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• Questions about my program and Polymorphism

  - by Strobe_

  Ok, so basically I'm creating a program which allows the user to select a shape (triangle, square, circle) and then it takes in a int and calculates the boundary length and area. I have no problem doing this and have a program that's working perfectly. (https://gist.github.com/anonymous/c63a03c129560a7b7434 4 classes) But now I have to implement this with polymorphism concepts and I'm honestly struggling as to how to do it. I have a basic idea of what I want to do when it comes to inheritance Main | Shapes / | \ triangle circle square But I don't understand how I'm supposed to override when all the methods within the triangle/square/circle classes are unique, there are no "abstract" methods as such that I could inherit from the "Shapes" class. If somebody could make look quickly at the code I linked and suggest a way to do this it would be much appreciated. Sorry if I was bad at explaining this. Thanks.

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• How to get global access to enum types in C#?

  - by lala

  This is probably a stupid question, but I can't seem to do it. I want to set up some enums in one class like this: public enum Direction { north, east, south, west }; Then have that enum type accessible to all classes so that some other class could for instance have: Direction dir = north; and be able to pass the enum type between classes: public void changeDirection(Direction direction) { dir = direction; } I thought that setting the enum to public would make this automatically possible, but it doesn't seem to be visible outside of the class I declared the enum in.

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• How to deploy a Scala project from Eclipse?

  - by lach

  I have a Scala project in Eclipse that I need to package up so I can deploy it to a server. It's based on Jetty but it runs as a standalone application. It contains Scala classes, Java classes and a number of 3rd party jars. I assumed there would be some kind of deployment option in the Scala Eclipse plugin but I've drawn a blank. What is the simplest way to package the Scala project into a runnable file so it can be deployed? Any help greatly appreciated. Cheers.

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• Preallocating memory with C++ in realtime environment

  - by Elazar Leibovich

  I'm having a function which gets an input buffer of n bytes, and needs an auxillary buffer of n bytes in order to process the given input buffer. (I know vector is allocating memory at runtime, let's say that I'm using a vector which uses static preallocated memory. Imagine this is NOT an STL vector.) The usual approach is void processData(vector<T> &vec) { vector<T> &aux = new vector<T>(vec.size()); //dynamically allocate memory // process data } //usage: processData(v) Since I'm working in a real time environment, I wish to preallocate all the memory I'll ever need in advance. The buffer is allocated only once at startup. I want that whenever I'm allocating a vector, I'll automatically allocate auxillary buffer for my processData function. I can do something similar with a template function static void _processData(vector<T> &vec,vector<T> &aux) { // process data } template<size_t sz> void processData(vector<T> &vec) { static aux_buffer[sz]; vector aux(vec.size(),aux_buffer); // use aux_buffer for the vector _processData(vec,aux); } // usage: processData<V_MAX_SIZE>(v); However working alot with templates is not much fun (now let's recompile everything since I changed a comment!), and it forces me to do some bookkeeping whenever I use this function. Are there any nicer designs around this problem?

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• How can I configure different worker pools using celery?

  - by Chris R

  I need to deploy a queued execution service with (generally) the following three classes of worker: A periodic, low-priority job class that takes a long time and can be processed serially; these jobs should only use 0..2 workers in the system at most. A periodic, deadline-sensitive job class that take a short to medium amount of time (say, topping out at 5 minutes) An ad-hoc job class, that is higher priority than #1, but can interleave with #2. Any workers from class #2 that are inactive when this type of job comes in should handle it, without ever starving the pool of workers for #2 All three job classes are the same task, the only difference between them is how they're requested; they'll take the same input and generate the same output, but each one has different performance guarantees. How can I implement this using celery?

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• What's the most straightforward way to typeset MLA-style college essays in LaTeX?

  - by bcat

  I've been using LaTeX for a little while now to typeset my algorithms homework, and I really like the quality of the output as well as the ease-of-use. I'd like to starting using LaTeX in other classes as well, but non–computer-science subjects have more stringent formatting requirements than I've come across in CS. Most classes that require essays want them to be formatted in MLA style, but I'm not sure what to best way to do that using LaTeX is. I've tried Googling "latex mla" and other similar things, but I've found many different MLA templates, and my LaTeX skills aren't good enough to determine which is the best. Is anyone else using LaTeX for "normal" essays, and, if so, how are you doing it?

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• Why are these lines being skipped? (java)

  - by David

  Here's the relevant bit of the source code: class Dice { String name ; int x ; int[] sum ; ... public Dice (String name) { this.name = name ; this.x = 0 ; this.sum = new int[7] ; } ... public static void main (String[] arg) { Dice a1 = new Dice ("a1") ; printValues (a1) ; } public static void printDice (Dice Dice) { System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; printValues (Dice) ; } public static void printValues (Dice Dice) { for (int i = 0; i<Dice.sum.length; i++) System.out.println ("#of "+i+"'s: "+Dice.sum[i]) ; } } Here is the output: #of 0's: 0 #of 1's: 0 #of 2's: 0 #of 3's: 0 #of 4's: 0 #of 5's: 0 #of 6's: 0 Why didn't these two lines execute inside printDice: System.out.println (Dice.name) ; System.out.println ("value: "+Dice.x) ; if they had then i would expect to see "a1" and "Value: 0" printed at the top of the rows of #of's

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• Pass Session data to a Class Library without using a bunch of constructors?

  - by sah302

  Hi all, I've got my application here where literally every object has a lastUpdatedBy property. The information I put into here is the person's username, which is retrieved from the session("username") variable. How can I pass this data to my DAL in the class library? At first I was just passing in the value into each method, but this is ridiculous I thought, there should be no reason to do that every time a method is called. Then I thought well if I just put it in a constructor for each of the DAL related classes, that will make it even easier. However, even still on any given page, I've got a plethora of New() declarations, for which every single line I need to pass in the session username casted as a string. Is there an even still more efficient way of doing this so that I could only declare this in one place, and everything will know what it is and I can pass it to classes in a class library?

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• Does Qt support virtual pure slots ?

  - by ereOn

  Hi, My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget. Recently, I realized that all these classes share 2 commons slots (loadSettings() and saveSettings()). Regarding this, I have two questions: Does it make sense to write a intermediate base abstract class (lets name it BaseConfigurationPage) with these two slots as virtual pure methods ? (Every possible configuration page will always have these two methods, so I would say "yes") Before I do the heavy change in my code (if I have to) : does Qt support virtual pure slots ? Is there anything I should be aware of ? Here is a code example describing everything: class BaseConfigurationPage : public QWidget { // Some constructor and other methods, irrelevant here. public slots: virtual void loadSettings() = 0; virtual void saveSettings() = 0; }; class GeneralConfigurationPage : public BaseConfigurationPage { // Some constructor and other methods, irrelevant here. public slots: void loadSettings(); void saveSettings(); };

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• How to make command-line options mandatory with GLib?

  - by ahe

  I use GLib to parse some command-line options. The problem is that I want to make two of those options mandatory so that the program terminates with the help screen if the user omits them. My code looks like this: static gint line = -1; static gint column = -1; static GOptionEntry options[] = { {"line", 'l', 0, G_OPTION_ARG_INT, &line, "The line", "L"}, {"column", 'c', 0, G_OPTION_ARG_INT, &column, "The column", "C"}, {NULL} }; ... int main(int argc, char** argv) { GError *error = NULL; GOptionContext *context; context = g_option_context_new ("- test"); g_option_context_add_main_entries (context, options, NULL); if (!g_option_context_parse(context, &argc, &argv, &error)) { usage(error->message, context); } ... return 0; } If I omit one of those parameters or both on the command-line g_option_context_parse() still succeeds and the values in question (line and or column) are still -1. How can I tell GLib to fail parsing if the user doesn't pass both options on the command-line? Maybe I'm just blind but I couldn't find a flag I can put into my GOptionEntry data structure to tell it to make those fields mandatory. Of course I could check if one of those variables is still -1 but then the user could just have passed this value on the command-line and I want to print a separate error message if the values are out of range.

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• Is there a way to get the list of InnerClasses through Reflection in Java?

  - by kunjaan

  Is there a way to know the inner classes that a Class has through Reflection in Java?

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• How does compiler use lib file ?

  - by Xinus

  I am curious about how c/c++ compiler analyse lib files ? I mean say I create a library containing some classes, I am using that library in my main program. How does compiler know what class names are there in that library. Of course that information is present in binary format, I want to use that functionality in my program, to be specific I have a binary lib file and I want to know all classes and properties/functions present in that lib file. Is it possible ? If compiler can do that why can't some library ? thanks for any clue

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• When is a try catch not a try catch?

  - by Dearmash

  I have a fun issue where during application shutdown, try / catch blocks are being seemingly ignored in the stack. I don't have a working test project (yet due to deadline, otherwise I'd totally try to repro this), but consider the following code snippet. public static string RunAndPossiblyThrow(int index, bool doThrow) { try { return Run(index); } catch(ApplicationException e) { if(doThrow) throw; } return ""; } public static string Run(int index) { if(_store.Contains(index)) return _store[index]; throw new ApplicationException("index not found"); } public static string RunAndIgnoreThrow(int index) { try { return Run(index); } catch(ApplicationException e) { } return ""; } During runtime this pattern works famously. We get legacy support for code that relies on exceptions for program control (bad) and we get to move forward and slowly remove exceptions used for program control. However, when shutting down our UI, we see an exception thrown from "Run" even though "doThrow" is false for ALL current uses of "RunAndPossiblyThrow". I've even gone so far as to verify this by modifying code to look like "RunAndIgnoreThrow" and I'll still get a crash post UI shutdown. Mr. Eric Lippert, I read your blog daily, I'd sure love to hear it's some known bug and I'm not going crazy. EDIT This is multi-threaded, and I've verified all objects are not modified while being accessed

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• how can access public properties of MasterPage from external Class ?

  - by eugeneK

  Why i can't access MasterPage's public property (MessagePlaceholder) from other Class (Errors) ? Error compiler gives me is "Error 1 The type or namespace name 'MyMasterPage' could not be found (are you missing a using directive or an assembly reference?)" my master page code behind using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; public partial class MyMasterPage : System.Web.UI.MasterPage { public string MessagePlaceholder { get { return messagePlaceholder.InnerHtml; } set { messagePlaceholder.InnerHtml = value; } } protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { messagePlaceholder.InnerHtml = Errors.getMessage(); } } } my Errors Class public static string getMessage() { HttpContext c = HttpContext.Current; string messageType = ""; if (c.Session["errorMessage"] != null) { messageType = "errorMessage"; } else if (c.Session["successMessage"] != null) { messageType = "successMessage"; } if (!string.IsNullOrEmpty(messageType)) { StringBuilder userMessageSb = new StringBuilder(); userMessageSb.Append(string.Format("<div id=\"{0}\" title=\"{1}\">{2}</div>", messageType, messageType.Replace("Message",string.Empty), c.Session[messageType])); // fix so message will not re-appear c.Session.Remove(messageType); messageType = userMessageSb.ToString(); } return messageType; } public static void setSuccess(string successMessage, bool isRedirect) { HttpContext.Current.Session["successMessage"] = successMessage; } public static void setError(string errorMessage, bool isRedirect) { HttpContext.Current.Session["errorMessage"] = errorMessage; if (!isRedirect) { ((HttpContext.Current.CurrentHandler as System.Web.UI.Page).Master as MyMasterPage).MessagePlaceholder = getMessage(); } } this is how i set error if (true) { Errors.setError("this is an error demo", false); return; } or with redirect after error if (true) { Errors.setError("yet another error", true); Response.Redirect("~/error.aspx"); }

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• What to return as an iterator when there is no container?

  - by DaClown

  I have an inheritance structure of objects with begin() and end() as pure virtual member functions in the base class. From this objects I'm planning to build a composite structure. This inner objects have std::vector member the begin() and end() get their data from. But in a leaf class there is no vector. Now I try to find a return value for begin() and end() in the leaf classes. What would be a good way to do that? The easiest way would be to have a vector member in the leaf classes with no elements in it to fuel begin() and end(), but this just doesn't feel right.

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• 'is instanceof' Interface bad design

  - by peterRit

  Say I have a class A class A { Z source; } Now, the context tells me that 'Z' can be an instance of different classes (say, B and C) which doesn't share any common class in their inheritance tree. I guess the naive approach is to make 'Z' an Interface class, and make classes B and C implement it. But something still doesn't convince me because every time an instance of class A is used, I need to know the type of 'source'. So all finishes in multiple 'ifs' making 'is instanceof' which doesn't sound quite nice. Maybe in the future some other class implements Z, and having hardcoded 'ifs' of this type definitely could break something. The escence of the problem is that I cannot resolve the issue by adding functions to Z, because the work done in each instance type of Z is different. I hope someone can give me and advice, maybe about some useful design pattern. Thanks

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• What is the difference between these two linq implementations?

  - by Mahesh Velaga

  I was going through Jon Skeet's Reimplemnting Linq to Objects series. In the implementation of where article, I found the following snippets, but I don't get what is the advantage that we are gettting by splitting the original method into two. Original Method: // Naive validation - broken! public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Refactored Method: public static IEnumerable<TSource> Where<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { if (source == null) { throw new ArgumentNullException("source"); } if (predicate == null) { throw new ArgumentNullException("predicate"); } return WhereImpl(source, predicate); } private static IEnumerable<TSource> WhereImpl<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate) { foreach (TSource item in source) { if (predicate(item)) { yield return item; } } } Jon says - Its for eager validation and then defferring for the rest of the part. But, I don't get it. Could some one please explain it in a little more detail, whats the difference between these 2 functions and why will the validations be performed in one and not in the other eagerly? Conclusion/Solution: I got confused due to my lack of understanding on which functions are determined to be iterator-generators. I assumed that, it is based on signature of a method like IEnumerable<T>. But, based on the answers, now I get it, a method is an iterator-generator if it uses yield statements.

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• How To Collapse Just One Field in Django Admin?

  - by Apreche

  The django admin allows you to specify fieldsets. You properly structure a tuple that groups different fields together. You can also specify classes for certain groups of fields. One of those classes is collapse, which will hide the field under a collapsable area. This is good for hiding rarely used or advanced fields to keep the UI clean. However, I have a situation where I want to hide just one lonesome field on many different apps. This will be a lot of typing to create a full fieldset specification in every admin.py file just to put one field into the collapsed area. It also creates a difficult maintenance situation because I will have to edit the fieldset every time I edit the associated model. I can easily exclude the field entirely using the exclude option. I want something similar for collapse. Is this possible?

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• Is it possible to specify a return type of "Derivative(of T)" for a MustOverride sub in VB.NET?

  - by Casey

  VB.NET 2008 .NET 3.5 I have two base classes that are MustInherit (partial). Let's call one class OrderBase and the other OrderItemBase. A specific type of order and order item would inherit from these classes. Let's call these WebOrder (inherits from OrderBase) and WebOrderItem (inherits from OrderItemBase). Now, in the grand scheme of things WebOrder is a composite class containing a WebOrderItem, like so: Public Class WebOrder Inherits OrderBase Public Property OrderItem() as WebOrderItem End Property End Class Public Class WebOrderItem Inherits OrderItemBase End Class In order to make sure any class that derives from OrderBase has the OrderItem property, I would like to do something like this in the OrderBase class: Public MustInherit Class OrderBase Public MustOverride Property OrderItem() as Derivative(Of OrderItemBase) End Class In other words, I want the derived class to be forced to contain a property that returns a derivative of OrderItemBase. Is this possible, or should I be using an entirely different approach?

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• C++ Multiple Inheritance Question

  - by John

  The scenario generating this is quite complex so I'll strip out a few pieces and give an accurate representation of the classes involved. /* This is inherited using SI by many classes, as normal */ class IBase { virtual string toString()=0; }; /* Base2 can't inherit IBase due to other methods on IBase which aren't appropriate */ class Base2 { string toString() { ... } }; /* a special class, is this valid? */ class Class1 : public IBase, public Base2 { }; So, is this valid? Will there be conflicts on the toString? Or can Class1 use Base2::toString to satisfy IBase? Like I say there are lots of other things not shown, so suggestions for major design changes on this example are probably not that helpful... though any general suggestions/advice are welcome.

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• Do you use another language instead of english ?

  - by Luc M

  Duplicate Should identifiers and comments be always in English or in the native language of the application and developers? For people who are not native English speakers, which language do you use to declare variables, classes, etc. ? I had to continue a project from a Spanish guy. Everything was written in Spanish. Since this time, I have decided to use English identifiers ( variables, classes, file names) and write comments in french. Everything was in french before that. What are the general recommendations about that practice? Do you use English everywhere knowing that no English people will work on your project ? Edit : Here's a post from Jeff Atwood about this subject: The Ugly American Programmer

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• Separation of domain and ui layer in a composite

  - by hansmaad

  Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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• Is there a way to get the list of InnerClasses throught Reflection in Java?

  - by kunjaan

  Is there a way to know the inner classes that a Class has through Reflection in Java?

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• C# 3 dimensional array definition issue

  - by George2

  Hello everyone, My following code has compile error, Error 1 Cannot implicitly convert type 'TestArray1.Foo[,,*]' to 'TestArray1.Foo[][][]' C:\Users\lma\Documents\Visual Studio 2008\Projects\TestArray1\TestArray1\Program.cs 17 30 TestArray1 Does anyone have any ideas? Here is my whole code, I am using VSTS 2008 + Vista 64-bit. namespace TestArray1 { class Foo { } class Program { static void Main(string[] args) { Foo[][][] foos = new Foo[1, 1, 1]; return; } } } EDIT: version 2. I have another version of code, but still has compile error. Any ideas? Error 1 Invalid rank specifier: expected ',' or ']' C:\Users\lma\Documents\Visual Studio 2008\Projects\TestArray1\TestArray1\Program.cs 17 41 TestArray1 Error 2 Invalid rank specifier: expected ',' or ']' C:\Users\lma\Documents\Visual Studio 2008\Projects\TestArray1\TestArray1\Program.cs 17 44 TestArray1 namespace TestArray1 { class Foo { } class Program { static void Main(string[] args) { Foo[][][] foos = new Foo[1][1][1]; return; } } } EDIT: version 3. I think I want to have a jagged array. And after learning from the fellow guys. Here is my code fix, and it compile fine in VSTS 2008. What I want is a jagged array, and currently I need to have only one element. Could anyone review whether my code is correct to implement my goal please? namespace TestArray1 { class Foo { } class Program { static void Main(string[] args) { Foo[][][] foos = new Foo[1][][]; foos[0] = new Foo[1][]; foos[0][0] = new Foo[1]; foos[0][0][0] = new Foo(); return; } } } thanks in advance, George

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• Factorial function - design and test.

  - by lukas

  I'm trying to nail down some interview questions, so I stared with a simple one. Design the factorial function. This function is a leaf (no dependencies - easly testable), so I made it static inside the helper class. public static class MathHelper { public static int Factorial(int n) { Debug.Assert(n >= 0); if (n < 0) { throw new ArgumentException("n cannot be lower that 0"); } Debug.Assert(n <= 12); if (n > 12) { throw new OverflowException("Overflow occurs above 12 factorial"); } //by definition if (n == 0) { return 1; } int factorialOfN = 1; for (int i = 1; i <= n; ++i) { //checked //{ factorialOfN *= i; //} } return factorialOfN; } } Testing: [TestMethod] [ExpectedException(typeof(OverflowException))] public void Overflow() { int temp = FactorialHelper.MathHelper.Factorial(40); } [TestMethod] public void ZeroTest() { int factorialOfZero = FactorialHelper.MathHelper.Factorial(0); Assert.AreEqual(1, factorialOfZero); } [TestMethod] public void FactorialOf5() { int factOf5 = FactorialHelper.MathHelper.Factorial(5); Assert.AreEqual(120,factOf5); } [TestMethod] [ExpectedException(typeof(ArgumentException))] public void NegativeTest() { int factOfMinus5 = FactorialHelper.MathHelper.Factorial(-5); } I have a few questions: Is it correct? (I hope so ;) ) Does it throw right exceptions? Should I use checked context or this trick ( n 12 ) is ok? Is it better to use uint istead of checking for negative values? Future improving: Overload for long, decimal, BigInteger or maybe generic method? Thank you

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