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  • If I never ever use HashSet, should I still implement GetHashCode?

    - by Dimitri C.
    I never need to store objects in a hash table. The reason is twofold: coming up with a good hash function is difficult and error prone. an AVL tree is almost always fast enough, and it merely requires a strict order predicate, which is much easier to implement. The Equals() operation on the other hand is a very frequently used function. Therefore I wonder whether it is necessary to implement GetHashCode (which I never need) when implementing the Equals function (which I often need)?

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  • empty base class optimization

    - by FredOverflow
    Two quotes from the C++ standard, §1.8: An object is a region of storage. Base class subobjects may have zero size. I don't think a region of storage can be of size zero. That would mean that some base class subobjects aren't actually objects. Opinions?

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  • Django: saving pickled object

    - by pistacchio
    Hi, i have a large dictionary I'd like to save. I have pickled it using cPickle.dumps and saved the result into a TextField. When trying to retrieve it (cPicle.loads) i get the following error: loads() argument 1 must be string, not unicode Does anybody have any experience in serializing python objects and storing them in a DB using Django? Thanks in advance.

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  • creating proxy object in groovy

    - by IttayD
    Hi, I am looking for how to write a method that accepts some value and returns a proxy to that value where the underlying value can be retrieved with an accessor: def p = toProxy(1) assert p == 1 assert p * 2 == 2 assert p.underlying == 1 def p2 = toProxy(objWithMethodFoo) p2.foo() p2.underlying.foo() I want to do this per object instance (not for all objects of some class) and without the need to use special 'use' constructs.

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  • Network Differences

    - by Chris
    I am busy working on a java app to run on blackberries but on some devices i am testing on, the code does not seem to be working and im having a hard time pinpointing where the problem lies. My question is: Could the problem with some phones working and not working have t odo with the type of network they are running on such GSM vs CDMA and would the code that stops working on some devices be in one of the following areas: 1) Listeners - such as MessageListener and Phone Listener 2) UI Objects - simple test labels and buttons 3) Connection to a web service using ksoap2

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  • What's the difference between C and C++

    - by Dinah
    I know that C++ has the concept of objects but C doesn't. I also know that pretty much all there is to know about C fits into K & R but the C++ library is vastly more complex. There have got to be other big differences though. What are the major differences between C and C++?

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  • XSD editor with the ability to write plugins in Python

    - by Tomasz Zielinski
    I'm writing a Python module for parsing XSD for very specific purpose. Currently it's a console program, but ideally I would see it plugged inside some XSD editor - not only for convenience of end users, but also for fetching XSD parsed into Python objects - this would save me days or weeks of work. Is there any such editor on the market?

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  • How to write unit tests for an object having multiple properties

    - by jess
    Hi, I have various objects in application,and each has isvalid method to test if values of all properties are set correctly(as per business rules).Now,to test that for each violation isvalid throws false,i will have to write as many tests as rules being checked in isvalid.Is there a simpler way to do this? I am using MBunit.

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  • JavaScript date comparisons

    - by Kyle
    I am new to the lower level useful functions of JavaScript, and I find myself needing to compare two date objects, but within an hourly range. For example, if Date1 is less then two hours until (or from) Date2. How could this be done?

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  • Operator overloading in generic struct: can I create overloads for specific kinds(?) of generic?

    - by Carson Myers
    I'm defining physical units in C#, using generic structs, and it was going okay until I got the error: One of the parameters of a binary operator must be the containing type when trying to overload the mathematical operators so that they convert between different units. So, I have something like this: public interface ScalarUnit { } public class Duration : ScalarUnit { } public struct Scalar<T> where T : ScalarUnit { public readonly double Value; public Scalar(double Value) { this.Value = Value; } public static implicit operator double(Scalar<T> Value) { return Value.Value; } } public interface VectorUnit { } public class Displacement : VectorUnit { } public class Velocity : VectorUnit { } public struct Vector<T> where T : VectorUnit { #... public static Vector<Velocity> operator /(Vector<Displacement> v1, Scalar<Duration> v2) { return new Vector<Velocity>(v1.Magnitude / v2, v1.Direction); } } There aren't any errors for the + and - operators, where I'm just working on a Vector<T>, but when I substitute a unit for T, suddenly it doesn't like it. Is there a way to make this work? I figured it would work, since Displacement implements the VectorUnit interface, and I have where T : VectorUnit in the struct header. Am I at least on the right track here? I'm new to C# so I have difficulty understanding what's going on sometimes.

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  • How to span multile tables in Django

    - by ipartola
    The Django documentation gives en example like so: b = Blog.objects.get(id=1) b.entry_set.all() Which from what I understand results in 2 queries. What if I wanted to get the blog, the blog entries and all the comments associated with that entry in a number of queries that does not depend on the number of entries? Or do I have to drop down to SQL to do that?

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  • Should the argument be passed by reference in this .net example?

    - by Hamish Grubijan
    I have used Java, C++, .Net. (in that order). When asked about by-value vs. by-ref on interviews, I have always done well on that question ... perhaps because nobody went in-depth on it. Now I know that I do not see the whole picture. I was looking at this section of code written by someone else: XmlDocument doc = new XmlDocument(); AppendX(doc); // Real name of the function is different AppendY(doc); // ditto When I saw this code, I thought: wait a minute, should not I use a ref in front of doc variable (and modify AppendX/Y accordingly? it works as written, but made me question whether I actually understand the ref keyword in C#. As I thought about this more, I recalled early Java days (college intro language). A friend of mine looked at some code I have written and he had a mental block - he kept asking me which things are passed in by reference and when by value. My ignorant response was something like: Dude, there is only one kind of arg passing in Java and I forgot which one it is :). Chill, do not over-think and just code. Java still does not have a ref does it? Yet, Java hackers seem to be productive. Anyhow, coding in C++ exposed me to this whole by reference business, and now I am confused. Should ref be used in the example above? I am guessing that when ref is applied to value types: primitives, enums, structures (is there anything else in this list?) it makes a big difference. And ... when applied to objects it does not because it is all by reference. If things were so simple, then why would not the compiler restrict the usage of ref keyword to a subset of types. When it comes to objects, does ref serve as a comment sort of? Well, I do remember that there can be problems with null and ref is also useful for initializing multiple elements within a method (since you cannot return multiple things with the same easy as you would do in Python). Thanks.

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  • Looking for an appropriate design pattern

    - by user1066015
    I have a game that tracks user stats after every match, such as how far they travelled, how many times they attacked, how far they fell, etc, and my current implementations looks somewhat as follows (simplified version): Class Player{ int id; public Player(){ int id = Math.random()*100000; PlayerData.players.put(id,new PlayerData()); } public void jump(){ //Logic to make the user jump //... //call the playerManager PlayerManager.jump(this); } public void attack(Player target){ //logic to attack the player //... //call the player manager PlayerManager.attack(this,target); } } Class PlayerData{ public static HashMap<int, PlayerData> players = new HashMap<int,PlayerData>(); int id; int timesJumped; int timesAttacked; } public void incrementJumped(){ timesJumped++; } public void incrementAttacked(){ timesAttacked++; } } Class PlayerManager{ public static void jump(Player player){ players.get(player.getId()).incrementJumped(); } public void incrementAttacked(Player player, Player target){ players.get(player.getId()).incrementAttacked(); } } So I have a PlayerData class which holds all of the statistics, and brings it out of the player class because it isn't part of the player logic. Then I have PlayerManager, which would be on the server, and that controls the interactions between players (a lot of the logic that does that is excluded so I could keep this simple). I put the calls to the PlayerData class in the Manager class because sometimes you have to do certain checks between players, for instance if the attack actually hits, then you increment "attackHits". The main problem (in my opinion, correct me if I'm wrong) is that this is not very extensible. I will have to touch the PlayerData class if I want to keep track of a new stat, by adding methods and fields, and then I have to potentially add more methods to my PlayerManager, so it isn't very modulized. If there is an improvement to this that you would recommend, I would be very appreciative. Thanks.

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  • Question about singleton property

    - by Jack
    I'm reading the java tutorial for enums located here and have a question: http://java.sun.com/j2se/1.5.0/docs/guide/language/enums.html#Card The part i'm confused about is as follows: "The Card class, above, contains a static factory that returns a deck, but there is no way to get an individual card from its rank and suit. Merely exposing the constructor would destroy the singleton property (that only a single instance of each card is allowed to exist). Here is how to write a static factory that preserves the singleton property, using a nested EnumMap: " Now as I understand, changing the original private "Card" constructor to public would allow us to instantiate an unlimited number of copies of a "Card" object with a given suit+rank. The solution as proposed was to create an EnumMap which would store four Maps (one for each suit), which themselves contained 13 Card objects with the rank as their keys. And so now if you wanted to retrieve a specific Card object from the deck, you would just call the "valueOf" method. My question now is, what's the prevent you with calling the valueOf method as many times as you like? Wouldn't that lead to the same problem as making the original private constructor public? Thanks.

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  • python: list manipulation

    - by Jason S
    I have a list L of objects (for what it's worth this is in scons). I would like to create two lists L1 and L2 where L1 is L with an item I1 appended, and L2 is L with an item I2 appended. I would use append but that modifies the original list. How can I do this in Python? (sorry for the beginner question, I don't use the language much, just for scons)

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  • Undo implementation - DOM manipulations

    - by sonofdelphi
    Is there a library that can be used for implementing undo/redo functionality for DOM element manipulations in JavaScript? I'm writing an app that moves around DOM elements, enables editing and deletion of those elements. There are event-handlers and other objects associated with each element operated upon. Not sure whether I need to roll my own implementation of the Command pattern for this. Surely, there must be something available? If not, suggestions and pointers would be a great help.

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  • Detect when a new property is added to a Javascript object?

    - by UICodes
    A simple example using a built-in javascript object: navigator.my_new_property = "some value"; //can we detect that this new property was added? I don't want to constantly poll the object to check for new properties. Is there some type of higher level setter for objects instead of explicitly stating the property to monitor? Again, I don't want to detect if the property value changed, but rather when a new property is added. Ideas? thanks

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  • Why can't your switch statement data type be long Java?

    - by Fostah
    Here's an excerpt from Sun's Java tutorials: A switch works with the byte, short, char, and int primitive data types. It also works with enumerated types (discussed in Classes and Inheritance) and a few special classes that "wrap" certain primitive types: Character, Byte, Short, and Integer (discussed in Simple Data Objects ). There must be a good reason why the long primitive data type is not allowed. Anyone know what it is?

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  • Access to and availability of private member functions in C++

    - by David
    I am wandering the desert of my brain. I'm trying to write something like the following: class MyClass { // Peripherally Related Stuff public: void TakeAnAction(int oneThing, int anotherThing) { switch(oneThing){ case THING_A: TakeThisActionWith(anotherThing); break; //cases THINGS_NOT_A: }; }; private: void TakeThisActionWith(int thing) { string outcome = new string; outcome = LookUpOutcome(thing); // Do some stuff based on outcome return; } string LookUpOutcome(int key) { string oc = new string; oc = MyPrivateMap[key]; return oc; } map<int, string> MyPrivateMap; Then in the .cc file where I am actually using these things, while compiling the TakeAnAction section, it [CC, the solaris compiler] throws an an error: 'The function LookUpOutcome must have a prototype' and bombs out. In my header file, I have declared 'string LookUpOutcome(int key);' in the private section of the class. I have tried all sorts of variations. I tried to use 'this' for a little while, and it gave me 'Can only use this in non-static member function.' Sadly, I haven't declared anything static and these are all, putatively, member functions. I tried it [on TakeAnAction and LookUp] when I got the error, but I got something like, 'Can't access MyPrivateMap from LookUp'. MyPrivateMap could be made public and I could refer to it directly, I guess, but my sensibility says that is not the right way to go about this [that means that namespace scoped helper functions are out, I think]. I also guess I could just inline the lookup and subsequent other stuff, but my line-o-meter goes on tilt. I'm trying desperately not to kludge it.

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  • Retrieving Data in A NSTableView

    - by Heisennberg
    I have a three column Table View populated by two NSMutableDictionaries which share the same keys (ie key | value1 | value2 ) with dict1(key,value1) and dict2(key,value2). I want to manually enter data in the third column and create the key/value objects in dict2. But when I do that, my code picks the wrong key :S Here's the code for the delegate : - (void)tableView:(NSTableView *)aTableView setObjectValue:(id)anObject forTableColumn:(NSTableColumn *)aTableColumn row:(NSInteger)rowIndex { if ([[aTableColumn identifier] isEqualToString:@"value2"]) { [dict2 setValue:anObject forKey:[[[aTableView tableColumnWithIdentifier:@"key"] dataCellForRow:rowIndex] stringValue ]]; } } Any idea ?

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  • Dispose, when is it called?

    - by Snake
    Consider the following code: namespace DisposeTest { using System; class Program { static void Main(string[] args) { Console.WriteLine("Calling Test"); Test(); Console.WriteLine("Call to Test done"); } static void Test() { DisposeImplementation di = new DisposeImplementation(); } } internal class DisposeImplementation : IDisposable { ~DisposeImplementation() { Console.WriteLine("~ in DisposeImplementation instance called"); } public void Dispose() { Console.WriteLine("Dispose in DisposeImplementation instance called"); } } } The Dispose just never get's called, even if I put a wait loop after the Test(); invocation. So that quite sucks. I want to write a class that is straightforward and very easy to use, to make sure that every possible resource is cleaned up. I don't want to put that responsibilty to the user of my class. Possible solution: use using, or call Dispose myself(basicly the same). Can I force the user to use a using? Or can I force the dispose to be called? Calling GC.Collect(); after Test(); doesn't work either. Putting di to null doesn't invoke Dispose either. The Deconstructor DOES work, so the object get's deconstructed when it exits Test()

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  • Query Entity Framework 4

    - by nick
    Hi, Is it possible to run a query on an EF4.0 data context and get all objects of a certain type? Say the context has books, genres & authors but I only have a generic parameter, t. Is it possible to get all of type just by using this t? I don't think it is :(

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