Search Results

Search found 7324 results on 293 pages for 'operations research'.

Page 249/293 | < Previous Page | 245 246 247 248 249 250 251 252 253 254 255 256  | Next Page >

  • Rails - Dynamic name routes namespace

    - by Kuro
    Hi, Using Rails 2.3, I'm trying to configure my routes but I uncounter some difficulties. I would like to have something like : http:// mydomain.com/mycontroller/myaction/myid That should respond with controllers in :front namespace http:// mydomain.com/aname/mycontroller/myaction/mydi That should respond with controllers in :custom namespace I try something like this, but I'm totaly wrong : map.namespace :front, :path_prefix => "" do |f| f.root :controller => :home, :action => :index f.resources :home ... end map.namespace :custom, :path_prefix => "" do |m| m.root :controller => :home, :action => :index m.resources :home ... m.match ':sub_url/site/:controller/:action/:id' m.match ':sub_url/site/:controller/:action/:id' m.match ':sub_url/site/:controller/:action/:id.:format' m.match ':sub_url/site/:controller/:action.:format' end I put matching instruction in custom namespace but I'm not sure it's the right place for it. I think I really don't get the way to customize fields in url matching and I don't know how to find documentation about Rails 2.3, most of my research drove me to Rails 3 doc about the topic... Somebody to help me ?

    Read the article

  • Question about architecting asp.net mvc application ?

    - by Misnomer
    I have read little bit about architecture and also patterns in order to follow the best practices. So this is the architecture we have and I wanted to know what you think of it and any proposed changes or improvements to it - Presentation Layer - Contains all the views,controllers and any helper classes that the view requires also it containes the reference to Model Layer and Business Layer. Business Project - Contains all the business logic and validation and security helper classes that are being used by it. It contains a reference to DataAccess Layer and Model Layer. Data Access Layer - Contains the actual queries being made on the entity classes(CRUD) operations on the entity classes. It contains reference to Model Layer. Model Layer - Contains the entity framework model,DTOs,Enums.Does not really have a reference to any of the above layers. What are your thoughts on the above architecture ? The problem is that I am getting confused by reading about like say the repository pattern, domain driven design and other design patterns. The architecture we have although not that strict still is relatively alright I think and does not really muddle things but I maybe wrong. I would appreciate any help or suggestions here. Thanks !

    Read the article

  • Automatically Organize Tags in Tax/Folksonomy

    - by Rob Wilkerson
    I'm working on a process that will perform natural language processing (NLP) on one--and potentially several--of our content rich sites. What I'd like to do once the NLP is complete is to automatically organize the output (generally a set of terms that you might think of as tags given the prevalence of that metaphor) into some kind of standard or generally accepted organizational structure. In a perfect world, I'd really like this to be crowd sourced under the folksonomy concept (as opposed to a taxonomy) since the ultimate goal is to target/appeal to real people rather than "domain experts", but I'm open to ideas and best practices. For the obvious purpose of scalability, I'd like to automate the population of this tax/folksonomy so that "some guy" in the team/organization isn't responsible for looking at a bunch of words (with or without context) and arbitrarily fleshing out the contextual components of the tree. I have a few ideas for doing this that require some research to establish viability, but I have exactly zero practical experience with this sort of thing so the ideas really just boil down to stuff I made up that might perform some role in accomplishing the task. Imagining that others have vastly more experience with this sort of thing, I'm hoping that I can stand on your shoulders. Thanks for your thoughts and insights.

    Read the article

  • Solving problems with near infinite potential solutions

    - by Zonda333
    Today I read the following problem: Use the digits 2, 0, 1, 1 and the operations +, -, x, ÷, sqrt, ^ , !, (), combinations, and permutations to write equations for the counting numbers 1 through 100. All four digits must be used in each expression. Only the digits 2, 0, 1, 1 may be used, and each must be used exactly once. Decimals may be used, as in .1, .02, etc. Digits may be combined; numbers such as 20 or 101 may be used. Example: 60 = 10*(2+1)!, 54 = ¹¹C2 - 0! Though I was able to quickly find around 50 solutions quite easily in my head, I thought programming it would be a far superior solution. However, I then realized I had no clue how to go about solving a problem like this. I am not asking for complete code for me to copy and paste, but for ideas about how I would solve this problems, and others like it that have nearly infinite potential solutions. As I will be writing it in python, where I have the most experience, I would prefer if the answers were more python based, but general ideas are great too.

    Read the article

  • How to parse mathematical expressions involving parentheses

    - by Rob P.
    Please forgive my title, I really don't know how to phrase it better. This isn't a school assignment or anything, but I realize it's a mostly academic question. But, what I've been struggling to do is parse 'math' text and come up with an answer. For Example - I can figure out how to parse '5 + 5' or '3 * 5' - but I fail when I try to correctly chain operations together. (5 + 5) * 3 It's mostly just bugging me that I can't figure it out. If anyone can point me in a direction, I'd really appreciate it. EDIT Thanks for all of the quick responses. I'm sorry I didn't do a better job of explaining. First - I'm not using regular expressions. I also know there are already libraries available that will take, as a string, a mathematical expression and return the correct value. So, I'm mostly looking at this because, sadly, I don't "get it". Second - What I've tried doing (is probably misguided) but I was counting '(' and ')' and evaluating the deepest items first. In simple examples, this worked; but my code is not pretty and more complicated stuff crashes. When I 'calculated' the lowest level, I was modifying the string. So... (5 + 5) * 3 Would turn into 10 * 3 Which would then evaluate to 30 But it just felt 'wrong'. I hope that helps clarify things. I'll certainly check out the links provided.

    Read the article

  • Writing own Unix shell in C - Problems with PATH and execv

    - by user1287523
    I'm writing my own shell in C. It needs to be able to display the users current directory, execute commands based on the full path (must use execv), and allow the user to change the directory with cd. This IS homework. The teacher only gave us a basic primer on C and a very brief skeleton on how the program should work. Since I'm not one to give up easily I've been researching how to do this for three days, but now I'm stumped. This is what I have so far: Displays the user's username, computername, and current directory (defaults to home directory). Prompts the user for input, and gets the input Splits the user's input by " " into an array of arguments Splits the environment variable PATH by ":" into an array of tokens I'm not sure how to proceed from here. I know I've got to use the execv command but in my research on google I haven't really found an example I understand. For instance, if the command is bin/ls, how does execv know the display all files/folders from the home directory? How do I tell the system I changed the directory? I've been using this site a lot which has been helpful: http://linuxgazette.net/111/ramankutty.html but again, I'm stumped. Thanks for your help. Let me know if I should post some of my existing code, I'm wasn't sure if it was necessary though.

    Read the article

  • C/C++ Bit Array or Bit Vector

    - by MovieYoda
    Hi, I am learning C/C++ programming & have encountered the usage of 'Bit arrays' or 'Bit Vectors'. Am not able to understand their purpose? here are my doubts - Are they used as boolean flags? Can one use int arrays instead? (more memory of course, but..) What's this concept of Bit-Masking? If bit-masking is simple bit operations to get an appropriate flag, how do one program for them? is it not difficult to do this operation in head to see what the flag would be, as apposed to decimal numbers? I am looking for applications, so that I can understand better. for Eg - Q. You are given a file containing integers in the range (1 to 1 million). There are some duplicates and hence some numbers are missing. Find the fastest way of finding missing numbers? For the above question, I have read solutions telling me to use bit arrays. How would one store each integer in a bit?

    Read the article

  • Chrome.tabs.getSelected() doesn't work. What am I doing wrong ?

    - by warv3n
    Hi there ! I'm building my first GC extension, and I am having a problem using this function. I would like to get the url of the current tab, and to do so (after some google research, of course), I use the chrome.tabs.getSelected() function. Here it is in my code : ... socket.onopen = function(msg){ log("Welcome - status " + this.readyState); chrome.tabs.getSelected(null, function(tab){ sendUrl(tab.url); }); }; function sendUrl(tabUrl) { socket.send("#URL#"+ tabUrl); } The socket.open is a listener for the Websocket API I use in my extension. The log function print the status of the socket (1, which means it's OPEN or connected and ready to communicate, according to the Websocket API), but the chrome.tabs.getSelected() function do not seems to work, as the server do not receive anything (the socket is not the problem here, I tried to send a test message with socket.send() instead of chrome.tabs.getSelected() and the server received it). I put the permissions: ["tabs"] into the manifest.json so I can use this function. So I don't know what I am doing wrong here ? I also tried to put chrome.tab.getSelected() elsewhere in the code, but it is still not working. Any help is welcome :)

    Read the article

  • Android Facebook RequestListener

    - by Marcus King
    I'm new to Java, but have been a .NET developer for years now and I am a bit confused about the point of the RequestListener object as I can't retrieve the results of my asynchronous calls on the UI thread from what I can tell. My research has told me I should not use singletons or the application context object for getting and storing data. I could use sqlLite, but the data I need is too transient to bother. I would like to know how to have the asyncfacebookrunner object report back it's responses to the UI thread so I can proceed to make decisions between my own api and the objects returned to me from the facebook calls I am making in the async calls. Am I missing something? I can't seem to find a way to get data out. I can pass a Bundle in, but I'm not too sure how to get data out. I would think I would pass it an Intent object to retrieve, but I am not seeing it. I think my eyes are crossed from lack of sleep at this point. Any help here?

    Read the article

  • Can I modify the way Windows draws the Aero UI?

    - by LonelyPixel
    Windows 7 with Aero Glass basically looks quite nice I think. But it has some major drawbacks regarding readability: I cannot easily tell whether a window is currently active or not. I've been tweaking the colours and transparency levels a lot recently but the only safe indicator is the close button: it's red when the window is active, it's colourless otherwise. Then there's the window title text. It is always painted black, on however dark a background. Again, regardless of whether the window is active or not. I've seen WindowBlinds and the tons of available themes you can use with it. Browsing through the most popular or highest rated in several categories I was really scared. I don't want to face Terminator every day, feel like in the Jungle or be fooled that I had an Apple computer which I do not. All I want to change is to make a greater colour difference between active and inactive windows and to invert the window title text colour for dark backgrounds. (Including that visibility hack of a spray brush background.) Is there some Windows API to alter the way Windows draws its windows or does it take the years of private research from Stardock to hook into that? I mean they say it's approved by Microsoft, so I assume there's some official documentation for that, I just couldn't find any.

    Read the article

  • Is Prolog the best language to solve this kind of problem?

    - by Milan Babuškov
    I have this problem containing some inequations and requirement to minimize a value. After doing some research on the Internet, I came to conclusion that using Prolog might be the easiest way to solve it. However, I never used Prolog before, and I would hate to waste my time learning it just to discover that it is not the right tool for this job. Please, if you know Prolog, take a look at this problem and tell me if Prolog is the right one. Or, if you know of some other language that is really suited for this. a + b + c >= 100 d + e + f >= 50 g + h >= 30 if (8b + 2e + 7h > 620) then y = 0.8 else y = 1.0 if (d > 35) then x = 0.9 else x = 1.0 5xa + 8yb + 5c + 3xd + 2ye + 2f + 6xg + 7yh = w. I need to find the values for a, b, c, d, e, f, g and h that minimize w. I'm not really asking for code, although I'd be grateful for some hint how to tackle this if Prolog is really good for it. Thanks.

    Read the article

  • Why is no encoding set in reponse by tomcat? How can I deal with it?

    - by Dishayloo
    I had recently a problem with encoding of websites generated by servlet, that occured if the servlets were deployed under tomcat, but not under jetty. I did a little bit of research about it and simplified the problem to the following servlet: public class TestServlet extends HttpServlet implements Servlet { @Override public void service(HttpServletRequest request, HttpServletResponse response) throws IOException { response.setContentType("text/plain"); Writer output = response.getWriter(); output.write("öäüÖÄÜß"); output.flush(); output.close(); } } If I deploy this under Jetty and direct the browser to it, it returns the expected result. The data is returned as ISO-8859-1 and if I take a look into the headers, then Jetty returns: Content-Type: text/plain; charset=iso-8859-1 The browser detects the encoding from this header. If I deploy the same servlet in a tomcat, the browser shows up strange characters. But Tomcat also returns the data as ISO-8859-1, the difference is, that no header tells about it. So the browser has to guess the encoding, and that goes wrong. My question is, is that behaviour of tomcat correct or a bug? And if it is correct, how can I avoid this problem? Sure, I can always add response.setCharacterEncoding("UTF-8"); to the servlet, but that means I set a fixed encoding, that the browser might or might not understand. The problem is more relevant, if no browser but another service accesses the servlet. So how I should deal with the problem in the most flexible way?

    Read the article

  • Is there any library/software available that can give me useful measurements of image quality?

    - by Thor84no
    I realise measuring image quality in software is going to be really difficult, and I'm not looking for a quick-fix. Googling this is largely showing up research papers and discussions that go a bit over my head, so I was wondering if anyone in the SO community had any experience with doing any rough image quality assessment? I want to use this to scan a few thousand images and whittle it down to a few dozen images that are most likely of poor quality. I could then show these to a user and leave the rest to them. Obviously there are many metrics that can be a part of whether an image is of high/low quality, I'd be happy with anything that could take an image as an input and give some reasonable metrics to any of the basic image quality metrics like sharpness, dynamic range, noise, etc., leaving it up to my software to determine what's acceptable and what isn't. Some of the images are poor quality because they've been up-scaled drastically. If there isn't a way of getting metrics like I suggested above, is there any way to detect that an image has been up-scaled like this?

    Read the article

  • How to implement the API/SPI Pattern in Java?

    - by Adam Tannon
    I am creating a framework that exposes an API for developers to use: public interface MyAPI { public void doSomeStuff(); public int getWidgets(boolean hasRun); } All the developers should have to do is code their projects against these API methods. I also want them to be able to place different "drivers"/"API bindings" on the runtime classpath (the same way JDBC or SLF4J work) and have the API method calls (doSomeStuff(), etc.) operate on different 3rd party resources (files, servers, whatever). Thus the same code and API calls will map to operations on different resources depending on what driver/binding the runtime classpath sees (i.e. myapi-ftp, myapi-ssh, myapi-teleportation). How do I write (and package) an SPI that allows for such runtime binding, and then maps MyAPI calls to the correct (concrete) implementation? In other words, if myapi-ftp allows you to getWidgets(boolean) from an FTP server, how would I could this up (to make use of both the API and SPI)? Bonus points for concrete, working Java code example! Thanks in advance!

    Read the article

  • TCP/IP Implementation General Questions

    - by user2971023
    I've implemented the concepts shown here; http://wiki.unity3d.com/index.php/Simple_TCP/IP_Client_-_Server outside of unity and it works. (though i had to create the TCPIPServerApp from scratch as i could not find the base project anywhere). I have some general questions on how to use tcp/ip properly however. I've done some research on tcp/ip itself but I'm still a little confused. It seems like using the method above doesn't guarantee that I'll see the message (res). It just checks on every update to see if there is a different message in res. What if multiple messages are sent and the program lags or something, will i miss the earlier packet(s)? Should i instead do an array so it stores the last X messages? How do i know the data was received? Do I need to add a message id and build in my own ack into the data? Should i check to see if the port is in use before setting up a connection? Sorry for all the questions. This is all new to me but I enjoy this very much! ... Below already answered By Anton, Thanks It sounds like tcp uses its own packet numbering to ensure the packets end up in the right order on the other side. What if a packet is missed, are the subsequent packets thrown away? Or is this numbering and packet ordering, only for handling data that is broken out into multiple packets? TCP will automatically break the data into multiple packets if necessary right?

    Read the article

  • Data Structure / Hash Function to link Sets of Ints to Value

    - by Gaminic
    Given n integer id's, I wish to link all possible sets of up to k id's to a constant value. What I'm looking for is a way to translate sets (e.g. {1, 5}, {1, 3, 5} and {1, 2, 3, 4, 5, 6, 7}) to unique values. Guarantees: n < 100 and k < 10 (again: set sizes will range in [1, k]). The order of id's doesn't matter: {1, 5} == {5, 1}. All combinations are possible, but some may be excluded. All sets and values are constant and made only once. No deletes or inserts, no value updates. Once generated, the only operations taking place will be look-ups. Look-ups will be frequent and one-directional (given set, look up value). There is no need to sort (or otherwise organize) the values. Additionally, it would be nice (but not obligatory) if "neighboring" sets (drop one id, add one id, swap one id, etc) are easy to reach, as well as "all sets that include at least this set". Any ideas?

    Read the article

  • Pointers into elements in a container

    - by Pillsy
    Say I have an object: struct Foo { int bar_; Foo(int bar) bar_(bar) {} }; and I have an STL container that contains Foos, perhaps a vector, and I take // Elsewhere... vector<Foo> vec; vec.push_back(Foo(4)); int *p = &(vec[0].bar_) This is a terrible idea, right? The reason is that vector is going to be storing its elements in a dynamically allocated array somewhere, and eventually, if you add enough elements, it will have to allocate another array, copy over all the elements of the original array, and delete the old array. After that happens, p points to garbage. This is why many operations on a vector will invalidate iterators. It seems like it would be reasonable to assume that an operation that would invalidate iterators from a container will also invalidate pointers to data members of container elements, and that if an operation doesn't invalidate iterators, those pointers will still be safe. However, many reasonable assumptions are false. Is this one of them?

    Read the article

  • Velocity CTP: can we 'search' for objects?

    - by Stato Machino
    It appears that 'tags' allow us to associate a 'search term' with the objects placed into the Velocity cache space. However, these can only be queried within a 'region'. Further, regions somehow limit the locality of objects in the cache to a single server (or maybe something kinda like that). So this appears to make it hard to perform any operation for which the unique Id of the cached item is not persisted or continuously available to the application that stores and retrieves objects to and from the cache. In any case, I can't see an easy way to 'cleanse' the cache of objects or to find objects across the entire cache that may share some prefix, postfix or infix values in the cache key so that i can clear out the cache of object repeatedly created in unit tests, for example. And I am unsure about the consequences of regions being associated with single server cache locations. So I would appreciate any help with the following questions: What is the difference between a 'distributed cache' (called a 'partitioned' cache??) when using regions, and a 'local cache'? 1.a. In particular, are the region-oriented values in a distributed cache visible through a cache factory that is configured to 'see' the entire cache space? Are the operations of creating and removing 'regions' efficient enough that it would be reasonable to create a region and a group of tags for each bundle of objects that need to be cached? 2.a. Or does this just push the problem of scoping the 'search for objects' up the chain because the ability of the DataCache object to query down through regions and tags as limited as querying for the cache keys of objects themselves. Thanks, Stato

    Read the article

  • Batch Inserts And Prepared Query Error

    - by ircmaxell
    Ok, so I need to populate a MS Access database table with results from a MySQL query. That's not hard at all. I've got the program written to where it copies a template .mdb file to a temp name and opens it via odbc. No problem so far. I've noticed that Access does not support batch inserting (VALUES (foo, bar), (second, query), (third query)). So that means I need to execute one query per row (there are potentially hundreds of thousands of rows). Initial performance tests show a rate of around 900 inserts/sec into Access. With our largest data sets, that could mean execution times of minutes (Which isn't the end of the world, but obviously the faster the better). So, I tried testing a prepared statement. But I keep getting an error (Warning: odbc_execute() [function.odbc-execute]: SQL error: [Microsoft][ODBC Microsoft Access Driver]COUNT field incorrect , SQL state 07001 in SQLExecute in D:\....php on line 30). Here's the code I'm using (Line 30 is odbc_execute): $sql = 'INSERT INTO table ([field0], [field1], [field2], [field3], [field4], [field5]) VALUES (?, ?, ?, ?, ?, ?)'; $stmt = odbc_prepare($conn, $sql); for ($i = 200001; $i < 300001; $i++) { $a = array($i, "Field1 $", "Field2 $i", "Field3 $i", "Field4 $i", $i); odbc_execute($stmt, $a); } So my question is two fold. First, is there any idea on why I'm getting that error (I've checked, and the number in the array matches the field list which matches the number of parameter ? markers)? And second, should I even bother with this or just use the straight INSERT statements? Like I said, time isn't critical, but if it's possible, I'd like to get that time as low as possible (Then again, I may be limited by disk throughput, since 900 operations/sec is high already)... Thanks

    Read the article

  • How to handle product ratings in a database

    - by Mel
    Hello, I would like to know what is the best approach to storing product ratings in a database. I have in mind the following two (simplified, and assuming a MySQL db) scenarios: Scenario 1: Create two columns in the product table to store number of votes and the sum of all votes. Use columns to get an average on the product display page: products(productedID, productName, voteCount, voteSum) Pros: I will only need to access one table, and thus execute one query to display product data and ratings. Cons: Write operations will be executed in a table whose original purpose is only to furnish product data. Scenario 2: Create an additional table to store ratings. products(productID, productName) ratings(productID, voteCount, voteSum) Pros: Isolate ratings into a separate table, leaving the products table to furnish data on available products. Cons: I will have to execute two separate queries on product page requests (one for data and another for ratings). In terms of performance, which of the following two approaches is best: Allow users to execute an occasional write query to a table that will handle hundreds of read requests? Execute two queries at every product page, but isolate the write query into a separate table. I'm a novice to database development, and often find myself struggling with simple questions such as these. Many thanks,

    Read the article

  • The type or namespace name 'WebControls' could not be found (are you missing a using directive or an assembly reference?)

    - by user1467175
    I encountered this error: The type or namespace name 'WebControls' could not be found (are you missing a using directive or an assembly reference?) Source Error: Line 28: Login Login1 = (WebControls.Login)LoginView1.FindControl("Login1"); // here the error code Line 29: TextBox UserName = (TextBox)Login1.FindControl("UserName"); Line 30: TextBox FailureText = (TextBox)Login1.FindControl("FailureText"); I did some research and the solution was to add this into the source code: System.Web.UI.WebControls.Login but I have no idea where this code can be add into. At first I tried putting it as a namespace, but it was wrong. Anyone can tell me where should I place this code at?? EDIT protected void Login1_LoginError(object sender, System.EventArgs e) { //Login Login1 = (WebControls.Login).LoginView1.FindControl("Login1"); Login Login1 = (System.Web.UI.WebControls.Login)LoginView1.FindControl("Login1"); TextBox UserName = (TextBox)Login1.FindControl("UserName"); TextBox FailureText = (TextBox)Login1.FindControl("FailureText"); //There was a problem logging in the user //See if this user exists in the database MembershipUser userInfo = Membership.GetUser(UserName.Text); if (userInfo == null) { //The user entered an invalid username... FailureText.Text = "There is no user in the database with the username " + UserName.Text; } else { //See if the user is locked out or not approved if (!userInfo.IsApproved) { FailureText.Text = "When you created your account you were sent an email with steps to verify your account. You must follow these steps before you can log into the site."; } else if (userInfo.IsLockedOut) { FailureText.Text = "Your account has been locked out because of a maximum number of incorrect login attempts. You will NOT be able to login until you contact a site administrator and have your account unlocked."; } else { //The password was incorrect (don't show anything, the Login control already describes the problem) FailureText.Text = string.Empty; } } }

    Read the article

  • Detect if Download is Complete

    - by user604138
    I have a very simple and standard PHP force download script. How do I check if/when the download has completed in order to notify the user on the clientside? I don't even need to show the progress in real time, I am only interested in the very specific event: "when the download completes". Based on my research, it seems like it would have to be determined from the serverside as there is noondownloadready event and I don't think it is possible to intercept browser events. So it seems that my best bet would be to compare bytes sent to total bytes with some sort of clientside/severside interaction. How would I go about checking the bytes sent from the server for a PHP forced download? is there some sort of global PHP variable that store these data that I can ping with AJAX? <?php header("Content-Type: video/x-msvideo"); header("Content-Disposition: attachment; filename=\"".basename($realpath)."\";"); ... $chunksize = 1 * (1024 * 1024); // how many bytes per chunk if ($size > $chunksize) { $handle = fopen($realpath, 'rb'); $buffer = ''; while (!feof($handle)) { $buffer = fread($handle, $chunksize); echo $buffer; ob_flush(); flush(); } fclose($handle); } else { readfile($realpath); } exit(); ?> The reason I need this: For the project I am working on, it is required that after the download starts, the page redirects to (or displays) a "please wait while the download completes" page. Then, once it is complete, it should redirect to (or display) a "Your download is complete, thank you" page. I am open to other ideas that would achieve the same result.

    Read the article

  • Using enum values to represent binary operators (or functions)

    - by Bears will eat you
    I'm looking for an elegant way to use values in a Java enum to represent operations or functions. My guess is, since this is Java, there just isn't going to be a nice way to do it, but here goes anyway. My enum looks something like this: public enum Operator { LT, LTEQ, EQEQ, GT, GTEQ, NEQ; ... } where LT means < (less than), LTEQ means <= (less than or equal to), etc - you get the idea. Now I want to actually use these enum values to apply an operator. I know I could do this just using a whole bunch of if-statements, but that's the ugly, OO way, e.g.: int a = ..., b = ...; Operator foo = ...; // one of the enum values if (foo == Operator.LT) { return a < b; } else if (foo == Operator.LTEQ) { return a <= b; } else if ... // etc What I'd like to be able to do is cut out this structure and use some sort of first-class function or even polymorphism, but I'm not really sure how. Something like: int a = ..., b = ...; Operator foo = ...; return foo.apply(a, b); or even int a = ..., b = ...; Operator foo = ...; return a foo.convertToOperator() b; But as far as I've seen, I don't think it's possible to return an operator or function (at least, not without using some 3rd-party library). Any suggestions?

    Read the article

  • A good way to write unit tests

    - by bobobobo
    So, I previously wasn't really in the practice of writing unit tests - now I kind of am and I need to check if I'm on the right track. Say you have a class that deals with math computations. class Vector3 { public: // Yes, public. float x,y,z ; // ... ctors ... } ; Vector3 operator+( const Vector3& a, const Vector3 &b ) { return Vector3( a.x + b.y /* oops!! hence the need for unit testing.. */, a.y + b.y, a.z + b.z ) ; } There are 2 ways I can really think of to do a unit test on a Vector class: 1) Hand-solve some problems, then hard code the numbers into the unit test and pass only if equal to your hand and hard-coded result bool UnitTest_ClassVector3_operatorPlus() { Vector3 a( 2, 3, 4 ) ; Vector3 b( 5, 6, 7 ) ; Vector3 result = a + b ; // "expected" is computed outside of computer, and // hard coded here. For more complicated operations like // arbitrary axis rotation this takes a bit of paperwork, // but only the final result will ever be entered here. Vector3 expected( 7, 9, 11 ) ; if( result.isNear( expected ) ) return PASS ; else return FAIL ; } 2) Rewrite the computation code very carefully inside the unit test. bool UnitTest_ClassVector3_operatorPlus() { Vector3 a( 2, 3, 4 ) ; Vector3 b( 5, 6, 7 ) ; Vector3 result = a + b ; // "expected" is computed HERE. This // means all you've done is coded the // same thing twice, hopefully not having // repeated the same mistake again Vector3 expected( 2 + 5, 6 + 3, 4 + 7 ) ; if( result.isNear( expected ) ) return PASS ; else return FAIL ; } Or is there another way to do something like this?

    Read the article

  • Implementing comparision operators via 'tuple' and 'tie', a good idea?

    - by Xeo
    (Note: tuple and tie can be taken from Boost or C++11.) When writing small structs with only two elements, I sometimes tend to choose a std::pair, as all important stuff is already done for that datatype, like operator< for strict-weak-ordering. The downsides though are the pretty much useless variable names. Even if I myself created that typedef, I won't remember 2 days later what first and what second exactly was, especially if they are both of the same type. This gets even worse for more than two members, as nesting pairs pretty much sucks. The other option for that is a tuple, either from Boost or C++11, but that doesn't really look any nicer and clearer. So I go back to writing the structs myself, including any needed comparision operators. Since especially the operator< can be quite cumbersome, I thought of circumventing this whole mess by just relying on the operations defined for tuple: Example of operator<, e.g. for strict-weak-ordering: bool operator<(MyStruct const& lhs, MyStruct const& rhs){ return std::tie(lhs.one_member, lhs.another, lhs.yet_more) < std::tie(rhs.one_member, rhs.another, rhs.yet_more); } (tie makes a tuple of T& references from the passed arguments.) Edit: The suggestion from @DeadMG to privately inherit from tuple isn't a bad one, but it got quite some drawbacks: If the operators are free-standing (possibly friends), I need to inherit publicly With casting, my functions / operators (operator= specifically) can be easily bypassed With the tie solution, I can leave out certain members if they don't matter for the ordering Are there any drawbacks in this implementation that I need to consider?

    Read the article

< Previous Page | 245 246 247 248 249 250 251 252 253 254 255 256  | Next Page >