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  • Number of different elements in an array.

    - by AB
    Is it possible to compute the number of different elements in an array in linear time and constant space? Let us say it's an array of long integers, and you can not allocate an array of length sizeof(long). P.S. Not homework, just curious. I've got a book that sort of implies that it is possible.

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  • C#: How to inherit constructors?

    - by Ian Boyd
    Imagine a base class with many constructors and a virtual method public class Foo { ... public Foo() {...} public Foo(int i) {...} ... public virtual void SomethingElse() {...} ... } and now I want to create a descendant class that overrides the virtual method: public class Bar : Foo { public override void SomethingElse() {...} } And another descendant that does some more stuff: public class Bah : Bar { public void DoMoreStuff() {...} } Do I really have to copy all constructors from Foo into Bar and Bah? And then if I change a constructor signature in Foo, do I have to update it in Bar and Bah? Is there no way to inherit constructors? Is there no way to encourage code reuse?

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  • Automatic testing of GUI related private methods

    - by Stein G. Strindhaug
    When it comes to GUI programming (at least for web) I feel that often the only thing that would be useful to unit test is some of the private methods*. While unit testing makes perfect sense for back-end code, I feel it doesn't quite fit the GUI classes. What is the best way to add automatic testing of these? * Why I think the only methods useful to test is private: Often when I write GUI classes they don't even have any public methods except for the constructor. The public methods if any is trivial, and the constructor does most of the job calling private methods. They receive some data from server does a lot of trivial output and feeds data to the constructor of other classes contained inside it, adding listeners that calls a (more or less directly) calls the server... Most of it pretty trivial (the hardest part is the layout: css, IE, etc.) but sometimes I create some private method that does some advanced tricks, which I definitely do not want to be publicly visible (because it's closely coupled to the implementation of the layout, and likely to change), but is sufficiently complicated to break. These are often only called by the constructor or repeatedly by events in the code, not by any public methods at all. I'd like to have a way to test this type of methods, without making it public or resorting to reflection trickery. (BTW: I'm currently using GWT, but I feel this applies to most languages/frameworks I've used when coding for GUI)

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  • Why can't I pass self as a named argument to an instance method in Python?

    - by Joseph Garvin
    This works: >>> def bar(x, y): ... print x, y ... >>> bar(y=3, x=1) 1 3 And this works: >>> class foo(object): ... def bar(self, x, y): ... print x, y ... >>> z = foo() >>> z.bar(y=3, x=1) 1 3 And even this works: >>> foo.bar(z, y=3, x=1) 1 3 But why doesn't this work? >>> foo.bar(self=z, y=3, x=1) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unbound method bar() must be called with foo instance as first argument (got nothing instead) This makes metaprogramming more difficult, because it requires special case handling. I'm curious if it's somehow necessary by Python's semantics or just an artifact of implementation.

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  • What does 'foo' really mean?

    - by Prakash
    I hope this qualifies as a programming question, as in any programming tutorial, you eventually come across 'foo' in the code examples. (yeah, right?) what does 'foo' really mean? If it is meant to mean nothing, when did it begin to be used so? Cheers

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  • Text message (SMS) verification for signups

    - by Unknown
    I have seen a disturbing trend where websites are starting to require verification sent to cellphones by text message (SMS). Gmail and Facebook are two of them. What I want to know are the following: Is it a good idea to start requiring cellphones instead of emails now? How do I do it on my own website? Edit Here are some of my new questions on the topic in response to the answers: I see that most of you are saying that SMS registrations is ok. But what about the people who don't have cell phones? And why is it accepted to give out your cell phone information freely? Do those big providers really pay per message to a gateway service? Is it not possible to set up a server with the correct SMS software, or at least buy a subscription directly instead of having a middleman?

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  • Where do you start your design - code, UI, workflow or whatever?

    - by Mmarquee
    Hi I was discussing this at work, and was wondering where people start their designs? We tend to start with designing code to solve the problem presented to us, but that is probably all of us are (or were) programmers. I was wondering where other people and organisations start their design. Do they start with solving the problem as a coding problem, sit down and design what UI to use, or map out the data or workflow? Thanks

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  • How do we achieve "substring-match" under O(n) time?

    - by Pacerier
    I have an assignment that requires reading a huge file of random inputs, for example: Adana Izmir Adnan Menderes Apt Addis Ababa Aden ADIYAMAN ALDAN Amman Marka Intl Airport Adak Island Adelaide Airport ANURADHAPURA Kodiak Apt DALLAS/ADDISON Ardabil ANDREWS AFB etc.. If I specify a search term, the program is supposed to find the lines whereby a substring occurs. For example, if the search term is "uradha", the program is supposed to show ANURADHAPURA. If the search term is "airport", the program is supposed to show Amman Marka Intl Airport, Adelaide Airport A quote from the assignment specs: "You are to program this application taking efficiency into account as though large amounts of data and processing is involved.." I could easily achieve this functionality using a loop but the performance would be O(n). I was thinking of using a trie but it seems to only work if the substring starts from index 0. I was wondering what solutions are there which gives a performance better than O(n)?

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  • C# internal VS VBNET Friend

    - by Will Marcouiller
    To this SO question: What is the C# equivalent of friend?, I would personally have answered "internal", just like Ja did among the answers! However, Jon Skeet says that there is no direct equivalence of VB Friend in C#. If Jon Skeet says so, I won't be the one telling otherwise! ;P I'm wondering how can the keyword internal (C#) not be the equivalent of Friend (VBNET) when their respective definitions are: Friend VBNET The Friend (Visual Basic) keyword in the declaration statement specifies that the elements can be accessed from within the same assembly, but not from outside the assembly. [...] internal C# Internal: Access is limited to the current assembly. To my understanding, these definitions mean quite the same to me. Then, respectively, when I'm coding in VB.NET, I use the Friend keyword to specify that a class or a property shall be accessible only within the assembly where it is declared. The same in C#, I use the internal keyword to specify the same. Am I doing something or anything wrong from this perspective? What are the refinements I don't get? Might someone please explain how or in what Friend and internal are not direct equivalences? Thanks in advance for any of your answers!

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  • What is meant by porting an application X to a platform Y ?

    - by Neeraj
    Pretty clear from the title itself, what is meant by porting an application X to a platform Y? Say for example I have an application X running on some OS, say Y, What do I do to port this application to another OS say Z? Does this mean rewriting a new application A for Operating system Z that necessarily imitates the behavior of application X on Operating System Y. Please explain.

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  • How do you tell if two wildcards overlap?

    - by Tom Ritter
    Given two strings with * wildcards, I would like to know if a string could be created that would match both. For example, these two are a simple case of overlap: Hello*World Hel* But so are all of these: *.csv reports*.csv reportsdump.csv Is there an algorithm published for doing this? Or perhaps a utility function in Windows or a library I might be able to call or copy?

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  • When is a good time to start thinking about scaling?

    - by Slokun
    I've been designing a site over the past couple days, and been doing some research into different aspects of scaling a site horizontally. If things go as planned, in a few months (years?) I know I'd need to worry about scaling the site up and out, since the resources it would end up consuming would be huge. So, this got me to thinking, when is the best time to start thinking about, and designing for, scalability? If you start too early on, you could easily over complicate your design, and make it impossible to actually build. You could also get too caught up in the details, the architecture, whatever, and wind up getting nothing done. Also, if you do get it working, but the site never takes off, you may have wasted a good chunk of extra effort. On the other hand, you could be saving yourself a ton of effort down the road. Designing it from the ground up to be big would make it much easier later on to let it grow big, with very little rewriting going on. I know for what I'm working on, I've decided to make at least a few choices now on the side of scaling, but I'm not going to do a complete change of thinking to get it to scale completely. Notably, I've redesigned my database from a conventional relational design to one similar to what was suggested on the Reddit site linked below, and I'm going to give memcache a try. So, the basic question, when is a good time to start thinking or worrying about scaling, and what are some good designs, tips, etc. for when doing so? A couple of things I've been reading, for those who are interested: http://www.codinghorror.com/blog/2009/06/scaling-up-vs-scaling-out-hidden-costs.html http://highscalability.com/blog/2010/5/17/7-lessons-learned-while-building-reddit-to-270-million-page.html http://developer.yahoo.com/performance/rules.html

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  • Technical choices in unmarshaling hash-consed data

    - by Pascal Cuoq
    There seems to be quite a bit of folklore knowledge floating about in restricted circles about the pitfalls of hash-consing combined with marshaling-unmarshaling of data. I am looking for citable references to these tidbits. For instance, someone once pointed me to library aterm and mentioned that the authors had clearly thought about this and that the representation on disk was bottom-up (children of a node come before the node itself in the data stream). This is indeed the right way to do things when you need to re-share each node (with a possible identical node already in memory). This re-sharing pass needs to be done bottom-up, so the unmarshaling itself might as well be, too, so that it's possible to do everything in a single pass. I am in the process of describing difficulties encountered in our own context, and the solutions we found. I would appreciate any citable reference to the kind of aforementioned folklore knowledge. Some people obviously have encountered the problems before (the aterm library is only one example). But I didn't find anything in writing. Even the little piece of information I have about aterm is hear-say. I am not worried it's not reliable (you can't make this up), but "personal communication" and "look how it's done in the source code" are considered poor form in citations. I have enough references on hash-consing alone. I am only interested in references where it interferes with other aspects of programming, such as marshaling or distribution.

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  • The Implications of Modern Day Software Development Abstractions

    - by Andreas Grech
    I am currently doing a dissertation about the implications or dangers that today's software development practices or teachings may have on the long term effects of programming. Just to make it clear: I am not attacking the use abstractions in programming. Every programmer knows that abstractions are the bases for modularity. What I want to investigate with this dissertation are the positive and negative effects abstractions can have in software development. As regards the positive, I am sure that I can find many sources that can confirm this. But what about the negative effects of abstractions? Do you have any stories to share that talk about when certain abstractions failed on you? The main concern is that many programmers today are programming against abstractions without having the faintest idea of what the abstraction is doing under-the-covers. This may very well lead to bugs and bad design. So, in you're opinion, how important is it that programmers actually know what is going below the abstractions? Taking a simple example from Joel's Back to Basics, C's strcat: void strcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); } The above function hosts the issue that if you are doing string concatenation, the function is always starting from the beginning of the dest pointer to find the null terminator character, whereas if you write the function as follows, you will return a pointer to where the concatenated string is, which in turn allows you to pass this new pointer to the concatenation function as the *dest parameter: char* mystrcat( char* dest, char* src ) { while (*dest) dest++; while (*dest++ = *src++); return --dest; } Now this is obviously a very simple as regards abstractions, but it is the same concept I shall be investigating. Finally, what do you think about the issue that schools are preferring to teach Java instead of C and Lisp ? Can you please give your opinions and your says as regards this subject? Thank you for your time and I appreciate every comment.

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  • Articles about replication schemes/algorithms?

    - by jkff
    I'm designing an hierarchical distributed system (every node has zero or more "master" nodes to which it propagates its current data). The data gets continuously updated and I'd like to guarantee that at least N nodes have almost-current data at any given time. I do not need complete consistency, only eventual consistency (t.i. for any time instant, the current snapshot of data should eventually appear on at least N nodes. It is tricky to define the term "current" here, but still). Nodes may fail and go back up at any moment, and there is no single "central" node. O overflowers! Point me to some good papers describing replication schemes. I've so far found one: Consistency Management in Optimistic Replication Algorithms

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  • The Definitive Guide To Website Authentication (beta)

    - by Michiel de Mare
    Form Based Authentication For Websites Please help us create the definitive resource for this topic. We believe that stackoverflow should not just be a resource for very specific technical questions, but also for general guidelines on how to solve variations on common problems. "Form Based Authentication For Websites" should be a fine topic for such an experiment. It should include topics such as: how to log in how to remain logged in how to store passwords using secret questions forgotten password functionality OpenID "Remember me" checkbox Browser autocompletion of usernames and passwords secret urls (public urls protected by digest) checking password strength email validation and much more It should not include things like: roles and authorization http basic authentication Please help us by Suggesting subtopics Submitting good articles about this subject Editing the official answer (as soon as you have enough karma) UPDATE: See the terrific 7-part series by Jens Roland below.

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  • Why do Pascal control structures appear to be inconsistent?

    - by 70Mike
    Most Pascal control structures make sense to me, like: for ... do {statement}; if (condition) then {statement}; while (condition) do {statement}; where the {statement} is either a single statement, or a begin ... end block. I have a problem with: repeat {statement-list} until (expression); try {statement-list} except {statement-list} end; Wouldn't it be better that repeat and try have the same general structure, accepting only a single statement or a begin ... end block, instead of having a statement-list that's not formally blocked with a begin and an end?

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  • Do you ever feel confident in your skills?

    - by Gary Willoughby
    As a self taught developer i always find myself questioning my skill and knowledge and always feel like i am falling behind in using new technology. Over a period of nearly 9 years i've studied most mainstream languages (especially C based ones), used lots of different OSes, read and absorbed many books and even written one myself. But i still feel i'm usless! Do professional developers ever get to the stage where they feel confident that they know what they are doing and are confident when submitting solutions/code? When do you know you're good enough?

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  • Nested class with hidden constructor impossible in c#?

    - by luckyluke
    I' ve been doing some programming lately and faced an issue which i found weird in c#. (at least for me) public class Foo { //whatever public class FooSpecificCollection : List<Bar> { //implementation details } public FooSpecificCollection GetFoosStuff() { //return the collection } } I want the consumer of Foo to be able to obtain a reference to FooSpecificCollection, even perform some operations on it. Maybe even set it to some other property of Foo or smth like that, but not To be able to CREATE an instance of this class. (the only class that should be able to instatiate this collection should be Foo. Is my request really that far-fetched? I know that people way smarter defined c# but shouldn't there be such an option that a parent class can create a nested class instance but nobody else can't. So far I created a solution to make an abstract class, or interface available through the property and implement a concrete private class that is not available anywhere else. Is this a correct way to handle such a situation.?

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  • .NET: How to pass value when subscribing to event and obtain it when the event is triggered (Dynamic

    - by Entrase
    The task is to create event handlers in runtime. I need the one method to be called with different parameter value for different events. The events and their number are only known in runtime. So I'm trying to generate dynamic methods, each of which will be assigned to some event, but in general they all just pass some value to an instance method and call it. It would be great if something similar could be done the easier way. I mean passing some value at subscribing stage and then obtaining it when the event is triggered. This is what I'm trying to do now: public class EventSource { public event EventHandler eventOne; public event EventHandler eventTwO; public event EventHandler eventThree; } public class EventListener { SubscribeForEvents() { BindingFlags flags = BindingFlags.IgnoreCase | BindingFlags.Public | BindingFlags.Instance; // Suppose we've already got EventInfo // and target source somewhere // so we can do eventInfo.AddEventHandler(target, delegate) // Now we need a delegate. int value = 42; Type tDelegate = eventInfo.EventHandlerType; // http://msdn.microsoft.com/en-us/library/ms228976(VS.95).aspx Type returnType = GetDelegateReturnType(tDelegate); DynamicMethod listener = new DynamicMethod("", null, GetDelegateParameterTypes(tDelegate), this.GetType()); ///////// Type[] callParameters = { typeof(int) }; MethodInfo method = this.GetType().GetMethod("ToCallFromDelegate", flags); ILGenerator generator = listener.GetILGenerator(); // No success in this mess. What's wrong? generator.Emit(OpCodes.Ldc_I4, value); generator.Emit(OpCodes.Call, method); generator.Emit(OpCodes.Pop); generator.Emit(OpCodes.Ret); ///////////// Delegate delegate = listener.CreateDelegate(tDelegate); eventInfo.AddEventHandler(target, delegate); // When triggered, there is InvalidProgramException } void ToCallFromDelegate(int value) { doSomething(); } }

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