return base.ProcessCmdKey(ref msg, keyData); } break; case Keys.Control |Keys.U: if (this._condition2) { return true; } else { return base.ProcessCmdKey(ref msg, keyData); } break; default: return base.ProcessCmdKey(ref msg, keyData); } return true; It gives me "unreachable code detected" warning on breaks. Is it good practice not to use break operator here ? I don't want to turn off "unreachable code detected" warning. PS: There are many case in my ProcessCmdKey method.

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  • Template inheritance: X is not a template

    - by user2923917
    I am trying to build a inheritance-structure which looks like: Base - template Grandpa - template Father class Base {}; template <int x> class Grandpa: public Base {}; template <int x> class Father: public Grandpa<x> {}; However, the compiler complains when compiling Father, that Grandpa is not a template. I guess it is just some synthatic issue, however everything I've tried so far led to even more compiler complaints ;) Any idea whats wrong?

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  • Returning a static array without using a class field

    - by Bart Friederichs
    I have the following base and derived (partial, for sake of brevity) classes: class Base { public abstract int[] someArray { get; } } class Derived : Base { private readonly static int[] _someArray = new int[] { 1,2,3,4 }; public override int[] someArray { get { return _someArray; } } } What I would like now, is put the new int[] { 1,2,3,4 } in the return part of the getter. But, that would create a new array every time the getter is called. Is it possible to directly return some kind of object, which stays the same for all objects of class Derived ? Something along the lines of (I know this is invalid C#): get { return (int[]) { 1, 2, 3, 4 }; }

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  • Are Ext JS files necessary in a working site?

    - by songdogtech
    I've inherited a high-traffic site that loads some Ext javascript files and I'm trying to trim some bandwidth usage. Are Ext libraries necessary for development only or are they required for the finished site (I've never used Ext.) The site loads ext-base.js, ext-all-debug.js, expander.js, exteditor.js. It appears that expander.js and exteditor.js have some site specific code, so they should stay? But what about ext-base.js and ext-all-debug.js? Am I reading this correctly - are base and debugging libraries necessary for a live site?

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  • In WPF, how do I update the object that my custom property is bound to?

    - by Timothy Khouri
    I have a custom property that works perfectly, except when it's bound to an object. The reason is that once the following code is executed: base.SetValue(ValueProperty, value); ... then my control is no longer bound. I know this because calling: base.GetBindingExpression(ValueProperty); ... returns the binding object perfectly - UNTIL I call base.SetValue. So my question is, how do I pass the new "value" on to the object that I'm bound to?

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  • Mix and match class in C++/MFC

    - by Coder
    I'm trying to re-factor a code base, and there is some common functionality among unrelated classes that I'd love to unite. I would like to add that functionality in common base class, but I'm not sure if it's clean and good approach. Say I have CMyWnd class and CMyDialogEx class, both different, so they cannot inherit from one base class. I want to add a button to both classes and add the message handlers to both classes as well. So I'd like to do something like this: CMyWnd : public CWnd, public COnOkBtnFunctionality, public COnCancelBtnFunctionality CMyDialogEx: public CWnd, public COnOkBtnFunctionality Where COnOkBtnFunctionality would define CButton m_buttonOk, and all the afx_msg functions it should have. And so on. Is this approach doable/good? Or are there better patterns I should resort to?

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  • Cannot send e-mail with rails 2.3.4(I could with 2.3.2)

    - by Brian Roisentul
    I'm working with ruby on rails 2.3.4 and I yesterday I found out I cannot send emails any more. The email-related credentials are ok because I could send emails until I upgraded my rails version about two weeks ago. The error message I get is the following: ArgumentError in UsersController#create wrong # of arguments(3 for 2) D:/Proyectos/Cursometro/www/vendor/plugins/action_mailer_tls/lib/smtp_tls.rb:8:in `check_auth_args' D:/Proyectos/Cursometro/www/vendor/plugins/action_mailer_tls/lib/smtp_tls.rb:8:in `do_start' C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/1.8/net/smtp.rb:525:in `start' C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/actionmailer-2.3.4/lib/action_mailer/base.rb:682:in `perform_delivery_smtp' C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/actionmailer-2.3.4/lib/action_mailer/base.rb:523:in `deliver!' C:/Program Files (x86)/NetBeans 6.8/ruby2/jruby-1.4.0/lib/ruby/gems/1.8/gems/actionmailer-2.3.4/lib/action_mailer/base.rb:395:in `method_missing' D:/Proyectos/Cursometro/www/app/models/user_observer.rb:3:in `after_create' D:/Proyectos/Cursometro/www/app/controllers/users_controller.rb:221:in `create_new_user' D:/Proyectos/Cursometro/www/app/controllers/users_controller.rb:101:in `create' Please, help!

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  • User HasOne ActiveToken, HasMany Tokens, how to setup in Rails?

    - by viatropos
    I have two simple models: class User < ActiveRecord::Base has_many :tokens # has_one doesn't work, because Token already stores # foreign id to user... # has_one :active_token, :class_name => "Token" # belongs_to doesn't work because Token belongs to # User already, and they both can't belong to each other # belongs_to :active_token, :class_name => "Token" end class Token < ActiveRecord::Base belongs_to :user end I want to say "User has_one :active_token, :class_name => 'Token'", but I can't because Token already belongs_to User. What I did instead was just manually add similar functionality to the user like so: class User < ActiveRecord::Base has_many :tokens attr_accessor :active_token after_create :save_active_token before_destroy :destroy_active_token # it belongs_to, but you can't have both belongs_to each other... def active_token return nil unless self.active_token_id @active_token ||= Token.find(self.active_token_id) end def active_token=(value) self.active_token_id = value.id @active_token = value end def save_active_token self.active_token.user = self self.active_token.save end def destroy_active_token self.active_token.destroy if self.active_token end end Is there a better way?

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  • Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • Setting new class variables inside a module

    - by Sean McCleary
    I have a plugin I have been working on that adds publishing to ActiveRecord classes. I extend my classes with my publisher like so: class Note < ActiveRecord::Base # ... publishable :related_attributes => [:taggings] end My publisher is structured like: module Publisher def self.included(base) base.send(:extend, ClassMethods) @@publishing_options = [] # does not seem to be available end module ClassMethods def publishable options={} include InstanceMethods @@publishing_options = options # does not work as class_variable_set is a private method # self.class_variable_set(:@@publishing_options, options) # results in: uninitialized class variable @@publishing_options in Publisher::ClassMethods puts "@@publishing_options: #{@@publishing_options.inspect}" # ... end # ... end module InstanceMethods # results in: uninitialized class variable @@publishing_options in Publisher::InstanceMethods def related_attributes @@publishing_options[:related_attributes] end # ... end end Any ideas on how to pass options to publishable and have them available as a class variable?

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  • [C++] Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • I'm getting the following error ''expected an indented block'' Where is the failing code?

    - by user1833814
    import math def area(base, height): '''(number,number) -> number Return the area of a wirh given base and height. >>>area(10,40) 200.0 ''' return base * height / 2 def perimeter(side1, side2, side3): '''(number,number,number) -> number Return the perimeter of the triangle with sides of length side1,side2 and side3. >>>perimeter(3,4,5) 12 >>>perimeter(10.5,6,9.3) 25.8 ''' return (side1 + side2 + side3) def semiperimeter(side1, side2, side3): return perimeter(side1, side2, side3) / 2 def area_hero(side1, side2, side3): semi = semiperimeter(side1, side2, side3) area = math.sqrt((semi * (semi - side1) * (semi - side2) * (semi - side3)) return area

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  • Problems with ActiveRecord assoc

    - by ciss
    Hello again, so i write my e-commerce shop cms and have some strange error: ActiveRecord::StatementInvalid: Mysql::Error: Unknown column 'id' in 'where clause': DELETE FROM `properties` WHERE `id` = NULL so, i have three models Items: class Item < ActiveRecord::Base has_many :properties, :dependent => :destroy has_many :types, :through => :property end Type: class Type < ActiveRecord::Base has_many :properties, :dependent => :destroy end Properties: class Property < ActiveRecord::Base belongs_to :item belongs_to :type end So, all is okay, but when i try to item.destroy() i have error =( This is my test code: test "should destroy associated properties" do item = Item.create(:name => "Jeans") type = Type.create(:key => "color") property = Property.new property.item = item property.type = type property.save item.destroy() end

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  • Passing derived objects in a constructure

    - by Clarence Klopfstein
    This is a bit of a convoluted question, hopefully I can make it clear. I am finding that this may not be possible, but am trying to see if anybody has a solution. I have four classes, two are core classes and two are those core classes extended: extUser Extends coreUser extSecurity Extends coreSecurity In the constructor for coreUser you have this: public coreUser(string id, ref coreSecurity cs) When trying to extend coreUser you would have this: public extUser(string id ref extSecurity es) : base(id, ref es) This fails because es is of type, extSecurity and the base class expects a type of coreSecurity. I've not found anyway to cast this to allow for me to override this base class in C#. In VB it works just fine. Ideas?

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  • Rails 3 Order By Count on has_many :through

    - by goo
    I have an application where I can list Items and add tags to each Item. The models Items and Tags are associated like this: class Item < ActiveRecord::Base has_many :taggings has_many :tags, :through => :taggings end class Tagging < ActiveRecord::Base belongs_to :item belongs_to :tag end class Tag < ActiveRecord::Base has_many :taggings has_many :items, :through => :taggings end So, this many-to-many relationship allows me to set n tags for each Item, and the same tag can be used several times. I'd like to list all tags ordered by the number of items associated with this tag. More used tags, shows first. Less used, last. How can I do that? Regards.

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  • Using regular expressions with Dojo data.fetch?

    - by Dfowj
    I'm trying to use the below code to fetch a regular expression like this /[computer]{3,8}/(what i think is any words containing the letters in computer ranging from 3 to 8 letters long) from a database (which i know is being loaded correctly). When i fetch, i get 10 results, all the same word... "Adenauer" var base = "computer"; var baseRE = '/[' + base + ']{' + this.minLength + ',' + base.length + '}/'; this.dict.fetch({query: {word:baseRE}, onComplete: onLoadWords, onError: function(err) { console.log(err); }}); Any ideas what im doing wrong?

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  • C++ Inheritance Question

    - by shaz
    I have a base class MessageHandler and 2 derived classes, MessageHandler_CB and MessageHandler_DQ. The derived classes redefine the handleMessage(...) method. MH_DQ processes a message and puts the result in a deque while MH_CB processes the message and then executes a callback function. The base class has a static callback function that I pass along with a this pointer to a library which calls the static callback when a new message is available for processing. My problem comes when I am in the static callback with a void * pointing to either a MH_DQ or a MH_CB. If I cast it to the base class the empty MessageHandler::handleMessage(...) method is called, rather than the version in the appropriate derived class. What is the best way to address this situation from a design perspective and/or what language features might help me to implement a solution to my problem? Thanks in advance!

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