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  • Should I use the ref or out keyword here?

    - by Blankman
    I have an object that may be null, which I will pass to a method that will set its properties. So my code looks like: User user = null; // may or may not be null at this point. SetUserProperties(user); UpdateUser(user); public void SetUserProperties(User user) { if(user == null) user = new User(); user.Firstname = "blah"; .... } So I am updating the same object I pass into SetUserProperties. Should I use the 'ref' keyword in my method SetUserProperties?

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  • Java Properties and References -- I'm not getting what I expect.

    - by Blumer
    I'm a little embarrassed to ask this as I ought to know better, but here's what I've got. I have an object "Pitcher" with an int property of "runsAllowed". I have an object Batter that has a property of "responsiblePitcher". I have an object Team that has a property "pitcher". When the batter reaches base: Batter.responsiblePitcher = Team.pitcher; All that's well and good. However, if we have a pitching change while the runner is on base, I set a new pitcher in Team.pitcher: Team.pitcher = new Pitcher(); ... and of course this changes the value of Batter.pitcher. How should I be doing things differently such that the Batter.responsiblePitcher property continues to point to the pitcher who let him on base instead of pointing at whever is in the Team.pitcher property? Again, I feel like I ought to know this already ... Thanks.

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  • javascript "this" points to Window object again

    - by terrani
    Hello, I asked a question on http://stackoverflow.com/questions/2719643/javascript-this-points-to-window-object regarding "this" points to Window object. here is source code var archive = function(){} archive.prototype.action = { test: function(callback){ callback(); }, test2: function(){ console.log(this); } } var oArchive = new archive(); oArchive.action.test(oArchive.action.test2); Tim Down wrote "but that function is then called using callback(), which means it is not called as a method and hence this is the global object". What are differences between calling a function by its actual name and callback() as shown on the source code? How does console.log(this) in test2 points to Window when it is inside archive.action???

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  • Custom login in Django

    - by alpgs
    Django newbie here. I wrote simplified login form which takes email and password. It works great if both email and password are supplied, but if either is missing i get KeyError exception. According to django documentation this should never happen: By default, each Field class assumes the value is required, so if you pass an empty value -- either None or the empty string ("") -- then clean() will raise a ValidationError exception I tried to write my own validators for fields (clean_email and clean_password), but it doesn't work (ie I get KeyError exception). What am I doing wrong? class LoginForm(forms.Form): email = forms.EmailField(label=_(u'Your email')) password = forms.CharField(widget=forms.PasswordInput, label=_(u'Password')) def clean_email(self): data = self.cleaned_data['email'] if not data: raise forms.ValidationError(_("Please enter email")) return data def clean_password(self): data = self.cleaned_data['password'] if not data: raise forms.ValidationError(_("Please enter your password")) return data def clean(self): try: username = User.objects.get(email__iexact=self.cleaned_data['email']).username except User.DoesNotExist: raise forms.ValidationError(_("No such email registered")) password = self.cleaned_data['password'] self.user = auth.authenticate(username=username, password=password) if self.user is None or not self.user.is_active: raise forms.ValidationError(_("Email or password is incorrect")) return self.cleaned_data

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  • C# 4.0 'dynamic' doesn't set ref/out arguments

    - by Buu Nguyen
    I'm experimenting with DynamicObject. One of the things I try to do is setting the values of ref/out arguments, as shown in the code below. However, I am not able to have the values of i and j in Main() set properly (even though they are set correctly in TryInvokeMember()). Does anyone know how to call a DynamicObject object with ref/out arguments and be able to retrieve the values set inside the method? class Program { static void Main(string[] args) { dynamic proxy = new Proxy(new Target()); int i = 10; int j = 20; proxy.Wrap(ref i, ref j); Console.WriteLine(i + ":" + j); // Print "10:20" while expect "20:10" } } class Proxy : DynamicObject { private readonly Target target; public Proxy(Target target) { this.target = target; } public override bool TryInvokeMember(InvokeMemberBinder binder, object[] args, out object result) { int i = (int) args[0]; int j = (int) args[1]; target.Swap(ref i, ref j); args[0] = i; args[1] = j; result = null; return true; } } class Target { public void Swap(ref int i, ref int j) { int tmp = i; i = j; j = tmp; } }

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  • Initializing objects on the fly

    - by pocoa
    I have a vector called players and a class called Player. And what I'm trying to do is to write: players.push_back(Player(name, Weapon(bullets))); So I want to be able to create players in a loop. But I see an error message says "no matching function for call Player::Player..." Then I've changed that to: Weapon w(bullets); Player p(name, w); players.push_back(p); Here is my Player definition: class Player { public: Player(string &name, Weapon &weapon); private string name; Weapon weapon; } I'm just trying to learn what is the difference between these definitions. And is this the right way to pass an object to an object constructor. Note: These are not my actual class definitions. I'm just trying to learn something about object oriented programming in C++ with coding it. I mean I know that Weapon should be initialized in Player :)

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  • What should a conference newbie bring to make the most out of their first conference?

    - by skarnis
    I am planning to attend my first developer conference (Microsoft TechDays 2008 in Toronto). I have been looking around for suggestions so that I can prepare and make the most out of my first developer conference. Many articles make suggestions about asking questions, getting involved, being social. These are great! I am also wondering about physical items. I have seen many conference photos with most of the audience having their laptops. Are they just taking notes? Are they working on a problem during the session? Are these photos just during a break and everyone is catching up on blogs/email/outside contact? Thank you StackOverflow-ers (StackOverflow-ites?)

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  • In the following implementation of static_strlen, why are the & and parentheses around str necessary

    - by Ben
    If I change the type to const char str[Len], I get the following error: error: no matching function for call to ‘static_strlen(const char [5])’ Am I correct that static_strlen expects an array of const char references? My understanding is that arrays are passed as pointers anyway, so what need is there for the elements to be references? Or is that interpretation completely off-the-mark? #include <iostream> template <size_t Len> size_t static_strlen(const char (&str)[Len]) { return Len - 1; } int main() { std::cout << static_strlen("oyez") << std::endl; return 0; }

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  • Using the word "you" in an user manual

    - by yan bellavance
    I am writing a user manual and I have come to a discussion with a colleague. He says I cannot use the word "you" anywhere in the manual. Now I remember something about this at school but that was not for writing procedures. Also, doing some googling I observed that most tutorials where using it a lot. I would prefer using it but only if this is considered good practice. what do you think?

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  • Could I be writing this code better?

    - by Ben Dauphinee
    Is there any website out there somewhere where a programmer such as myself might be able to post pieces of code to be looked at by more experienced people? I am thinking of something that programmers could use to have advice given on how to improve their ability. I really like the atmosphere here, but am not sure that posting code for review here is appropriate.

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  • Returning object from function

    - by brainydexter
    I am really confused now on how and which method to use to return object from a function. I want some feedback on the solutions for the given requirements. Scenario A: The returned object is to be stored in a variable which need not be modified during its lifetime. Thus, const Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { const Foo& l_Foo = someClassPInstance->GetFoo(); //... } Scneraio B: The returned object is to be stored in a variable which will be modified during its lifetime. Thus, void SomeClass::GetFoo(Foo& a_Foo_ref) { a_Foo_ref = Foo(); } invoked as: someMethod() { Foo l_Foo; someClassPInstance-GetFoo(l_Foo); //... } I have one question here: Lets say that Foo cannot have a default constructor. Then how would you deal with that in this situation, since we cant write this anymore: Foo l_Foo Scenario C: Foo SomeClass::GetFoo() { return Foo(); } invoked as: someMethod() { Foo l_Foo = someClassPInstance->GetFoo(); //... } I think this is not the recommended approach since it would incur constructing extra temporaries. What do you think ? Also, do you recommend a better way to handle this instead ?

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  • how to write a constructor...

    - by Nima
    is that correct to write a constructor like this? class A { A::A(const A& a) { .... } }; if yes, then is it correct to invoke it like this: A* other; ... A* instance = new A(*(other)); if not, what do you suggest? Thanks

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  • Are there any code critique sites or similar resources?

    - by Ukko
    I have noticed when people post example code illustrating some issue that they are having often they will gather a number of comments addressing the quality of the code they presented and not the actual problem asked. This is very helpful--if not well directed. Often, this is wasted effort since the asker is often not receptive and the code is often chopped down to something small to post leaving lots of rough edges. In the old days you would see people asking questions like this on comp.lang.lisp and other parts of the comp.lang hierarchy. But that bit of the net kind of sank into the sewers of neglect. Is there a comparable one-stop-shop today? I am partially asking for selfish reasons, I know how to write good idiomatic C, Lisp, O'Caml, and Java code. But I learned C++ pre-template and STL, those rusty skills are not really applicable to today's C++. I have picked up languages like Scala in a vacuum and get by, but am I really doing it correctly? There are so many ways you can abuse a language, I am currently working against a codebase of Fortran written in C, and I recognize and loathe the "that guy" who wrote it. I don't want to be someone else's "that guy" if I can help it. Just because it works does not mean that one did not totally miss the boat on how it should have been done. Do you seek out this type of critique? If so how, where and why? What types of benefits do you derive from it? How about abuse and trolls?

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  • Sharing common class in wcf project

    - by Saint
    class MyCommonClass { //properties } This class should be accessible in service project wcf-client project the other for which they are references. In this common project I can't generate servicereferences. I think, I could don't generate MyCommonClass in ServiceReferences but how to mark class to be nonserializable? In properties there's IgnoreDataMemberAttribute. I tried also reuse MyCommonClass type located in common project, but it is still generated

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  • What Do You Need To Write Your Own Blog Engine?

    - by deworde
    I've been messing around with basic websites for a few years, using companies like www.Fasthosts.co.uk to do my web hosting. But I'd like to expand my skills from C++ and Java app programming into Web-based programming, and I think the best way to do that is with a project. I've chosen to go with a blog engine because it's a relative comprehensive yet non-complex project. I'm aware that you can just go to Blogger and bam! One blog. I've done that, so that I can at least have some content, and work out what I want to do with this blog. At the moment, I'm thinking I'll use it to chart my progress creating the blogging engine. But I have some questions. Do you need to be running your own server? Or is it more sensible in the short-term to use a hosting company? What types of language are worth considering? What's important to focus on from a design perspective? What unexpected problems might I encounter?

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  • Becoming a professional PHP programmer. How?

    - by Abaco
    Hello there, I'm working on my first professional project. The fact is that I don't know which are the best tools to produce something serious (I'm talking about web-develop through PHP): Are template engine like Smarty mandatory? Which one is "the best" (the most used, complete, documentated) At the moment I'm developing on Notepad++ (mostly because I find it useful and complete) is there a better development tool? Or is just a matter of personal taste? At the moment I'm studying JQuery and deepening my knowledge as regards CSS what other "mandatory" subjects can you suggest me? This is what I can think of at the moment, have you any other suggestions? Thank you.

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  • "Home" of Javascript similar to python.org?

    - by drewk
    Perl, Ruby, Python, Javascript / ecmascript, PHP are all similar in the sense of being open source, open documentation, multi-platform, etc. Perl has http://www.perl.org Ruby has http://www.ruby-lang.org Python has http://www.python.org PHP has http://php.net Is there a "home" for javascript in the same sense as these other languages? When I say "home" I mean the go-to place for official documentation, specifications, source code of the language, examples, etc.

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  • Output is different for R-value and L-value. Why?

    - by Leonid Volnitsky
    Can someone explain to me why output for R-value is different from L-value? #include <iostream> #include <vector> using namespace std; template<typename Ct> struct ct_wrapper { Ct&& ct; // R or L ref explicit ct_wrapper(Ct&& ct) : ct(std::forward<Ct>(ct)) { std::cout << this->ct[1];}; }; int main() { // L-val vector<int> v{1,2,3}; ct_wrapper<vector<int>&> lv(v); cout << endl << lv.ct[0] << lv.ct[1] << lv.ct[2] << endl; // R-val ct_wrapper<vector<int>&&> rv(vector<int>{1,2,3}); cout << endl << rv.ct[0] << rv.ct[1] << rv.ct[2] << endl; } Output (same for gcc48 and clang32): 2 123 2 003

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  • Function with parameter type that has a copy-constructor with non-const ref chosen?

    - by Johannes Schaub - litb
    Some time ago I was confused by the following behavior of some code when I wanted to write a is_callable<F, Args...> trait. Overload resolution won't call functions accepting arguments by non-const ref, right? Why doesn't it reject in the following because the constructor wants a Test&? I expected it to take f(int)! struct Test { Test() { } // I want Test not be copyable from rvalues! Test(Test&) { } // But it's convertible to int operator int() { return 0; } }; void f(int) { } void f(Test) { } struct WorksFine { }; struct Slurper { Slurper(WorksFine&) { } }; struct Eater { Eater(WorksFine) { } }; void g(Slurper) { } void g(Eater) { } // chooses this, as expected int main() { // Error, why? f(Test()); // But this works, why? g(WorksFine()); } Error message is m.cpp: In function 'int main()': m.cpp:33:11: error: no matching function for call to 'Test::Test(Test)' m.cpp:5:3: note: candidates are: Test::Test(Test&) m.cpp:2:3: note: Test::Test() m.cpp:33:11: error: initializing argument 1 of 'void f(Test)' Can you please explain why one works but the other doesn't?

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  • what is this 'content_type' mean..

    - by zjm1126
    content_type = ContentType.objects.get_for_model(Map) maps = maps.extra(select=SortedDict([ ('member_count', MEMBER_COUNT_SQL), ('topic_count', TOPIC_COUNT_SQL), ]), select_params=(content_type.id,)) and the ContentType is: class ContentType(models.Model): name = models.CharField(max_length=100) app_label = models.CharField(max_length=100) model = models.CharField(_('python model class name'), max_length=100) objects = ContentTypeManager() class Meta: verbose_name = _('content type') verbose_name_plural = _('content types') db_table = 'django_content_type' ordering = ('name',) unique_together = (('app_label', 'model'),) def __unicode__(self): return self.name def model_class(self): "Returns the Python model class for this type of content." from django.db import models return models.get_model(self.app_label, self.model) def get_object_for_this_type(self, **kwargs): """ Returns an object of this type for the keyword arguments given. Basically, this is a proxy around this object_type's get_object() model method. The ObjectNotExist exception, if thrown, will not be caught, so code that calls this method should catch it. """ return self.model_class()._default_manager.using(self._state.db).get(**kwargs) def natural_key(self): return (self.app_label, self.model) i want to know: what is the 'content_type' used for ??

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  • What's a reasonable way to mutate a primitive variable from an anonymous Java class?

    - by Steve
    I would like to write the following code: boolean found = false; search(new SearchCallback() { @Override void onFound(Object o) { found = true; } }); Obviously this is not allowed, since found needs to be final. I can't make found a member field for thread-safety reasons. What is the best alternative? One workaround is to define final class MutableReference<T> { private T value; MutableReference(T value) { this.value = value; } T get() { return value; } void set(T value) { this.value = value; } } but this ends up taking a lot of space when formatted properly, and I'd rather not reinvent the wheel if at all possible. I could use a List<Boolean> with a single element (either mutating that element, or else emptying the list) or even a Boolean[1]. But everything seems to smell funny, since none of the options are being used as they were intended. What is a reasonable way to do this?

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  • WCF Web/ServiceHost - Singletons and initialisation

    - by Kyle
    I have some Service class which is defined as InstanceContextMode.Single, and is well known in the hosting application. (The host creates an instance, and passes that to the WebServiceHost) Hosting app:WebServiceHost host = null; SomeService serviceInstance = new SomeService("text", "more text"); host = new WebServiceHost(serviceInstance, baseUri); Problem: When I go to use the variables initialised when the service is created (ie, when a call is made to the service), they are either null or empty... Am I wrong in assuming that as the instance being initialised in the hosting application is used for each request to the WebServiceHost? Any pointers here would be great.

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  • How to learn Haskell

    - by anderstornvig
    For a few days I've tried to wrap my head around the functional programming paradigm in Haskell. I've done this by reading tutorials and watching screencasts, but nothing really seems to stick. Now, in learning various imperative/OO languages (like C, Java, PHP), excercises have been a good way for me to go. But since I don't really know what Haskell is capable of and because there are many new concepts to utilize, I haven't known where to start. So, how did you learn Haskell? What made you really "break the ice"? Also, any good ideas for beginning excercises?

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  • Delphi constants and references

    - by Sambatyon
    I want to pass constant references to functions in delphi, so I am sure that the referenced object won't change and to save time and memory. So I want to declare a function like function foo(var const Value : Bar) : Boolean; however this is not allowed. I thought constant values would be automatically sent as references. However I found out that it is not the case (getting the address of an object before sending it to the function gives me $12F50C and the address of the same object inside the function is $12F564) What can I do to send constant references?

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