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  • C++ traits question

    - by duli
    I have a templated class template <typename Data> class C { ..... } In most situations, I depend on the compiler to let me substitute types for Data. I call methods foo(), goo() on objects of type Data, so what I substitute needs to provide that. I now need to substitute int and string for my Data type. I do not want to specialize because the class is already too big and would require specializing each method (with only small code change). My options (please tell me if there are more) 1) I can provide wrapper classes around int and string which implement the methods foo(), goo() etc 2) provide a traits class traits that calls foo() or goo() on objects of classes that provide foo(),goo() (these are my present substitutable classes) and specialize these classes for int and string. Questions 1) what are the relative merits of 1 vs 2? 2) My traits classes will have static methods. Can a traits class have non-static methods as well? I see most traits classes define constants in the STL. 3) Do I make the traits classes global or should I pass them in as a template parameter for class C?

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  • Why is Attributes.IsDefined() missing overloads?

    - by Hans Passant
    Inspired by an SO question. The Attribute class has several overloads for the IsDefined() method. Covered are attributes applied to Assembly, Module, MemberInfo, ParameterInfo. The MemberInfo overload covers PropertyInfo, FieldInfo, EventInfo, MethodInfo, ConstructorInfo. That takes care of most of the AttributeTargets. Except for one biggy: there is no overload for Attribute.IsDefined(Type, Type) so that you could check if an attribute is defined on a class. Or a struct, delegate or enum for that matter. Not that this is a real problem, Type.GetCustomAttributes() can fix that. But all of the BlahInfo types have this too. I wonder at the lack of symmetry. I can't put a finger on why this would be problem for Type. Guessing at an inheritance problem doesn't explain it to me. Having ValueType in the mix might be a lead, still doesn't make sense. I don't buy "they forgot", they never do. Why is this overload missing?

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  • Is there command-line tool to extract typedef, structure, enumeration, variable, function from a C or C++ file?

    - by FooF
    I am desiring a command-line tool to extract a definition or declaration (typedef, structure, enumeration, variable, or function) from a C or C++ source file. Also a way to replace an existing definition/declaration would be handy (after transforming the extracted definition by a user-submitted script). Is there such generic tool available, or is some resonably close approximation of such a tool? Scriptability and ability to hook-up with user created scripts or programs is of importance here, although I am academically curious of GUI programs too. Open source solutions for Unix/Linux camp are preferred (although I am curious of Windows and OS X tools too). Primary language interests are C and C++ but more generic solution would be even better (I think we do not need super accurate parsing capabilities for finding, extracting and replacing a definition in a program source file). Sample Use Cases (extra - for the curious mind): Given deeply nested structs and variable (array) initializations of these types, suppose there is a need to change a struct definition by adding or reordering fields or rewriting the variable/array definitions in more readable format without introducing errors resulting from manual labor. This would work by extracting the old initializations, then using a script/program to write the new initializations to replace the old ones. For implementing a code browsing tool - extract a definition. Decorative code generation (e.g. logging function entries / returns). Scripted code structuring (e.g. extract this and that thing and put in different place without change - version control commit comment could document the command to perform this operation to make it evident and verifiable that nothing changed). Note about tags: More accurate tag than code-generation would be code-transformation but it does not exist.

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  • Using "as bool?" instead of "object something = ViewState["hi"]"

    - by Programmin Tool
    So I'm going through old code (2.0) and I came across this: object isReviewingValue = ViewState["IsReviewing"]; if (isReviewingValue is bool) { return (bool)isReviewingValue; } My first thought was to us the "as" keyword to avoid the unneeded (bool)isReviewingValue; But "as" only works with non value types. No problem, I just went ahead and did this: bool? isReviewingValue= ViewState["IsReviewing"] as bool?; if (isReviewingValue.HasValue) { return isReviewingValue.Value; } Question is: Besides looking a bit more readable, is this in fact better? EDIT: So this is getting more interesting. I decided to test it using a simple stopwatch and turns out that the second is much faster... Which after reading some of the responses here I didn't expect at all. I was thinking for sure my way was much slower. Tell me what I did wrong: public Stopwatch AsRun() { Stopwatch watch = new Stopwatch(); watch.Start(); for (Int32 loopCounter = 0; loopCounter < 10000; loopCounter++) { Boolean? test = true as Boolean?; if (test.HasValue) { Boolean something = test.Value; } } watch.Stop(); return watch; } public Stopwatch ObjectIsRun() { Stopwatch watch = new Stopwatch(); watch.Start(); for (Int32 loopCounter = 0; loopCounter < 10000; loopCounter++) { Object test = true; if (test is Boolean) { Boolean something = (Boolean)test; } } watch.Stop(); return watch; } Every time I run these methods against each other, the AsRun is twice as fast.

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  • Is there any way to output the actual array in c++

    - by user2511129
    So, I'm beginning C++, with a semi-adequate background of python. In python, you make a list/array like this: x = [1, 2, 3, 4, 5, 6, 7, 8, 9] Then, to print the list, with the square brackets included, all you do is: print x That would display this: [1, 2, 3, 4, 5, 6, 7, 8, 9] How would I do the exact same thing in c++, print the brackets and the elements, in an elegant/clean fashion? NOTE I don't want just the elements of the array, I want the whole array, like this: {1, 2, 3, 4, 5, 6, 7, 8, 9} When I use this code to try to print the array, this happens: input: #include <iostream> using namespace std; int main() { int anArray[9] = {1, 2, 3, 4, 5, 6, 7, 8, 9}; cout << anArray << endl; } The output is where in memory the array is stored in (I think this is so, correct me if I'm wrong): 0x28fedc As a sidenote, I don't know how to create an array with many different data types, such as integers, strings, and so on, so if someone can enlighten me, that'd be great! Thanks for answering my painstakingly obvious/noobish questions!

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  • What to set the scalar type to contain a byte []. Entity in MVC2

    - by Brad8118
    I'm trying out the EF 4.0 and using the Model first approach. I'd like to store images into the database and I'm not sure of the best type for the scalar in the entity. I currently have it(the image scalar type) setup as a binary. From what I have been reading the best way to store the image in the db is a byte[]. So I'm assuming that binary is the way to go. If there is a better way I'd switch. In my controller I have: //file from client to store in the db HttpPostedFileBase file = Request.Files[inputTagName]; if (file.ContentLength > 0) { keyToAdd.Image = new byte[file.ContentLength]; file.InputStream.Write(keyToAdd.Image, 0, file.ContentLength); } This builds fine but when I run it I get an exception writing the stream to keyToAdd.Image. The exception is something like: Method does not exist. Any ideas? Note that when using a EF 4.0 model first approach I only have int16, int32, double, string, decimal, binary, byte, DateTime, Double, Single, and SByte as available types. Thanks

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  • Using MPI_Type_Vector and MPI_Gather, in C.

    - by Goloneg
    Hi, I am trying to multiply square matrices in parallele with MPI. I use a MPI_Type_vector to send square submatrixes (arrays of float) to the processes, so they can calculate subproducts. Then, for the next iterations, these submatrices are send to neighbours processes as MPI_Type_contiguous (the whole submatrix is sent). This part is working as expected, and local results are corrects. Then, I use MPI_Gather with the contiguous types to send all local results back to the root process. The problem is, the final matrix is build (obviously, by this method) line by line instead of submatrix by submatrix. I wrote an ugly procedure rearranging the final matrix, but I would like to know if there is a direct way of performing the "inverse" operation of sending MPI_Type_vectors (i.e., sending an array of values and directly arranging it in a subarray form in the receiving array). An example, to try and clarify my long text : A[16] and B[16] are 4x4 matrices to be multiplied ; C[16] will contain the result ; 4 processes are used (Pi with i from 0 to 3) : Pi gets two 2x2 submatrices : subAi[4] and subBi[4] ; their product is stored locally in subCi[4]. For instance, P0 gets : subA0[4] containing A[0], A[1], A[4] and A[5] ; subB0[4] containing B[0], B[1], B[4] and B[5]. After everything is calculed, root process gathers all subCi[4]. Then C[16] contains : [ subC0[0], subC0[1], subC0[2], subC0[3], subC1[0], subC1[1], subC1[2], subC1[3], subC2[0], subC2[1], subC2[2], subC2[3], subC3[0], subC3[1], subC3[2], subC3[3]] and I would like it to be : [ subC0[0], subC0[1], subC1[0], subC1[1], subC0[2], subC0[3], subC1[2], subC1[3], subC2[0], subC2[1], subC3[0], subC3[1], subC2[2], subC2[3], subC3[2], subC3[3]] without further operation. Does someone know a way ? Thanks for your advices.

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  • Vector Usage in MPI(C++)

    - by lsk1985
    I am new to MPI programming,stiil learning , i was successful till creating the Derived data-types by defining the structures . Now i want to include Vector in my structure and want to send the data across the Process. for ex: struct Structure{ //Constructor Structure(): X(nodes),mass(nodes),ac(nodes) { //code to calculate the mass and accelerations } //Destructor Structure() {} //Variables double radius; double volume; vector<double> mass; vector<double> area; //and some other variables //Methods to calculate some physical properties Now using MPI i want to sent the data in the structure across the processes. Is it possible for me to create the MPI_type_struct vectors included and send the data? I tried reading through forums, but i am not able to get the clear picture from the responses given there. Hope i would be able to get a clear idea or approach to send the data PS: i can send the data individually , but its an overhead of sending the data using may MPI_Send/Recieve if we consider the domain very large(say 10000*10000)

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  • (Java) Is there a type of object that can handle anything from primitives to arrays?

    - by Michael
    I'm pretty new to Java, so I'm hoping one of you guys knows how to do this. I'm having the user specify both the type and value of arguments, in any XML-like way, to be passed to methods that are external to my application. Example: javac myAppsName externalJavaClass methodofExternalClass [parameters] Of course, to find the proper method, we have to have the proper parameter types as the method may be overloaded and that's the only way to tell the difference between the different versions. Parameters are currently formatted in this manner: (type)value(/type), e.g. (int)71(/int) (string)This is my string that I'm passing as a parameter!(/string) I parse them, getting the constructor for whatever type is indicated, then execute that constructor by running its method, newInstance(<String value>), loading the new instance into an Object. This works fine and dandy, but as we all know, some methods take arrays, or even multi-dimensional arrays. I could handle the argument formatting like so: (array)(array)(int)0(/int)(int)1(/int)(/array)(array)(int)2(/int)(int)3(/int)(/array)(/array)... or perhaps even better... {{(int)0(/int)(int)1(/int)}{(int)2(/int)(int)3(/int)}}. The question is, how can this be implemented? Do I have to start wrapping everything in an Object[] array so I can handle primitives, etc. as argObj[0], but load an array as I normally would? (Unfortunately, I would have to make it an Object[][] array if I wanted to support two-dimensional arrays. This implementation wouldn't be very pretty.)

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  • Help - use PHP-broswer, or proxy or get_page_contents or include page, or something else ??

    - by userlite
    Hi, I am trying to develop a web application for which I need to capture a specific user-driven event (such as mouse dblclick) occurring on a different-website page loaded through my website. What I want to do is : User visits my website - hosted by me. There, user types in any website URL (e.g.: http://www.example.com) That URL page gets loaded as is. When user double-clicks mouse over any link or image from that page, a popup/side-panel is displayed with content related to that particular image or link. I can do this with a combination of PHP get_page_contents or include-page, and javascript dblclick. However, when user clicks on any link or submits a form, the control goes to that other website, where I cannot show the side-panel. I might be able to handle the links by proxifying them when user clicks on any of them. How do I handle forms submission and other stuff ? I can use a full-featured proxy, but that will be too heavy just for the purpose of capturing the event. My question is that is there a way to write some kind of light PHP script that sits on my website - that loads other websites contents as is, but lets me capture the mouse-dblclick event to show related-content in the side panel . I have already searched the internet, but could not find anything. Any help is really appreciated. Thanks.

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  • Best way to store this data?

    - by Malfist
    I have just been assigned to renovate an old website, and I get to move it from some old archaic system to drupal. The only problem is that it's a real-estate system and a lot of data is stored. Currently all the information is stored in a single table, an id represents the house and then everything else is key/value pairs. There are a possible 243 keys per estate, there are 23840 estates in the system. As you can imagine the system is slow and difficult to query. I don't think a table with 243 rows would be a very good idea, and probably worse than the current situation. I've done some investigating and here's what I've found out: Missing data does not indicate a 0 value, data is merged from two, unique sources/formats. Some guessing is involved. I have no control over the source of the data. There are 4 keys that are common to all estates, all values look like something that is commonly searched for and could be indexed There are 10 keys that are in the [90-100)% range 8 of these are information like who's selling it, and it's address. The other two seem to belong with the below range There are 80 keys that are in the [80-90)% range This range seems to mostly just list room types and how many the house has (e.g. bedrooms_possible, bathrooms, family_room_3rd, etc) This range also includes some minor information like school districts, one or two more pieces of data on the address. The 179 keys that are in the [0-80)% range include all sorts of miscellaneous information about the estate My best idea was a hybrid approach, create a table that stores important, common information and keep a smaller key/value table. How would you store this information?

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  • Displaying Query Results Horizontally

    - by AndyD273
    I am wondering if it is possible to take the results of a query and return them as a CSV string instead of as a column of cells. Basically, we have a table called Customers, and we have a table called CustomerTypeLines, and each Customer can have multiple CustomerTypeLines. When I run a query against it, I run into problems when I want to check multiple types, for instance: Select * from Customers a Inner Join CustomerTypeLines b on a.CustomerID = b.CustomerID where b.CustomerTypeID = 14 and b.CustomerTypeID = 66 ...returns nothing because a customer can't have both on the same line, obviously. In order to make it work, I had to add a field to Customers called CustomerTypes that looks like ,14,66,67, so I can do a Where a.CustomerTypes like '%,14,%' and a.CustomerTypes like '%,66,%' which returns 85 rows. Of course this is a pain because I have to make my program rebuild this field for that Customer each time the CustomerTypeLines table is changed. It would be nice if I could do a sub query in my where that would do the work for me, so instead of returning the results like: 14 66 67 it would return them like ,14,66,67, Is this possible?

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  • Defining implicit and explicit casts for C# interfaces

    - by ehdv
    Is there a way to write interface-based code (i.e. using interfaces rather than classes as the types accepted and passed around) in C# without giving up the use of things like implicit casts? Here's some sample code - there's been a lot removed, but these are the relevant portions. public class Game { public class VariantInfo { public string Language { get; set; } public string Variant { get; set; } } } And in ScrDictionary.cs, we have... public class ScrDictionary: IScrDictionary { public string Language { get; set; } public string Variant { get; set; } public static implicit operator Game.VariantInfo(ScrDictionary s) { return new Game.VariantInfo{Language=sd.Language, Variant=sd.Variant}; } } And the interface... public interface IScrDictionary { string Language { get; set; } string Variant { get; set; } } I want to be able to use IScrDictionary instead of ScrDictionary, but still be able to implicitly convert a ScrDictionary to a Game.VariantInfo. Also, while there may be an easy way to make this work by giving IScrDictionary a property of type Game.VariantInfo my question is more generally: Is there a way to define casts or operator overloading on interfaces? (If not, what is the proper C# way to maintain this functionality without giving up interface-oriented design?)

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  • Acessing elements of this xml

    - by csU
    <wsdl:definitions targetNamespace="http://www.webserviceX.NET/"> <wsdl:types> <s:schema elementFormDefault="qualified" targetNamespace="http://www.webserviceX.NET/"> <s:element name="ConversionRate"> <s:complexType> <s:sequence> <s:element minOccurs="1" maxOccurs="1" name="FromCurrency" type="tns:Currency"/> <s:element minOccurs="1" maxOccurs="1" name="ToCurrency" type="tns:Currency"/> </s:sequence> </s:complexType> </s:element> <s:simpleType name="Currency"> <s:restriction base="s:string"> <s:enumeration value="AFA"/> <s:enumeration value="ALL"/> <s:enumeration value="DZD"/> <s:enumeration value="ARS"/> i am trying to get at all of the elements in enumeration but cant seem to get it right. This is homework so please no full solutions, just guidance if possible. $feed = simplexml_load_file('http://www.webservicex.net/CurrencyConvertor.asmx?WSDL'); foreach($feed->simpleType as $val){ $ns s = $val->children('http://www.webserviceX.NET/'); echo $ns_s -> enumeration; } what am i doing wrong? thanks

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  • Mercurial "server"

    - by user85116
    I've been using mercurial for a little while, but mainly for my own usage. Now though, I have a project I'm working on where two of us are building the same project, and we will probably be modifiying each other's files. I would like to setup a mercurial repo on a server, make that repo the "server", so my changes and the other editor's changes both push to that server (so basically the subversion / cvs model); I like mercurial though, and don't want to switch to something like subversion. Here in my own network, everything is done on linux, and my "server" has openssh installed. So pushing my changes (I work on multiple computers) from one computer to the server is just a matter of "hg push"; the protocol used is ssh for transfering the changes. The problem is that I use linux, the server will be windows (so no openssh, right?) and the other editor will be using windows too. As far as I know, the best way of working in mercurial in these types of setups is for the repo to pull changes from the source, rather then the source pushing to the "server". I'm behind several firewall's (not entirely my network) and my computer won't be visible from the server, and I'm assuming the other editor will be behind a firewall too (so we can't just start up the local mercurial http server and get the "server" computer to pull from that). What's the best way for both editors to get our changes to the server repo? (I should add that the server is a server on the internet, so just as visible as something like google.com. It's a hosted windows server, but I would probably have permission to install software if needed for this)

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  • Designing a database for a user/points system? (in Django)

    - by AP257
    First of all, sorry if this isn't an appropriate question for StackOverflow. I've tried to make it as generalisable as possible. I want to create a database (MySQL, site running Django) that has users, who can be allocated a certain number of points for various types of action - it's a collaborative game. My requirements are to obtain: the number of points a user has the user's ranking compared to all other users and the overall leaderboard (i.e. all users ranked in order of points) This is what I have so far, in my Django models.py file: class SiteUser(models.Model): name = models.CharField(max_length=250 ) email = models.EmailField(max_length=250 ) date_added = models.DateTimeField(auto_now_add=True) def points_total(self): points_added = PointsAdded.objects.filter(user=self) points_total = 0 for point in points_added: points_total += point.points return points_total class PointsAdded(models.Model): user = models.ForeignKey('SiteUser') action = models.ForeignKey('Action') date_added = models.DateTimeField(auto_now_add=True) def points(self): points = Action.objects.filter(action=self.action) return points class Action(models.Model): points = models.IntegerField() action = models.CharField(max_length=36) However it's rapidly becoming clear to me that it's actually quite complex (in Django query terms at least) to figure out the user's ranking and return the leaderboard of users. At least, I'm finding it tough. Is there a more elegant way to do something like this? This question seems to suggest that I shouldn't even have a separate points table - what do people think? It feels more robust to have separate tables, but I don't have much experience of database design.

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  • Usability for notification messages, colors

    - by metrobalderas
    In each app I develop, I like to add three types of messages: Green/blue for success messages Yellow for warnings Red for errors And perhaps, a neutral one for information, which is gray or blue if the success one is green. The success one is used for when an item is created or updated, the yellow one is when there's something wrong, but not we-are-going-to-die wrong and the red one is when something is blocked or we are going to die. However, there's one thing I can't figure out, when I delete an object, what kind of notification should I use? I think the success one is not because it is not expected, altough the deletion was successful, the user tends not to read the message, just to see the color. The red one might be, but it can be misunderstood (I tried to delete it but there was an error), the warning and the information one might be good choices, but I'm not really sure. Also, when you ask for confirmation about deleting something, the 'cancel' button should be green or red? I'm just curious how you guys handle this. Thanks.

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  • guarantee child records either in one table or another, but not both?

    - by user151841
    I have a table with two child tables. For each record in the parent table, I want one and only one record in one of the child tables -- not one in each, not none. How to I define that? Here's the backstory. Feel free to criticize this implementation, but please answer the question above, because this isn't the only time I've encountered it: I have a database that holds data pertaining to user surveys. It was originally designed with one authentication method for starting a survey. Since then, requirements have changed, and now there are two different ways someone could sign on to start a survey. Originally I captured the authentication token in a column in the survey table. Since requirements changed, there are three other bits of data that I want to capture in authentication. So for each record in the survey table, I'm either going to have one token, or a set of three. All four of these are of different types, so my thought was, instead of having four columns where either one is going to be null, or three are going to be null ( or even worse, a bad mashup of either of those scenarios ), I would have two child tables, one for holding the single authentication token, the other for holding the three. Problem is, I don't know offhand how to define that in DDL. I'm using MySQL, so maybe there's a feature that MySQL doesn't implement that lets me do this.

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  • Alternative to Altova's MissionKit

    - by nomad311
    Anyone know of any good alternatives (other than those listed below which really are only good at specific XML development tasks)? The Why (if you're interested): I've been doing XML development on and off for years now, but someone brought XMLSpy to my attention recently, and it is awesome - the price isn't. Lately I've been using a combination of: Notepad++ (modifying XML) EditX (validating/debugging XML) Eclipse (designing schemas) and MS Visual Studio (validating schemas) ...based on which makes the task(s) easiest. But, I've just found out that we will be using XSL transformations to generate XML in the future. I've never used mission kit before, but I'm just short of positive XMLSpy replaces all the above mentioned tool for XML development. And if their XSL tools are anywhere near the caliber of XMLSpy ...simply put I need it. I don't believe that I can convince the budgeting types to buy licenses for MissionKit at $1000 each (won't stop me from trying). In the mean while some research on alternatives won't hurt, but a few Google queries has only revealed that not many people pay for Altova's (overpriced?) software as there are mostly links to P2P sites for downloading a more free-like version of MissionKit.

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  • iPhone SDK File Handler with iOS 4 Background Processes

    - by David Higgins
    The "application:applicationDidFinishLaunchingWithOptions:" message does not get called when an application is sitting in the background in iOS 4, and I'm trying to figure out how to be notified when the application is brought back into the foreground by another application. My application registers itself as a handler for certain file types, and Safari and other supported applications allow passing the files over to my app. This works great if the app is closed before I try to use it, but fails otherwise. In my application:applicationDidFinishLaunchingWithOptions: I have: NSURL *url = (NSURL *)[launchOptions valueForKey:UIApplicationLaunchOptionsURLKey]; if([url isFileURL]) { } [self.window makeKeyAndVisible]; return YES; As stated already, this works great so far for starting the app when it's not sitting in the background - but when I switch back over to Safari or Mail and try to open a new file that is supported, my application wakes up from the background and becomes active again but I can't see any "withOptions" overrides for application:applicationWillEnterForeground: or any way to identify what was passed in when it enters the foreground. What would be the appropriate way to receive these "open file notifications" when the application is in the background?

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  • C++: Conceptual problem in designing an intepreter

    - by sub
    I'm programming an interpreter for an experimental programming language (educational, fun,...) So far, everything went well (Tokenizer & Parser), but I'm getting a huge problem with some of the data structures in the part that actually runs the tokenized and parsed code. My programming language basically has only two types, int and string, and they are represented as C++ strings (std class) and ints Here is a short version of the data structure that I use to pass values around: enum DataType { Null, Int, String } class Symbol { public: string identifier; DataType type; string stringValue; int intValue; } I can't use union because string doesn't allow me to. This structure above is beginning to give me a headache. I have to scatter code like this everywhere in order to make it work, it is beginning to grow unmaintainable: if( mySymbol.type == Int ) { mySymbol.intValue = 1234; } else { mySymbol.stringValue = "abcde"; } I use the Symbol data structure for variables, return values for functions and general representation of values in the programming language. Is there any better way to solve this? I hope so!

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  • Action on each method's return value

    - by RobGlynn
    What I'd like to do is take some action using the value returned by every method in a class. So for instance, if I have a class Order which has a method public Customer GetCustomer() { Customer CustomerInstance = // get customer return CustomerInstance; } Let's say I want to log the creation of these - Log(CustomerInstance); My options (AFAIK) are: Call Log() in each of these methods before returning the object. I'm not a fan of this because it gets unwieldy if used on a lot of classes with a lot of methods. It also is not an intrinsic part of the method's purpose. Use composition or inheritance to layer the log callon the Order class similar to: public Customer GetCustomer() { Customer CustomerInstance = this.originalCustomer.GetCustomer(); Log(CustomerInstance); return CustomerInstance; } I don't think this buys me anything over #1. Create extension methods on each of the returned types: Customer CustomerInstance = Order.GetCustomer().Log(); which has just as many downsides. I'm looking to do this for every (or almost every) object returned, automatically if possible, without having to write double the amount of code. I feel like I'm either trying to bend the language into doing something it's not supposed to, or failing to recognize some language feature that would enable this. Possible solutions would be greatly appreciated.

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  • SQL Server: Why use shorter VARCHAR(n) fields?

    - by chryss
    It is frequently advised to choose database field sizes to be as narrow as possible. I am wondering to what degree this applies to SQL Server 2005 VARCHAR columns: Storing 10-letter English words in a VARCHAR(255) field will not take up more storage than in a VARCHAR(10) field. Are there other reasons to restrict the size of VARCHAR fields to stick as closely as possible to the size of the data? I'm thinking of Performance: Is there an advantage to using a smaller n when selecting, filtering and sorting on the data? Memory, including on the application side (C++)? Style/validation: How important do you consider restricting colunm size to force non-sensical data imports to fail (such as 200-character surnames)? Anything else? Background: I help data integrators with the design of data flows into a database-backed system. They have to use an API that restricts their choice of data types. For character data, only VARCHAR(n) with n <= 255 is available; CHAR, NCHAR, NVARCHAR and TEXT are not. We're trying to lay down some "good practices" rules, and the question has come up if there is a real detriment to using VARCHAR(255) even for data where real maximum sizes will never exceed 30 bytes or so. Typical data volumes for one table are 1-10 Mio records with up to 150 attributes. Query performance (SELECT, with frequently extensive WHERE clauses) and application-side retrieval performance are paramount.

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  • Why can't these generic type parameters be inferred?

    - by Jon M
    Given the following interfaces/classes: public interface IRequest<TResponse> { } public interface IHandler<TRequest, TResponse> where TRequest : IRequest<TResponse> { TResponse Handle(TRequest request); } public class HandlingService { public TResponse Handle<TRequest, TResponse>(TRequest request) where TRequest : IRequest<TResponse> { var handler = container.GetInstance<IHandler<TRequest, TResponse>>(); return handler.Handle(request); } } public class CustomerResponse { public Customer Customer { get; set; } } public class GetCustomerByIdRequest : IRequest<CustomerResponse> { public int CustomerId { get; set; } } Why can't the compiler infer the correct types, if I try and write something like the following: var service = new HandlingService(); var request = new GetCustomerByIdRequest { CustomerId = 1234 }; var response = service.Handle(request); // Shouldn't this know that response is going to be CustomerResponse? I just get the 'type arguments cannot be inferred' message. Is this a limitation with generic type inference in general, or is there a way to make this work?

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  • Overload the behavior of count() when called on certain objects

    - by Tom
    In PHP 5, you can use magic methods, overload some classes, etc. In C++, you can implement functions that exist is STL as long as the argument types are different. Is there a way to do this in PHP? An example of what I'd like to do is this: class a { function a() { $this->list = array("1", "2"); } } $blah = new a(); count($blah); I would like blah to return 2. IE count the values of a specific array in the class. So in C++, the way I would do this might look like this: int count(a varName) { return count(varName->list); } Basically, I am trying to simplify data calls for a large application so I can call do this: count($object); rather than count($object->list); The list is going to be potentially a list of objects so depending on how it's used, it could be really nasty statement if someone has to do it the current way: count($object->list[0]->list[0]->list); So, can I make something similar to this: function count(a $object) { count($object->list); } I know PHP's count accepts a mixed var, so I don't know if I can override an individual type.

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