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• Should you declare methods using overloads or optional parameters in C# 4.0?

  - by Greg Beech

  I was watching Anders' talk about C# 4.0 and sneak preview of C# 5.0, and it got me thinking about when optional parameters are available in C# what is going to be the recommended way to declare methods that do not need all parameters specified? For example something like the FileStream class has about fifteen different constructors which can be divided into logical 'families' e.g. the ones below from a string, the ones from an IntPtr and the ones from a SafeFileHandle. FileStream(string,FileMode); FileStream(string,FileMode,FileAccess); FileStream(string,FileMode,FileAccess,FileShare); FileStream(string,FileMode,FileAccess,FileShare,int); FileStream(string,FileMode,FileAccess,FileShare,int,bool); It seems to me that this type of pattern could be simplified by having three constructors instead, and using optional parameters for the ones that can be defaulted, which would make the different families of constructors more distinct [note: I know this change will not be made in the BCL, I'm talking hypothetically for this type of situation]. What do you think? From C# 4.0 will it make more sense to make closely related groups of constructors and methods a single method with optional parameters, or is there a good reason to stick with the traditional many-overload mechanism?

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• Help me choose a web development framework/platform that will make me learn something

  - by Sergio Tapia

  I'm having a bit of an overload of information these past two days. I'm planning to start my own website that will allow local businesses to list their items on sale, and then users can come in and search for "Abercrombie t-shirt" and the stores that sell them will be listed. It's a neat little project I'm really excited for and I'm sure it'll take off, but I'm having problems from the get go. Sure I could use ASP.Net for it, I'm a bit familiar with it and the IDE for ASP.Net pages is bar-none, but I feel this is a great chance for me to learn something new to branch out a bit and not regurgitate .NET like a robot. I've been looking and asking around but it's all just noise and I can't make an educated decision. Can you help me choose a framework/platform that will make me learn something that's a nice thing to know in the job market, but also nice for me to grow as a professional? So far I've looked at: Ruby on Rails Kohana CakePHP CodeIgniter Symfony But they are all very esoteric to me, and I have trouble even finding out which IDE to use to that will let me use auto-complete for the proprietary keywords/methods. Thank you for your time.

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• Overloading operator>> to a char buffer in C++ - can I tell the stream length?

  - by exscape

  I'm on a custom C++ crash course. I've known the basics for many years, but I'm currently trying to refresh my memory and learn more. To that end, as my second task (after writing a stack class based on linked lists), I'm writing my own string class. It's gone pretty smoothly until now; I want to overload operator that I can do stuff like cin my_string;. The problem is that I don't know how to read the istream properly (or perhaps the problem is that I don't know streams...). I tried a while (!stream.eof()) loop that .read()s 128 bytes at a time, but as one might expect, it stops only on EOF. I want it to read to a newline, like you get with cin to a std::string. My string class has an alloc(size_t new_size) function that (re)allocates memory, and an append(const char *) function that does that part, but I obviously need to know the amount of memory to allocate before I can write to the buffer. Any advice on how to implement this? I tried getting the istream length with seekg() and tellg(), to no avail (it returns -1), and as I said looping until EOF (doesn't stop reading at a newline) reading one chunk at a time.

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• Call method immediately after object construction in LINQ query

  - by Steffen

  I've got some objects which implement this interface: public interface IRow { void Fill(DataRow dr); } Usually when I select something out of db, I go: public IEnumerable<IRow> SelectSomeRows { DataTable table = GetTableFromDatabase(); foreach (DataRow dr in table.Rows) { IRow row = new MySQLRow(); // Disregard the MySQLRow type, it's not important row.Fill(dr); yield return row; } } Now with .Net 4, I'd like to use AsParallel, and thus LINQ. I've done some testing on it, and it speeds up things alot (IRow.Fill uses Reflection, so it's hard on the CPU) Anyway my problem is, how do I go about creating a LINQ query, which calls Fills as part of the query, so it's properly parallelized? For testing performance I created a constructor which took the DataRow as argument, however I'd really love to avoid this if somehow possible. With the constructor in place, it's obviously simple enough: public IEnumerable<IRow> SelectSomeRowsParallel { DataTable table = GetTableFromDatabase(); return from DataRow dr in table.Rows.AsParallel() select new MySQLRow(dr); } However like I said, I'd really love to be able to just stuff my Fill method into the LINQ query, and thus not need the constructor overload.

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• Populating dropdownlist in asp.net mvc doesn't seem to work for me...

  - by Pandiya Chendur

  I use a dropdownlist in one of my create.aspx but it some how doesnt seem to work... public IEnumerable<Materials> FindAllMeasurements() { var mesurements = from mt in db.MeasurementTypes select new Materials() { Id= Convert.ToInt64(mt.Id), Mes_Name= mt.Name }; return mesurements; } and my controller, public ActionResult Create() { var mesurementTypes = consRepository.FindAllMeasurements().AsEnumerable(); ViewData["MeasurementType"] = new SelectList(mesurementTypes, "Id", "Mes_Name"); return View(); } and my create.aspx has this, <p> <label for="MeasurementTypeId">MeasurementType:</label> <%= Html.DropDownList("MeasurementType", ViewData["MeasurementType"])%> <%= Html.ValidationMessage("MeasurementTypeId", "*") %> </p> When i execute this i got these errors, System.Web.Mvc.HtmlHelper<CrMVC.Models.Material>' does not contain a definition for 'DropDownList' and the best extension method overload 'System.Web.Mvc.Html.SelectExtensions.DropDownList(System.Web.Mvc.HtmlHelper, string, System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>)' has some invalid arguments 2.cannot convert from 'object' to 'System.Collections.Generic.IEnumerable<System.Web.Mvc.SelectListItem>

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• Adroid's DateFormat replacement - missing the format() with FieldPosition

  - by user331244

  Hi, I need to split a date string into pieces and I'm doing it using the public final StringBuffer format (Object object, StringBuffer buffer, FieldPosition field) from the java.text.DateFormat class. However, the implementation of this function is really slow, hence Android has an own implementation in android.text.format.DateFormat. BUT, in my case, I want to extract the different pieces of the date string (year, minute and so on). Since I need to be locale independent, I can not use SimpleDateFormat and custom strings. I do it as follows: Calendar c = ... // find out what field to extract int field = getField(); // Create a date string Field calendarField = DateFormat.Field.ofCalendarField(field); FieldPosition fieldPosition = new FieldPosition(calendarField); StringBuffer label = new StringBuffer(); label = getDateFormat().format(c.getTime(), label, fieldPosition); // Find the piece that we are looking for int beginIndex = fieldPosition.getBeginIndex(); int endIndex = fieldPosition.getEndIndex(); String asString = label.substring(beginIndex, endIndex); For some reason, the format() overload with the FieldPosition argument is not included in the android platform. Any ideas of how to do this in another way? Is there any easy way to tokenize the pattern string? Any other ideas?

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• invasive vs non-invasive ref-counted pointers in C++

  - by anon

  For the past few years, I've generally accepted that if I am going to use ref-counted smart pointers invasive smart pointers is the way to go -- However, I'm starting to like non-invasive smart pointers due to the following: I only use smart pointers (so no Foo* lying around, only Ptr) I'm starting to build custom allocators for each class. (So Foo would overload operator new). Now, if Foo has a list of all Ptr (as it easily can with non-invasive smart pointers). Then, I can avoid memory fragmentation issues since class Foo move the objects around (and just update the corresponding Ptr). The only reason why this Foo moving objects around in non-invasive smart pointers being easier than invasive smart pointers is: In non-invasive smart pointers, there is only one pointer that points to each Foo. In invasive smart pointers, I have no idea how many objects point to each Foo. Now, the only cost of non-invasive smart pointers ... is the double indirection. [Perhaps this screws up the caches]. Does anyone have a good study of expensive this extra layer of indirection is?

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• How to use html.grid control in spark view for asp.net mvc?

  - by Anusha

  class person() { public int Id{get;set;} public string Name{get;set;} } HomeController.cs ActionResult Index() { IList list=new[]{ new person { Id = 1, Name = "Name1" }, new person { Id = 2, Name = "Name2" }, new person { Id = 3, Name = "Name3" } }; ViewData["mygrid"]=list; return view(); } Home\Index.spark !{Html.Grid[[person]]("mygrid", (column=>{ column.For(c=>c.Id); column.For(c=>c.Name); })) Am getting the error Dynamic view compilation failed..error CS1501: No overload for method 'Grid' takes '2' arguments. I have added reference to MvcContrib.dll And added following namespace in the _global.spark file <use namespace="MvcContrib.UI"/> <use namespace="MvcContrib.UI.Grid"/> <use namespace="MvcContrib.UI.Pager"/> <use namespace="MvcContrib.UI.Grid.ActionSyntax"/> <use namespace="Microsoft.Web.Mvc.Controls"/> I want to bind the data to my grid in spark view.Can anybody help.

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• high cpu in IIS

  - by Miki Watts

  Hi all. I'm developing a POS application that has a local database on each POS computer, and communicates with the server using WCF hosted in IIS. The application has been deployed in several customers for over a year now. About a week ago, we've started getting reports from one of our customers that the server that the IIS is hosted on is very slow. When I've checked the issue, I saw the application pool with my process rocket to almost 100% cpu on an 8 cpu server. I've checked the SQL Activity Monitor and network volume, and they showed no significant overload beyond what we usually see. When checking the threads in Process Explorer, I saw lots of threads repeatedly calling CreateApplicationContext. I've tried installing .Net 2.0 SP1, according to some posts I found on the net, but it didn't solve the problem and replaced the function calls with CLRCreateManagedInstance. I'm about to capture a dump using adplus and windbg of the IIS processes and try to figure out what's wrong. Has anyone encountered something like this or has an idea which directory I should check ? p.s. The same version of the application is deployed in another customer, and there it works just fine. I also tried rolling back versions (even very old versions) and it still behaves exactly the same. Edit: well, problem solved, turns out I've had an SQL query in there that didn't limit the result set, and when the customer went over a certain number of rows, it started bogging down the server. Took me two days to find it, because of all the surrounding noise in the logs, but I waited for the night and took a dump then, which immediately showed me the query.

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• Connecting an overloaded PyQT signal using new-style syntax

  - by Claudio

  I am designing a custom widget which is basically a QGroupBox holding a configurable number of QCheckBox buttons, where each one of them should control a particular bit in a bitmask represented by a QBitArray. In order to do that, I added the QCheckBox instances to a QButtonGroup, with each button given an integer ID: def populate(self, num_bits, parent = None): """ Adds check boxes to the GroupBox according to the bitmask size """ self.bitArray.resize(num_bits) layout = QHBoxLayout() for i in range(num_bits): cb = QCheckBox() cb.setText(QString.number(i)) self.buttonGroup.addButton(cb, i) layout.addWidget(cb) self.setLayout(layout) Then, each time a user would click on a checkbox contained in self.buttonGroup, I'd like self.bitArray to be notified so I can set/unset the corresponding bit in the array. For that I intended to connect QButtonGroup's buttonClicked(int) signal to QBitArray's toggleBit(int) method and, to be as pythonic as possible, I wanted to use new-style signals syntax, so I tried this: self.buttonGroup.buttonClicked.connect(self.bitArray.toggleBit) The problem is that buttonClicked is an overloaded signal, so there is also the buttonClicked(QAbstractButton*) signature. In fact, when the program is executing I get this error when I click a check box: The debugged program raised the exception unhandled TypeError "QBitArray.toggleBit(int): argument 1 has unexpected type 'QCheckBox'" which clearly shows the toggleBit method received the buttonClicked(QAbstractButton*) signal instead of the buttonClicked(int) one. So, the question is, how can we specify, using new-style syntax, that self.buttonGroup emits the buttonClicked(int) signal instead of the default overload - buttonClicked(QAbstractButton*)?

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• Liskov Substition and Composition

  - by FlySwat

  Let say I have a class like this: public sealed class Foo { public void Bar { // Do Bar Stuff } } And I want to extend it to add something beyond what an extension method could do....My only option is composition: public class SuperFoo { private Foo _internalFoo; public SuperFoo() { _internalFoo = new Foo(); } public void Bar() { _internalFoo.Bar(); } public void Baz() { // Do Baz Stuff } } While this works, it is a lot of work...however I still run into a problem: public void AcceptsAFoo(Foo a) I can pass in a Foo here, but not a super Foo, because C# has no idea that SuperFoo truly does qualify in the Liskov Substitution sense...This means that my extended class via composition is of very limited use. So, the only way to fix it is to hope that the original API designers left an interface laying around: public interface IFoo { public Bar(); } public sealed class Foo : IFoo { // etc } Now, I can implement IFoo on SuperFoo (Which since SuperFoo already implements Foo, is just a matter of changing the signature). public class SuperFoo : IFoo And in the perfect world, the methods that consume Foo would consume IFoo's: public void AcceptsAFoo(IFoo a) Now, C# understands the relationship between SuperFoo and Foo due to the common interface and all is well. The big problem is that .NET seals lots of classes that would occasionally be nice to extend, and they don't usually implement a common interface, so API methods that take a Foo would not accept a SuperFoo and you can't add an overload. So, for all the composition fans out there....How do you get around this limitation? The only thing I can think of is to expose the internal Foo publicly, so that you can pass it on occasion, but that seems messy.

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• How can I shared controller logic in ASP.NET MVC for 2 controllers, where they are overriden

  - by AbeP

  Hello, I am trying to implement user-friendly URLS, while keeping the existing routes, and was able to do so using the ActionName tag on top of my controller (http://stackoverflow.com/questions/436866/can-you-overload-controller-methods-in-asp-net-mvc) I have 2 controllers: ActionName("UserFriendlyProjectIndex")] public ActionResult Index(string projectName) { ... } public ActionResult Index(long id) { ... } Basically, what I am trying to do is I store the user-friendly URL in the database for each project. If the user enters the URL /Project/TopSecretProject/, the action UserFriendlyProjectIndex gets called. I do a database lookup and if everything checks out, I want to apply the exact same logic that is used in the Index action. I am basically trying to avoid writing duplicate code. I know I can separate the common logic into another method, but I wanted to see if there is a built-in way of doing this in ASP.NET MVC. Any suggestions? I tried the following and I go the View could not be found error message: [ActionName("UserFriendlyProjectIndex")] public ActionResult Index(string projectName) { var filteredProjectName = projectName.EscapeString().Trim(); if (string.IsNullOrEmpty(filteredProjectName)) return RedirectToAction("PageNotFound", "Error"); using (var db = new PIMPEntities()) { var project = db.Project.Where(p => p.UserFriendlyUrl == filteredProjectName).FirstOrDefault(); if (project == null) return RedirectToAction("PageNotFound", "Error"); return View(Index(project.ProjectId)); } } Here's the error message: The view 'UserFriendlyProjectIndex' or its master could not be found. The following locations were searched: ~/Views/Project/UserFriendlyProjectIndex.aspx ~/Views/Project/UserFriendlyProjectIndex.ascx ~/Views/Shared/UserFriendlyProjectIndex.aspx ~/Views/Shared/UserFriendlyProjectIndex.ascx Project\UserFriendlyProjectIndex.spark Shared\UserFriendlyProjectIndex.spark I am using the SparkViewEngine as the view engine and LINQ-to-Entities, if that helps. thank you!

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• Is Accessing USB from web application for cross browser cross os possible at all ?

  - by Ved

  Hey Guys, I am wondering if there is anyway we can achieve this. I heard different things about Silverlight 4 , Java Script or Active X control but not seen any demo of code for any of them. Does anyone know any web component that is available or how to write one. We really like capture client's USB drive via Web and read/write data on it. This has to work for ANY Operating system in Any web browser. Thanks UPDATED What about WPF in browser mode...I read that I can host my wpf apps inside browser and sort of like smart client. Here is a great example of doing this via silverlight 4 but author mentions about possibility of accessing USB on MAC via 1) Enable executing AppleScripts. This option will let us have the same amount of control on a mac machine as we do on a windows machine. 2) Add an overload to ComAutomationFactory.CreateObject() that calls the “Tell Application” command under the scenes and gets a AppleScript object. This option would work extremely well for Office automation. For any other operating system feature, you’ll have to code OS access twice.  I did not quite understand it. Has any tried this ?

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• Does C# allow method overloading, PHP style (__call)?

  - by mr.b

  In PHP, there is a special method named __call($calledMethodName, $arguments), which allows class to catch calls to non-existing methods, and do something about it. Since most of classic languages are strongly typed, compiler won't allow calling a method that does not exist, I'm clear with that part. What I want to accomplish (and I figured this is how I would do it in PHP, but C# is something else) is to proxy calls to a class methods and log each of these calls. Right now, I have code similar to this: class ProxyClass { static logger; public AnotherClass inner { get; private set; } public ProxyClass() { inner = new AnotherClass(); } } class AnotherClass { public void A() {} public void B() {} public void C() {} // ... } // meanwhile, in happyCodeLandia... ProxyClass pc = new ProxyClass(); pc.inner.A(); pc.inner.B(); // ... So, how can I proxy calls to an object instance in extensible way? Extensible, meaning that I don't have to modify ProxyClass whenever AnotherClass changes. In my case, AnotherClass can have any number of methods, so it wouldn't be appropriate to overload or wrap all methods to add logging. I am aware that this might not be the best approach for this kind of problem, so if anyone has idea what approach to use, shoot. Thanks!

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• Comparing all properties of an object using expression trees

  - by stringargs

  Hi, I'm trying to write a simple generator that uses an expression tree to dynamically generate a method that compares all properties of an instance of a type to the properties of another instance of that type. This works fine for most properties, like int an string, but fails for DateTime? (and presumably other nullable value types). The method: static Delegate GenerateComparer(Type type) { var left = Expression.Parameter(type, "left"); var right = Expression.Parameter(type, "right"); Expression result = null; foreach (var p in type.GetProperties()) { var leftProperty = Expression.Property(left, p.Name); var rightProperty = Expression.Property(right, p.Name); var equals = p.PropertyType.GetMethod("Equals", new[] { p.PropertyType }); var callEqualsOnLeft = Expression.Call(leftProperty, equals, rightProperty); result = result != null ? (Expression)Expression.And(result, callEqualsOnLeft) : (Expression)callEqualsOnLeft; } var method = Expression.Lambda(result, left, right).Compile(); return method; } On a DateTime? property it fails with: Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for parameter of type 'System.Object' of method 'Boolean Equals(System.Object)' OK, so it finds an overload of Equals that expects object. So why can't I pass a DateTime? into that, as it's convertible to object? If I look at Nullable<T>, it indeed has an override of Equals(object o). PS: I realize that this isn't a proper generator yet as it can't deal with null values, but I'll get to that :)

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• C# class can not disguise to be another class because GetType method cannot be override

  - by zinking

  there is a statement in the CLR via C# saying in C#, one class cannot disguise to be another, because GetType is virutal and thus it cannot be override but I think in C# we can still hide the parent implementation of GetType. I must missed something if I hide the base GetType implementation then I can disguise my class to be another class, is that correct? The key here is not whether GetType is virutal or not, the question is can we disguise one class to be another in C# Following is the NO.4 answer from the possible duplicate, so My question is more on this. is this kind of disguise possible, if so, how can we say that we can prevent class type disguise in C# ? regardless of the GetType is virtual or not While its true that you cannot override the object.GetType() method, you can use "new" to overload it completely, thereby spoofing another known type. This is interesting, however, I haven't figured out how to create an instance of the "Type" object from scratch, so the example below pretends to be another type. public class NotAString { private string m_RealString = string.Empty; public new Type GetType() { return m_RealString.GetType(); } } After creating an instance of this, (new NotAString()).GetType(), will indeed return the type for a string. share|edit|flag answered Mar 15 at 18:39 Dr Snooze 213 By almost anything that looks at GetType has an instance of object, or at the very least some base type that they control or can reason about. If you already have an instance of the most derived type then there is no need to call GetType on it. The point is as long as someone uses GetType on an object they can be sure it's the system's implementation, not any other custom definition. – Servy Mar 15 at 18:54 add comment

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• How to change the meaning of pointer access operator

  - by kumar_m_kiran

  Hi All, This may be very obvious question, pardon me if so. I have below code snippet out of my project, #include <stdio.h> class X { public: int i; X() : i(0) {}; }; int main(int argc,char *arv[]) { X *ptr = new X[10]; unsigned index = 5; cout<<ptr[index].i<<endl; return 0; } Question Can I change the meaning of the ptr[index] ? Because I need to return the value of ptr[a[index]] where a is an array for subindexing. I do not want to modify existing source code. Any new function added which can change the behavior is needed. Since the access to index operator is in too many places (536 to be precise) in my code, and has complex formulas inside the index subscript operator, I am not inclined to change the code in many locations. PS : 1. I tried operator overload and came to conclusion that it is not possible. 2. Also p[i] will be transformed into *(p+i). I cannot redefine the basic operator '+'. So just want to reconfirm my understanding and if there are any possible short-cuts to achieve. Else I need fix it by royal method of changing every line of code :) .

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• How to Implement an Interface that Requires Duplicate Member Names?

  - by Will Marcouiller

  I often have to implement some interfaces such as IEnumerable<T> in my code. Each time, when implementing automatically, I encounter the following: public IEnumerator<T> GetEnumerator() { // Code here... } public IEnumerator GetEnumerator1() { // Code here... } Though I have to implement both GetEnumerator() methods, they impossibly can have the same name, even if we understand that they do the same, somehow. The compiler can't treat them as one being the overload of the other, because only the return type differs. When doing so, I manage to set the GetEnumerator1() accessor to private. This way, the compiler doesn't complaint about not implementing the interface member, and I simply throw a NotImplementedException within the method's body. However, I wonder whether it is a good practice, or if I shall proceed differently, as perhaps a method alias or something like so. What is the best approach while implementing an interface such as IEnumerable<T> that requires the implementation of two different methods with the same name? EDIT #1 Does VB.NET reacts differently from C# while implementing interfaces, since in VB.NET it is explicitly implemented, thus forcing the GetEnumerator1(). Here's the code: Public Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of T) Implements System.Collections.Generic.IEnumerable(Of T).GetEnumerator // Code here... End Function Public Function GetEnumerator1() As System.Collections.Generic.IEnumerator Implements System.Collections.Generic.IEnumerable.GetEnumerator // Code here... End Function Both GetEnumerator() methods are explicitly implemented, and the compile will refuse them to have the same name. Why?

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• Code Contracts: Do we have to specify Contract.Requires(...) statements redundantly in delegating me

  - by herzmeister der welten

  I'm intending to use the new .NET 4 Code Contracts feature for future development. This made me wonder if we have to specify equivalent Contract.Requires(...) statements redundantly in a chain of methods. I think a code example is worth a thousand words: public bool CrushGodzilla(string weapon, int velocity) { Contract.Requires(weapon != null); // long code return false; } public bool CrushGodzilla(string weapon) { Contract.Requires(weapon != null); // specify contract requirement here // as well??? return this.CrushGodzilla(weapon, int.MaxValue); } For runtime checking it doesn't matter much, as we will eventually always hit the requirement check, and we will get an error if it fails. However, is it considered bad practice when we don't specify the contract requirement here in the second overload again? Also, there will be the feature of compile time checking, and possibly also design time checking of code contracts. It seems it's not yet available for C# in Visual Studio 2010, but I think there are some languages like Spec# that already do. These engines will probably give us hints when we write code to call such a method and our argument currently can or will be null. So I wonder if these engines will always analyze a call stack until they find a method with a contract that is currently not satisfied? Furthermore, here I learned about the difference between Contract.Requires(...) and Contract.Assume(...). I suppose that difference is also to consider in the context of this question then?

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• Creating a web application that can be extended by plugins/modules

  - by Adam Pope

  I'm currently involved with developing a C# CMS-like web application which will be used to standardise our development of websites. From the outset, the idea has been to keep the core as simple as possible to avoid the complexity and menu/option overload that blights many CMS systems. This simple core is now complete and working very well. We envisisaged that the system would be able to accept plugins or modules which would extend the core functionality to suit a given projects needs. These would also be re-usable across projects. For example, a basic catalogue and shopping basket might be needed. All the code for such extensions should be in seperate assemblies. They should be able to provide their own admin interfaces and front-end code from this library. The system should search for available plugins and give the admin user the option to enable/disable the feature. (This is all very much like WordPress plugins) It is crucial that we attack this problem in the correct way, so I'm trying to perform as much due dilligence as possible before jumping in. I am aware of the Plugin Pattern (http://msdn.microsoft.com/en-us/library/ms972962.aspx) and have read some articles on it's use. It seems reasonable but I'm not convinced it's necessarily the correct/best technique for this situation. It seems more suited to processing applications (image/audio manipulation, maths etc). Are there any other options for achieving this kind of UI extensibility functionality? Or is the plugin pattern the way to go? I'd also be interested if anybody has links to articles that explain using the plugin pattern for this purpose?

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• Simplest way to mix sequences of types with iostreams?

  - by Kylotan

  I have a function void write<typename T>(const T&) which is implemented in terms of writing the T object to an ostream, and a matching function T read<typename T>() that reads a T from an istream. I am basically using iostreams as a plain text serialisation format, which obviously works fine for most built-in types, although I'm not sure how to effectively handle std::strings just yet. I'd like to be able to write out a sequence of objects too, eg void write<typename T>(const std::vector<T>&) or an iterator based equivalent (although in practice, it would always be used with a vector). However, while writing an overload that iterates over the elements and writes them out is easy enough to do, this doesn't add enough information to allow the matching read operation to know how each element is delimited, which is essentially the same problem that I have with a single std::string. Is there a single approach that can work for all basic types and std::string? Or perhaps I can get away with 2 overloads, one for numerical types, and one for strings? (Either using different delimiters or the string using a delimiter escaping mechanism, perhaps.)

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• Compiler turning a string& into a basic_string<>&

  - by Shtong

  Hello I'm coming back to C++ after long years spent on other technologies and i'm stuck on some weird behavior when calling some methods taking std::string as parameters : An example of call : LocalNodeConfiguration *LocalNodeConfiguration::ReadFromFile(std::string & path) { // ... throw configuration_file_error(string("Configuration file empty"), path); // ... } When I compile I get this (I cropped file names for readability) : /usr/bin/g++ -g -I/home/shtong/Dev/OmegaNoc/build -I/usr/share/include/boost-1.41.0 -o CMakeFiles/OmegaNocInternals.dir/configuration/localNodeConfiguration.cxx.o -c /home/shtong/Dev/OmegaNoc/source/configuration/localNodeConfiguration.cxx .../localNodeConfiguration.cxx: In static member function ‘static OmegaNoc::LocalNodeConfiguration* OmegaNoc::LocalNodeConfiguration::ReadFromFile(std::string&)’: .../localNodeConfiguration.cxx:72: error: no matching function for call to ‘OmegaNoc::configuration_file_error::configuration_file_error(std::string, std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)’ .../configurationManager.hxx:25: note: candidates are: OmegaNoc::configuration_file_error::configuration_file_error(std::string&, std::string&) .../configurationManager.hxx:22: note: OmegaNoc::configuration_file_error::configuration_file_error(const OmegaNoc::configuration_file_error&) So as I understand it, the compiler is considering that my path parameter turned into a basic_string at some point, thus not finding the constructor overload I want to use. But I don't really get why this transformation happened. Some search on the net suggested me to use g++ but I was already using it. So any other advice would be appreciated :) Thanks

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• When should I implement globalization and localization in C#?

  - by Geo Ego

  I am cleaning up some code in a C# app that I wrote and really trying to focus on best practices and coding style. As such, I am running my assembly through FXCop and trying to research each message it gives me to decide what should and shouldn't be changed. What I am currently focusing on are locale settings. For instance, the two errors that I have currently are that I should be specifying the IFormatProvider parameter for Convert.ToString(int), and setting the Dataset and Datatable locale. This is something that I've never done, and never put much thought into. I've always just left that overload out. The current app that I am working on is an internal app for a small company that will very likely never need to run in another country. As such, it is my opinion that I do not need to set these at all. On the other hand, doing so would not be such a big deal, but it seems like it is unneccessary and could hinder readability to a degree. I understand that Microsoft's contention is to use it if it's there, period. Well, I'm technically supposed to call Dispose() on every object that implements IDisposable, but I don't bother doing that with Datasets and Datatables, so I wonder what the practice is "in the wild."

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• What is the rationale to not allow overloading of C++ conversions operator with non-member function

  - by Vicente Botet Escriba

  C++0x has added explicit conversion operators, but they must always be defined as members of the Source class. The same applies to the assignment operator, it must be defined on the Target class. When the Source and Target classes of the needed conversion are independent of each other, neither the Source can define a conversion operator, neither the Target can define a constructor from a Source. Usually we get it by defining a specific function such as Target ConvertToTarget(Source& v); If C++0x allowed to overload conversion operator by non member functions we could for example define the conversion implicitly or explicitly between unrelated types. template < typename To, typename From > operator To(const From& val); For example we could specialize the conversion from chrono::time_point to posix_time::ptime as follows template < class Clock, class Duration> operator boost::posix_time::ptime( const boost::chrono::time_point<Clock, Duration>& from) { using namespace boost; typedef chrono::time_point<Clock, Duration> time_point_t; typedef chrono::nanoseconds duration_t; typedef duration_t::rep rep_t; rep_t d = chrono::duration_cast<duration_t>( from.time_since_epoch()).count(); rep_t sec = d/1000000000; rep_t nsec = d%1000000000; return posix_time::from_time_t(0)+ posix_time::seconds(static_cast<long>(sec))+ posix_time::nanoseconds(nsec); } And use the conversion as any other conversion. For a more complete description of the problem, see here or on my Boost.Conversion library.. So the question is: What is the rationale to non allow overloading of C++ conversions operator with non-member functions?

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• Argument type deduction, references and rvalues

  - by uj2

  Consider the situation where a function template needs to forward an argument while keeping it's lvalue-ness in case it's a non-const lvalue, but is itself agnostic to what the argument actually is, as in: template <typename T> void target(T&) { cout << "non-const lvalue"; } template <typename T> void target(const T&) { cout << "const lvalue or rvalue"; } template <typename T> void forward(T& x) { target(x); } When x is an rvalue, instead of T being deduced to a constant type, it gives an error: int x = 0; const int y = 0; forward(x); // T = int forward(y); // T = const int forward(0); // Hopefully, T = const int, but actually an error forward<const int>(0); // Works, T = const int It seems that for forward to handle rvalues (without calling for explicit template arguments) there needs to be an forward(const T&) overload, even though it's body would be an exact duplicate. Is there any way to avoid this duplication?

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