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• How to efficiently convert String, integer, double, datetime to binary and vica versa?

  - by Ben

  Hi, I'm quite new to C# (I'm using .NET 4.0) so please bear with me. I need to save some object properties (their properties are int, double, String, boolean, datetime) to a file. But I want to encrypt the files using my own encryption, so I can't use FileStream to convert to binary. Also I don't want to use object serialization, because of performance issues. The idea is simple, first I need to somehow convert objects (their properties) to binary (array), then encrypt (some sort of xor) the array and append it to the end of the file. When reading first decrypt the array and then somehow convert the binary array back to object properties (from which I'll generate objects). I know (roughly =) ) how to convert these things by hand and I could code it, but it would be useless (too slow). I think the best way would be just to get properties' representation in memory and save that. But I don't know how to do it using C# (maybe using pointers?). Also I though about using MemoryStream but again I think it would be inefficient. I am thinking about class Converter, but it does not support toByte(datetime) (documentation says it always throws exception). For converting back I think the only options is class Converter. Note: I know the structure of objects and they will not change, also the maximum String length is also known. Thank you for all your ideas and time. EDIT: I will be storing only parts of objects, in some cases also parts of different objects (a couple of properties from one object type and a couple from another), thus I think that serialization is not an option for me.

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• How do I cast a void pointer to a struct in C?

  - by Rowhawn

  In a project I'm writing code for, I have a void pointer, "implementation", which is a member of a "Hash_map" struct, and points to an "Array_hash_map" struct. The concepts behind this project are not very realistic, but bear with me. The specifications of the project ask that I cast the void pointer "implementation" to an "Array_hash_map" before I can use it in any functions. My question, specifically is, what do I do in the functions to cast the void pointers to the desired struct? Is there one statement at the top of each function that casts them or do I make the cast every time I use "implementation"? Here are the typedefs the structs of a Hash_map and Array_hash_map as well as a couple functions making use of them. typedef struct { Key_compare_fn key_compare_fn; Key_delete_fn key_delete_fn; Data_compare_fn data_compare_fn; Data_delete_fn data_delete_fn; void *implementation; } Hash_map; typedef struct Array_hash_map{ struct Unit *array; int size; int capacity; } Array_hash_map; typedef struct Unit{ Key key; Data data; } Unit; functions: /* Sets the value parameter to the value associated with the key parameter in the Hash_map. */ int get(Hash_map *map, Key key, Data *value){ int i; if (map == NULL || value == NULL) return 0; for (i = 0; i < map->implementation->size; i++){ if (map->key_compare_fn(map->implementation->array[i].key, key) == 0){ *value = map->implementation->array[i].data; return 1; } } return 0; } /* Returns the number of values that can be stored in the Hash_map, since it is represented by an array. */ int current_capacity(Hash_map map){ return map.implementation->capacity; }

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• Accessing bitmap array in another class? C#

  - by Marius Mathisen

  I have this array : Bitmap[] bildeListe = new Bitmap[21]; bildeListe[0] = Properties.Resources.ål; bildeListe[1] = Properties.Resources.ant; bildeListe[2] = Properties.Resources.bird; bildeListe[3] = Properties.Resources.bear; bildeListe[4] = Properties.Resources.butterfly; bildeListe[5] = Properties.Resources.cat; bildeListe[6] = Properties.Resources.chicken; bildeListe[7] = Properties.Resources.dog; bildeListe[8] = Properties.Resources.elephant; bildeListe[9] = Properties.Resources.fish; bildeListe[10] = Properties.Resources.goat; bildeListe[11] = Properties.Resources.horse; bildeListe[12] = Properties.Resources.ladybug; bildeListe[13] = Properties.Resources.lion; bildeListe[14] = Properties.Resources.moose; bildeListe[15] = Properties.Resources.polarbear; bildeListe[16] = Properties.Resources.reke; bildeListe[17] = Properties.Resources.sheep; bildeListe[18] = Properties.Resources.snake; bildeListe[19] = Properties.Resources.spider; bildeListe[20] = Properties.Resources.turtle; I want that array and it´s content in a diffenrent class, and access it from my main form. I don´t know if should use method, function or what to use with arrays. Are there some good way for me to access for instanse bildeListe[0] in my new class?

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• BlackBerry Deployment Strategies

  - by cagreen

  I'm new to large scale BB app deployment and I'm looking for some clarification on the various methods of deployment. Please bear with me as I'm sure there is more to it than my naive view would lead me to believe. My app is very targeted to corporate users and requires a subscription to some additional services before it can be used. In other words, it's not targeted towards the consumer market, so I'm not worried about people not being able to easily find it online. What do I need to be aware of when looking at deployment strategies? Any gotchas? From my understanding my choices are: - App World small upfront vendor fee users can easily search for and find my app billing handled by RIM 4 licensing models (static, single, pool, dynamic). Though I'm not sure I've seen enough info on the pool and dynamic to fully appreciate how it might help me. - Download from my website billing is handled by me can I enforce the number of licenses that are in use within an organization? is this easier/harder for a user? - What else am I missing?

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• C++ data member initializer is not allowed

  - by user1435915

  I totally new to C++ so bear with me. I want to make a class with a static array, and access to this array from the main. Here is what i want to do in C#. namespace ConsoleApplication1 { class Program { static void Main(string[] args) { Class a = new Class(); Console.WriteLine(a.arr[1]); } } } ===================== namespace ConsoleApplication1 { class Class { public static string[] s_strHands = new string[]{"one","two","three"}; } } Here is what i have tried: // justfoolin.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include <string> #include <iostream> using namespace std; class Class { public: static string arr[3] = {"one", "two", "three"}; }; int _tmain(int argc, _TCHAR* argv[]) { Class x; cout << x.arr[2] << endl; return 0; } But i got: IntelliSense: data member initializer is not allowed

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• Filp route value in asp.net mvc routes

  - by Herman

  Hi all, I am new to asp.net mvc, so please bear with me. We have the following route dictionary setup. routes.MapRoute( "Default", // Route name "{language}/{controller}/{action}/{id}", // URL with parameters new { language = "en", controller = "Home", action = "Index", id = "" } // Parameter defaults ); for any given page in our app, we to render a link to the a french version of the same page. For example, the page: http://www.example.com/en/home should have link on that page that points to http://www.example.com/fr/home Now I have the following UrlHelper extension method public static string FilpLanguage(this UrlHelper urlHelper) { var data = urlHelper.RequestContext.RouteData; if (System.Threading.Thread.CurrentThread.CurrentCulture == CultureInfo.GetCultureInfoByIetfLanguageTag("en-CA")) data.Values["language"] = "fr"; else data.Values["language"] = "en"; return urlHelper.RouteUrl(data.Values.Where(item => item.Value != null)); } However, calling FilpLanguage on www.example.com/en/home will return the following URL: www.example.com/en/home?current=[,] Am I missing something here? where did the current parameter come from? Thanks in advance.

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• How can I use SQL to select duplicate records, along with counts of related items?

  - by mipadi

  I know the title of this question is a bit confusing, so bear with me. :) I have a (MySQL) database with a Person record. A Person also has a slug field. Unfortunately, slug fields are not unique. There are a number of duplicate records, i.e., the records have different IDs but the same first name, last name, and slug. A Person may also have 0 or more associated articles, blog entries, and podcast episodes. If that's confusing, here's a diagram of the structure: I would like to produce a list of records that match this criteria: duplicate records (i.e., same slug field) for people who also have at least 1 article, blog entry, or podcast episode. I have a SQL query that will list all records with the same slug fields: SELECT id, first_name, last_name, slug, COUNT(slug) AS person_records FROM people_person GROUP BY slug HAVING (COUNT(slug) > 1) ORDER BY last_name, first_name, id; But this includes records for people that may not have at least 1 article, blog entry, or podcast. Can I tweak this to fit the second criteria?

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• A question about entities, roles and interfaces in Entity Framework 4.

  - by mvole

  Hi, I am an experienced .NET developer but new to EF - so please bear with me. I will use an example of a college application to illustrate my problem. I have these user roles: Lecturer, Student, Administrator. In my code I envisage working with these entities as distinct classes so e.g. a Lecturer teaches a collection of Students. And work with 'is Student' 'TypeOf' etc. Each of these entities share lots of common properties/methods e.g. they can all log onto the system and do stuff related to their role. In EF designer I can create a base entity Person (or User...) and have Lecturer, Student and Administrator all inherit from that. The difficulty I have is that a Lecturer can be an Administrator - and in fact on occasion a Student can be a Lecturer. If I were to add other entities such as Employee and Warden then this gets even more of an issue. I could presumably work with Interfaces so a person could implement ILecturer and IStudent, however I do not see how this fits within EF. I would like to work within the EF designer if possible and I'm working model-first (coding in C#). So any help and advice/samples would be very welcome and much appreciated. Thanks

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• open current page in new window including query string

  - by Hatch

  First of all, I am a total dud at all things related to web developement, so please bear with me here. I suspect this question is laughable for the web guys, but unfortunately I can't figure this out. Here goes: I have an application, that does some processing, writes some result files and then displays the results in an embedded IE browser control. This is done by navigating the browser control to a local html file together with a query string containing the generated result files to display it all. The link target would look something like: c:\SomeFolder\results.htm?results=file%201.xml;file%202.xml;file%203.xml So far, everything's fine. However, in the html page is a href that is suppossed to open up the exact same just in a normal browser window. What I thought would work is: <a href="#" target="_blank">Show in browser</a> Since it is a link in an html page displayed in an IE control, the link will open up in IE no matter what the default browser might be. This works for IE7 and 8, but not for IE6. With IE6 the query string gets cut off and the browser opens file://c:/results/results.htm# without the query string. I am sure there must be a much better way to do this without the # and which would work in all IEs. How would the pros solve this?

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• SQL Server 2008 R2

  - by kevchadders

  Hi all, I heard on the grapevine that Microsoft will be releasing SQL Server 2008 R2 within a year. Though I initially thought this was a patch for the just released 2008 version, I realised that it’s actually a completely different version that you would have to pay for. (Am I correct, if you had SQL Server 2008, would you have to pay again if you wanted to upgrade to 2008 R2?) If you’re already running SQL Server 2008, would you say it’s still worth the upgrade? Or does it depend on the size of your company and current setup. For what I’ve initially read, I do get the impression that this version would be more useful for the very high end hardware setup where you want to have very good scalability. With regard to programming, is there any extra enhancements/support in there which you’re aware of that will significantly help .NET Products/Web Development? Initially found a couple of links on it, but I was wondering if anyone had anymore info to share on subject as I couldn’t find nothing on SO about it? Thanks. New SQL Server R2 Microsoft Link on it. Microsoft SQL 2008 R2 EDIT: More information based on the Express Edition One very interesting thing about SQL Server 2008 R2 concerns the Express edition. Previous express versions of SQL Server Express had a database size limit of 4GB. With SQL Server Express 2008 R2, this has now been increased to 10GB !! This now makes the FREE express edition a much more viable option for small & medium sized applications that are relatively light on database requirements. Bear in mind, that this limit is per database, so if you coded your application cleverly enough to use a separate database for historical/archived data, you could squeeze even more out of it! For more information, see here: http://blogs.msdn.com/sqlexpress/archive/2010/04/21/database-size-limit-increased-to-10gb-in-sql-server-2008-r2-express.aspx

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• C++ polymorphism, function calls

  - by moai

  Okay, I'm pretty inexperienced as a programmer, let alone in C++, so bear with me here. What I wanted to do was to have a container class hold a parent class pointer and then use polymorphism to store a child class object. The thing is that I want to call one of the child class's functions through the parent class pointer. Here's a sort of example of what I mean in code: class SuperClass { public: int x; } class SubClass : public SuperClass { public: void function1() { x += 1; } } class Container { public: SuperClass * alpha; Container(SuperClass& beta) { alpha = beta; } } int main() { Container cont = new Container(new SubClass); } (I'm not sure that's right, I'm still really shaky on pointers. I hope it gets the point across, at least.) So, I'm not entirely sure whether I can do this or not. I have a sneaking suspicion the answer is no, but I want to be sure. If someone has another way to accomplish this sort of thing, I'd be glad to hear it.

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• sql server mdf file database attachment

  - by jnsohnumr

  hello all i'm having a bear of a time getting visual studio 2010 (ultimate i think) to properly attach to my database. it was moved from original spot to #MYAPP#/#MYAPP#.Web/App_Data/#MDF_FILE#.mdf. I have three instances of sql server running on this machine. i have tried to replace the old mdf file with my new one and cannot get the connectionstring right for it. what i'm really wanting to do is to just open some DB instance, run a DB create script. Then I can have a DB that was generated via my edmx (generate database from model) in silverlight business application (c#) right now, when i go to server explorer in VS, choose add new connection, choose MS SQL Server Database FIle (SqlClient), choose my file location (app_data directory), use windows authentication, and hit the Test Connection button I get the following error: Unable to open the physical file "". Operating system error 5: "5(Access Denied.)". An attempt to attach to an auto-named database for file"" failed. A database with the same name exists, or specified file cannot be opened, or it is located on UNC share. The mdf file was created on the same machine by connecting to (local) on the sql server management studio, getting a new query, pasting in the SQL from the generated ddl file, adding a CREATE DATABASE [NcrCarDatabase]; GO before the pasted SQL, and executing the query. I then disconnected from the DB in management studio, closed management studio, navigated to the DATA directory for that instance, and copying the mdf and ldf files to my application's app_data folder. I am then trying to connect to the same file inside visual studio. I hope that gives more clarity to my problems :). Connection string is: Data Source=.\SQLEXPRESS;AttachDbFilename=C:\SourceCode\NcrCarDatabase\NcrCarDatabase.Web\App_Data\NcrCarDatabase.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True

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• Creating a HTTP handler for IIS that transparently forwards request to different port?

  - by Lasse V. Karlsen

  I have a public web server with the following software installed: IIS7 on port 80 Subversion over apache on port 81 TeamCity over apache on port 82 Unfortunately, both Subversion and TeamCity comes with their own web server installations, and they work flawlessly, so I don't really want to try to move them all to run under IIS, if that is even possible. However, I was looking at IIS and I noticed the HTTP redirect part, and I was wondering... Would it be possible for me to create a HTTP handler, and install it on a sub-domain under IIS7, so that all requests to, say, http://svn.vkarlsen.no/anything/here is passed to my HTTP handler, which then subsequently creates a request to http://localhost:81/anything/here, retrieves the data, and passes it on to the original requestee? In other words, I would like IIS to handle transparent forwards to port 81 and 82, without using the redirection features. For instance, Subversion doesn't like HTTP redirect and just says that the repository has been moved, and I need to relocate my working copy. That's not what I want. If anyone thinks this can be done, does anyone have any links to topics I need to read up on? I think I can manage the actual request parts, even with authentication, but I have no idea how to create a HTTP handler. Also bear in mind that I need to handle sub-paths and documents beneath the top-level domain, so http://svn.vkarlsen.no/whatever/here needs to be handled by a single handler, I cannot create copies of the handler for all sub-directories since paths are created from time to time.

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• Is it "right" to translate error messages?

  - by Iraklis

  This is somehow subjective depending on the target translation language, but bear with me for a sec. I have recently been involved in a translation project. The goal was to translate the strings of an MVC framework to the Greek language. 70% of the language strings of the framework where translated, however 30% where intentionally left out. The decision was that we will not translate error messages aimed towards the developer of the application. The reasoning behind this (in short) was: are aimed towards designers/programmers. Programmers ( and even designers :) ) should have a basic understanding of English, at least enough so they can search on it on Google if they do not know what it means. (racist?) are aimed towards the developer and in a perfect world should not be displayed to the end user of the application as they concern the inner workings of the web application itself. i.e "You must set the database name in your database config file." and perhaps most importantly, they make the life of the developer harder when he tries to get more information/help regarding the error. For example the above error yields 8 results in Google (in quotes), whereas its Greek translation yields exactly 0. I know that this depends on the popularity of the target translation language and the application itself. For example I'm guessing that there are is vast amount of documentation regarding German SAP error messages (i know, i know, SAP IS German, but you get the point), as opposed to Greek Error Messages documentation regarding random application X which has about 500 installations worldwide. So to summarize: When you develop language translation packs for your applications do you translate error messages? Do you only do for predominant languages like English/Spanish/German/French? Or do you live them intact? I'm not looking for the "right" or "correct" answer, I'm looking for a "best-practices" answer, or if this problem is defined in any "official" standard/policy that you have had experience with.

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• Using different numeric variable types

  - by DataPimp

  Im still pretty new so bear with me on this one, my question(s) are not meant to be argumentative or petty but during some reading something struck me as odd. Im under the assumption that when computers were slow and memory was expensive using the correct variable type was much more of a necessity than it is today. Now that memory is a bit easier to come by people seem to have relaxed a bit. For example, you see this sample code everywhere: for (int i = 0; i < length; i++) int? (-2,147,483,648 to 2,147,483,648) for length? Isnt byte (0-255) a better choice? So Im curious of your opinion and what you believe to be best practice, I hate to think this would be used only because the acronym "int" is more intuitive for a beginner...or has memory just become so cheap that we really dont need to concern ourselves with such petty things and therefore we should just use long so we can be sure any other numbers/types(within reason) used can be cast automagically? ...or am Im just being silly by concerning myself with such things?

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• PHP include doesn't work

  - by Chris

  I'm not sure how simple is this to solve, but I assume I'm doing something wrong. I'm new to PHP, so bear with me, please. When I started learning PHP, I always placed all my project files into the same folder along with index.php and thus included everything like this: <?php include('./translation.php'); ?> Later on in the process of learning as I gained experience and my skill increased, I had to start using folders and place my files into sub folders. I ended up successfully including my files with the following: <?php include('../translation.php'); ?> My trouble-free coding took an unexpected turn when I decided to start using sub-sub folders. After placing all the files even deeper into the file structure I was shocked to find out that I cannot include them anymore, using: <?php include('.../translation.php'); ?> Now I'm lost. What did I do wrong? Am I to understand that I cannot include files deeper than 2 directories in the project? Should I start using a different file system?

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• If attacker has original data, and encrypted data, can they determine the passphrase?

  - by Brad Cupit

  If an attacker has several distinct items (for example: e-mail addresses) and knows the encrypted value of each item, can the attacker more easily determine the secret passphrase used to encrypt those items? Meaning, can they determine the passphrase without resorting to brute force? This question may sound strange, so let me provide a use-case: User signs up to a site with their e-mail address Server sends that e-mail address a confirmation URL (for example: https://my.app.com/confirmEmailAddress/bill%40yahoo.com) Attacker can guess the confirmation URL and therefore can sign up with someone else's e-mail address, and 'confirm' it without ever having to sign in to that person's e-mail account and see the confirmation URL. This is a problem. Instead of sending the e-mail address plain text in the URL, we'll send it encrypted by a secret passphrase. (I know the attacker could still intercept the e-mail sent by the server, since e-mail are plain text, but bear with me here.) If an attacker then signs up with multiple free e-mail accounts and sees multiple URLs, each with the corresponding encrypted e-mail address, could the attacker more easily determine the passphrase used for encryption? Alternative Solution I could instead send a random number or one-way hash of their e-mail address (plus random salt). This eliminates storing the secret passphrase, but it means I need to store that random number/hash in the database. The original approach above does not require this extra table. I'm leaning towards the the one-way hash + extra table solution, but I still would like to know the answer: does having multiple unencrypted e-mail addresses and their encrypted counterparts make it easier to determine the passphrase used?

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• django test client trouble

  - by Anton Koval'

  I've got a problem... we're writing project using django, and i'm trying to use django.test.client with nose test-framework for tests. Our code is like this: from simplejson import loads from urlparse import urljoin from django.test.client import Client TEST_URL = "http://smakly.localhost:9090/" def test_register(): cln = Client() ref_data = {"email": "[email protected]", "name": "???????", "website": "http://hot.bear.com", "xhr": "true"} print urljoin(TEST_URL, "/accounts/register/") response = loads(cln.post(urljoin(TEST_URL, "/accounts/register/"), ref_data)) print response["message"] and in nose output I catch: Traceback (most recent call last): File "/home/psih/work/svn/smakly/eggs/nose-0.11.1-py2.6.egg/nose/case.py", line 183, in runTest self.test(*self.arg) File "/home/psih/work/svn/smakly/src/smakly.tests/smakly/tests/frontend/test_profile.py", line 25, in test_register response = loads(cln.post(urljoin(TEST_URL, "/accounts/register/"), ref_data)) File "/home/psih/work/svn/smakly/parts/django/django/test/client.py", line 313, in post response = self.request(**r) File "/home/psih/work/svn/smakly/parts/django/django/test/client.py", line 225, in request response = self.handler(environ) File "/home/psih/work/svn/smakly/parts/django/django/test/client.py", line 69, in __call__ response = self.get_response(request) File "/home/psih/work/svn/smakly/parts/django/django/core/handlers/base.py", line 78, in get_response urlconf = getattr(request, "urlconf", settings.ROOT_URLCONF) File "/home/psih/work/svn/smakly/parts/django/django/utils/functional.py", line 273, in __getattr__ return getattr(self._wrapped, name) AttributeError: 'Settings' object has no attribute 'ROOT_URLCONF' My settings.py file does have this attribute. If I get the data from the server with standard urllib2.urllopen().read() it works in the proper way. Any ideas how I can solve this case?

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• Jquery find first visible element after horizontal scroll

  - by lolo flores

  I’m new (only two weeks old) in Jquery, so please bear with me. I know that a very similar question was asked some time ago but I do not know how to adapt the answer to my problem. I have a very wide multicolumn layout something like this: | aaaa | bbbb | cccc | … | | aaaa | b | cc | … | | aaa | cccc | ddd | … | The code looks like: <div id="container"> <p>aaaaaaaaaaa</p> <p>bbbbb</p> <p>ccccccccccc</p> <p>dddddddddd</p> ... <p>xxxxxx</p> </div> There is no vertical scrolling and the container width is set in such a way that only two columns are shown. The user scrolls left or right to see the relevant text. What I want is to get the position currently on display, store it (maybe in a cookie) and retrieve it the next time the user opens the page. I think that I need a way of finding out what paragraph is currently the left-top most, but other suggestions are very welcome. Any ideas? btw: this is an internal project, so Mozilla only :-) Thanks Lolo

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• C# "Rename" Property in Derived Class

  - by Eric

  When you read this you'll be awfully tempted to give advice like "this is a bad idea for the following reason..." Bear with me. I know there are other ways to approach this. This question should be considered trivia. Lets say you have a class "Transaction" that has properties common to all transactions such as Invoice, Purchase Order, and Sales Receipt. Let's take the simple example of Transaction "Amount", which is the most important monetary amount for a given transaction. public class Transaction { public double Amount { get; set; } public TxnTypeEnum TransactionType { get; set; } } This Amount may have a more specific name in a derived type... at least in the real world. For example, the following values are all actually the same thing: Transaction - Amount Invoice - Subtotal PurchaseOrder - Total Sales Receipt - Amount So now I want a derived class "Invoice" that has a Subtotal rather than the generically-named Amount. Ideally both of the following would be true: In an instance of Transaction, the Amount property would be visible. In an instance of Invoice, the Amount property would be hidden, but the Subtotal property would refer to it internally. Invoice looks like this: public class Invoice : Transaction { new private double? Amount { get { return base.Amount; } set { base.Amount = value; } } // This property should hide the generic property "Amount" on Transaction public double? SubTotal { get { return Amount; } set { Amount = value; } } public double RemainingBalance { get; set; } } But of course Transaction.Amount is still visible on any instance of Invoice. Thanks for taking a look!

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• Is it possible to customize @synthesized properties?

  - by Dan K.

  I'm probably just being a bit lazy here, but bear with me. Here's my situation. I have a class with two nonatomic, retained properties. Let's say: @property (nonatomic, retain) UITextField *dateField; @property (nonatomic, retain) NSDate *date; I synthesize them as expected in the implementation. What I want to happen is that whenever the setter on date is invoked, it also does something to the dateField (i.e. it sets the text property on the dateField to be a nicely formatted version of the date). I realize I can just manually override the setter for date in my implementation by doing the following: - (void) setDate:(NSDate *)newDate { if (date != newDate) { [date release]; date = [newDate retain]; // my code to touch the dateField goes here } } What would be awesome is if I could let Objective C handle the retain/release cycle, but still be able to "register" (for lack of a better term) a custom handler that would be invoked after the retain/release/set happens. My guess is that isn't possible. My google-fu didn't come up with any answer to this, though, so I thought I'd ask.

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• Help! I'm a Haskell Newbie

  - by Darknight

  I've only just dipped my toe in the world of Haskell as part of my journey of programming enlightenment (moving on from, procedural to OOP to concurrent to now functional). I've been trying an online Haskell Evaluator. However I'm now stuck on a problem: Create a simple function that gives the total sum of an array of numbers. In a procedural language this for me is easy enough (using recursion) (c#) : private int sum(ArrayList x, int i) { if (!(x.Count < i + 1)) { int t = 0; t = x.Item(i); t = sum(x, i + 1) + t; return t; } } All very fine however my failed attempt at Haskell was thus: let sum x = x+sum in map sum [1..10] this resulted in the following error (from that above mentioned website): Occurs check: cannot construct the infinite type: a = a -> t Please bear in mind I've only used Haskell for the last 30 minutes! I'm not looking simply for an answer but a more explanation of it. Thanks in advanced.

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• Complicated .NET factory design

  - by Tom W

  Hello SO; I'm planning to ask a fairly elaborate question that is also something of a musing here, so bear with me... I'm trying to design a factory implementation for a simulation application. The simulation will consist of different sorts of entities i.e. it is not a homogenous simulation in any respect. As a result, there will be numerous very different concrete implementations and only the very general properties will be abstracted at the top level. What I'd like to be able to do is create new simulation entities by calling a method on the model with a series of named arguments representing the parameters of the entity, and have the model infer what type of object is being described by the inbound parameters (from the names of the parameters and potentially the sequence they occur in) and call a factory method on the appropriate derived class. For example, if I pass the model a pair of parameters (Param1=5000, Param2="Bacon") I would like it to infer that the names Param1 and Param2 'belong' to the class "Blob1" and call a shared function "getBlob1" with named parameters Param1:=5000, Param2:="Bacon" whereas if I pass the model (Param1=5000, Param3=50) it would call a similar factory method for Blob2; because Param1 and Param3 in that order 'belong' to Blob2. I foresee several issues to resolve: Whether or not I can reflect on the available types with string parameter names and how to do this if it's possible Whether or not there's a neat way of doing the appropriate constructor inference from the combinatoric properties of the argument list or whether I'm going to have to bodge something to do it 'by hand'. If possible I'd like the model class to be able to accept parameters as parameters rather than as some collection of keys and values, which would require the model to expose a large number of parametrised methods at runtime without me having to code them explicitly - presumably one for every factory method available in the relevant namespace. What I'm really asking is how you'd go about implementing such a system, rather than whether or not it's fundamentally possible. I don't have the foresight or experience with .NET reflection to be able to figure out a way by myself. Hopefully this will prove an informative discussion.

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• Extended slice that goes to beginning of sequence with negative stride

  - by recursive

  Bear with me while I explain my question. Skip down to the bold heading if you already understand extended slice list indexing. In python, you can index lists using slice notation. Here's an example: >>> A = list(range(10)) >>> A[0:5] [0, 1, 2, 3, 4] You can also include a stride, which acts like a "step": >>> A[0:5:2] [0, 2, 4] The stride is also allowed to be negative, meaning the elements are retrieved in reverse order: >>> A[5:0:-1] [5, 4, 3, 2, 1] But wait! I wanted to see [4, 3, 2, 1, 0]. Oh, I see, I need to decrement the start and end indices: >>> A[4:-1:-1] [] What happened? It's interpreting -1 as being at the end of the array, not the beginning. I know you can achieve this as follows: >>> A[4::-1] [4, 3, 2, 1, 0] But you can't use this in all cases. For example, in a method that's been passed indices. My question is: Is there any good pythonic way of using extended slices with negative strides and explicit start and end indices that include the first element of a sequence? This is what I've come up with so far, but it seems unsatisfying. >>> A[0:5][::-1] [4, 3, 2, 1, 0]

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• My Rails session is getting reset when I have concurrent requests

  - by alex_c

  I think I might be misunderstanding something about Rails sessions, so please bear with me, I might not be phrasing my question the best way. I'm working on an iPhone app with a Ruby on Rails backend. I have a web view which by default goes to the index action of one controller (and uses sessions), and in the background a bunch of API calls going to a different controller (and which don't need to use sessions). The problem is, the sessions set by my web view seem to be overwitten by the API calls. My staging server is pretty slow, so there's lots of time for the requests to overlap each other - what I see in the logs is basically this: Request A (first controller) starts. Session is empty. Request B (second controller) starts. Session is empty. Request A finishes. Request A has done authentication, and stored the user ID in the session. Session contains user ID. Request B finishes. Session is empty. Request C starts. Session is empty - not what I want. Now, the strange thing is that request B should NOT be writing anything to the session. I do have before and after filters which READ from the session - things like: user = User.find_by_id(session[:id]) or logger.debug session.inspect and if I remove all of those, then everything works as expected - session contents get set by request A, and they're still there when request C starts. So. I think I'm missing something about how sessions work. Why would reading from the session overwrite it? Should I be accessing it some other way? Am I completely on the wrong track and the problem is elsewhere? Thank you for any insights!

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