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  • Linq DateTime expressions wont compare if only one is nullable

    - by tigermain
    I have been getting the following exception: The binary operator GreaterThanOrEqual is not defined for the types 'System.Nullable`1[System.DateTime]' and 'System.DateTime'. I am getting the left hand expression from a class property which is a nullable datetime variable and my right hand side is using Expression.Constant(new Nullable<DateTime>(DateTime.Now)) However I still get the above exception despite explicitly setting the right hand expression to a nullable type

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  • Is there any reason for an object pool to not be treated as a singleton?

    - by Chris Charabaruk
    I don't necessarily mean implemented using the singleton pattern, but rather, only having and using one instance of a pool. I don't like the idea of having just one pool (or one per pooled type). However, I can't really come up with any concrete situations where there's an advantage to multiple pools for mutable types, at least not any where a single pool can function just as well. What advantages are there to having multiple pools over a singleton pool?

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  • How do I avoid web method parameters using proxy classes?

    - by Alex Angas
    I have a serializable POCO called DataUnification.ClientData.ClientInfo in a .NET class library project A. It's used in a parameter for a web service defined in project B: public XmlDocument CreateNewClient(ClientInfo ci, string system) I now wish to call this web method from project C and use the original DataUnification.ClientData.ClientInfo type in the parameter. However due to the generated proxy class it has now become a different type: WebServices.ClientDataUnification.DataUnificationWebService.ClientInfo. As far as .NET is concerned these are not the same types. How can I get around this?

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  • Where can one find free software icons / images?

    - by mmattax
    This may not be directly related to programming, but I always find it hard to get quality icons that can be used for software. I currently have the need for some type of "green checkmark image", and I always seem to be looking for print, save, delete types of icons... Anybody have good resources? Note: I rather not be stealing someone's intellectual property.

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  • Const unsigned char* to char8

    - by BSchlinker
    So, I have two types at the moment: const unsigned char* unencrypted_data_char; string unencrypted_data; I'm attempting to perform a simple conversion of data from one to the other (string - const unsigned char*) As a result, I have the following: strcpy((unencrypted_data_char),(unencrypted_data.c_str())); However, I'm receiving the error: error C2664: 'strcpy' : cannot convert parameter 1 from 'const unsigned char *' to 'char *' Any advise? I thought using reinterpret_cast would help, but it doesn't seem to make a difference.

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  • Should the PHP community start using more discriptive Exceptions?

    - by fireeyedboy
    I work with Zend Framework a lot and I just took a peek at Kohana, and it strikes me as odd that this is a typical scenario in these frameworks: throw Some_Componenents_Exception( 'invalid argument' ); Where I believe this wouldn't be mouch more useful: throw Some_Components_InvalidArgumentException( 'whatever discription' ); Because it is easier to catch. I suspect, but immediately admit it's prejudiced, that the former practice is common in the PHP community. Should we, the PHP community, start using these descriptive types of expections more?

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  • Tomcat v7.0 failed to start on Eclipse

    - by Questions
    Whenever I am running a program on Eclipse, my tomcat is failing to start. I get a dialog box stating this message Server Tomcat v7.0 Server at localhost failed to start. In the console, I am getting this messages Nov 17, 2011 11:56:04 AM org.apache.catalina.core.AprLifecycleListener init INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Program Files\Java\jre6\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:/Program Files/Java/jre6/bin/client;C:/Program Files/Java/jre6/bin;C:/Program Files/Java/jre6/lib/i386;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\Program Files\Intel\WiFi\bin\;C:\Program Files\Java\jdk1.6.0_01\bin;C:\Program Files\Java\jre1.6.0_01\bin;C:\ILOG\CPLEX_Studio_Preview122\opl\bin\x86_win32;C:\ILOG\CPLEX_Studio_Preview122\opl\oplide\;C:\ILOG\CPLEX_Studio_Preview122\cplex\bin\x86_win32;C:\ILOG\CPLEX_Studio_Preview122\cpoptimizer\bin\x86_win32;;D:\JSP_Setup\eclipse-jee-helios-SR2-win32\eclipse;;. Nov 17, 2011 11:56:04 AM org.apache.tomcat.util.digester.SetPropertiesRule begin WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:servletConfigTest' did not find a matching property. Nov 17, 2011 11:56:04 AM org.apache.tomcat.util.digester.SetPropertiesRule begin WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:BeerAdvice3' did not find a matching property. Nov 17, 2011 11:56:04 AM org.apache.tomcat.util.digester.SetPropertiesRule begin WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.jee.server:BeerAdvice1' did not find a matching property. Nov 17, 2011 11:56:05 AM org.apache.coyote.http11.Http11Protocol init INFO: Initializing Coyote HTTP/1.1 on http-8080 Nov 17, 2011 11:56:05 AM org.apache.coyote.ajp.AjpProtocol init INFO: Initializing Coyote AJP/1.3 on ajp-8009 Nov 17, 2011 11:56:05 AM org.apache.catalina.startup.Catalina load INFO: Initialization processed in 682 ms Nov 17, 2011 11:56:05 AM org.apache.catalina.core.StandardService startInternal INFO: Starting service Catalina Nov 17, 2011 11:56:05 AM org.apache.catalina.core.StandardEngine startInternal INFO: Starting Servlet Engine: Apache Tomcat/7.0.2 java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288) at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:415) Caused by: java.lang.IllegalArgumentException: Invalid <url-pattern> entry_checking in servlet mapping at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:2823) at org.apache.catalina.core.StandardContext.addServletMapping(StandardContext.java:2799) at org.apache.catalina.deploy.WebXml.configureContext(WebXml.java:1278) at org.apache.catalina.startup.ContextConfig.webConfig(ContextConfig.java:1255) at org.apache.catalina.startup.ContextConfig.configureStart(ContextConfig.java:878) at org.apache.catalina.startup.ContextConfig.lifecycleEvent(ContextConfig.java:313) at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119) at org.apache.catalina.util.LifecycleBase.fireLifecycleEvent(LifecycleBase.java:89) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:4667) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:988) at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:771) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139) at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:988) at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:275) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139) at org.apache.catalina.core.StandardService.startInternal(StandardService.java:427) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139) at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:649) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:139) at org.apache.catalina.startup.Catalina.start(Catalina.java:585) ... 6 more I had run the code previously, but now it is giving this problems. Also, I went through this post http://forums.opensuse.org/applications/391114-tomcat6-eclipse-not-working.html But is not helping me. Please help at the earliest.

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  • Trouble passing a template function as an argument to another function in C++

    - by Darel
    Source of the problem -Accelerated C++, problem 8-5 I've written a small program that examines lines of string input, and tallies the number of times a word appears on a given line. The following code accomplishes this: #include <map> #include <iostream> #include <string> #include <vector> #include <list> #include <cctype> #include <iterator> using std::vector; using std::string; using std::cin; using std::cout; using std::endl; using std::getline; using std::istream; using std::string; using std::list; using std::map; using std::isspace; using std::ostream_iterator; using std::allocator; inline void keep_window_open() { cin.clear(); cout << "Please enter EOF to exit\n"; char ch; cin >> ch; return; } template <class Out> void split(const string& s, Out os) { vector<string> ret; typedef string::size_type string_size; string_size i = 0; // invariant: we have processed characters `['original value of `i', `i)' while (i != s.size()) { // ignore leading blanks // invariant: characters in range `['original `i', current `i)' are all spaces while (i != s.size() && isspace(s[i])) ++i; // find end of next word string_size j = i; // invariant: none of the characters in range `['original `j', current `j)' is a space while (j != s.size() && !isspace(s[j])) ++j; // if we found some nonwhitespace characters if (i != j) { // copy from `s' starting at `i' and taking `j' `\-' `i' chars *os++ = (s.substr(i, j - i)); i = j; } } } // find all the lines that refer to each word in the input map<string, vector<int> > xref(istream& in) // works // now try to pass the template function as an argument to function - what do i put for templated type? //map<string, vector<int> > xref(istream& in, void find_words(vector<string, typedef Out) = split) #LINE 1# { string line; int line_number = 0; map<string, vector<int> > ret; // read the next line while (getline(in, line)) { ++line_number; // break the input line into words vector<string> words; // works // #LINE 2# split(line, back_inserter(words)); // #LINE 3# //find_words(line, back_inserter(words)); // #LINE 4# attempting to use find_words as an argument to function // remember that each word occurs on the current line for (vector<string>::const_iterator it = words.begin(); it != words.end(); ++it) ret[*it].push_back(line_number); } return ret; } int main() { cout << endl << "Enter lines of text, followed by EOF (^Z):" << endl; // call `xref' using `split' by default map<string, vector<int> > ret = xref(cin); // write the results for (map<string, vector<int> >::const_iterator it = ret.begin(); it != ret.end(); ++it) { // write the word cout << it->first << " occurs on line(s): "; // followed by one or more line numbers vector<int>::const_iterator line_it = it->second.begin(); cout << *line_it; // write the first line number ++line_it; // write the rest of the line numbers, if any while (line_it != it->second.end()) { cout << ", " << *line_it; ++line_it; } // write a new line to separate each word from the next cout << endl; } keep_window_open(); return 0; } As you can see, the split function is a template function to handle various types of output iterators as desired. My problem comes when I try to generalize the xref function by passing in the templated split function as an argument. I can't seem to get the type correct. So my question is, can you pass a template function to another function as an argument, and if so, do you have to declare all types before passing it? Or can the compiler infer the types from the way the templated function is used in the body? To demonstrate the errors I get, comment out the existing xref function header, and uncomment the alternate header I'm trying to get working (just below the following commment line.) Also comment the lines tagged LINE 2 and LINE 3 and uncomment LINE 4, which is attempting to use the argument find_words (which defaults to split.) Thanks for any feedback!

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  • parallel java libraries

    - by jetru
    I'm looking for Java libraries/applications which are parallel and feature objects that can be queried in parallel. That is, there is/are objects in which multiple types of operations can be made from different threads and these will be synchronized. It would be helpful if someone could ideas of where I could find such applications as well. EDIT: Actually, language doesn't matter so much, so C++, Python, anything is welcome

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  • Android Google-Shopping API force closes while parsing

    - by Sam Jackson
    I'm trying to send a request to the Google-Shopping API with the following static method which I think is working: public static String GET_TITLE(String url) throws JSONException { InputStream is = null; String result = ""; JSONObject jArray = null; // http post try { HttpClient httpclient = new DefaultHttpClient(); HttpPost httppost = new HttpPost(url); HttpResponse response = httpclient.execute(httppost); HttpEntity entity = response.getEntity(); is = entity.getContent(); } catch(Exception e) { Log.e("log_tag", "Error in http connection "+e.toString()); } The URL I'm passing is this BTW: https://www.googleapis.com/shopping/search/v1/public/products/country=US&q=shirts&alt=json &rankBy=relevancy&key=AIzaSyDRKgGmJrdG6pV6DIg2m-nmIbXydxvpjww Next I try to parse this response (where I think the problem comes in) in the same method: try { jArray = new JSONObject(result); } catch(JSONException e){ Log.e("log_tag", "Error parsing data "+e.toString()); } JSONObject itemObject = jArray.getJSONObject("items"); JSONObject productObject = itemObject.getJSONObject("product"); String attributeGoogleId = productObject.getString("googleId"); String attributeProviderId = productObject.getString("providerId"); String attributeTitle = productObject.getString("title");*/ String attributePrice = productObject.getString("price"); JSONObject popupObject = productObject.getJSONObject("popup"); return attributeTitle; } This has been so frustrating, I know it should be simple but everywhere I look I just can't quite get it to work, I'm not exactly sure what the error is since I'm testing it on my HTC Desire because my emulator gives an 'invalid command-line parameter' error when starting, but that's a different issue, anyway, thanks in advance! EDIT: The first one makes it look like there's a problem with the URL, should I change it and see if it makes a difference? 04-01 12:09:05.142: ERROR/log_tag(24968): Error in http connection java.net.UnknownHostException: www.googleapis.com 04-01 12:09:05.142: ERROR/log_tag(24968): Error converting result java.lang.NullPointerException 04-01 12:09:05.142: ERROR/log_tag(24968): Error parsing data org.json.JSONException: End of input at character 0 of 04-01 12:09:05.142: DEBUG/AndroidRuntime(24968): Shutting down VM 04-01 12:09:05.142: WARN/dalvikvm(24968): threadid=1: thread exiting with uncaught exception (group=0x400259f8) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): FATAL EXCEPTION: main 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=-1, data=Intent { act=com.google.zxing.client.android.SCAN flg=0x80000 (has extras) }} to activity {com.spectrum.stock/com.spectrum.stock.CaptureActivity}: java.lang.NullPointerException 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread.deliverResults(ActivityThread.java:3734) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread.handleSendResult(ActivityThread.java:3776) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread.access$2800(ActivityThread.java:135) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2166) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.os.Handler.dispatchMessage(Handler.java:99) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.os.Looper.loop(Looper.java:144) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread.main(ActivityThread.java:4937) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at java.lang.reflect.Method.invokeNative(Native Method) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at java.lang.reflect.Method.invoke(Method.java:521) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at dalvik.system.NativeStart.main(Native Method) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): Caused by: java.lang.NullPointerException 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at com.spectrum.stock.JSONResponse.GET_TITLE(JSONResponse.java:61) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at com.spectrum.stock.CaptureActivity.onActivityResult(CaptureActivity.java:78) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.Activity.dispatchActivityResult(Activity.java:3931) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): at android.app.ActivityThread.deliverResults(ActivityThread.java:3730) 04-01 12:09:05.152: ERROR/AndroidRuntime(24968): ... 11 more 04-01 12:09:05.162: WARN/ActivityManager(96): Force finishing activity com.spectrum.stock/.CaptureActivity

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  • Do you gain any operations when you constrain a generic type using where T : struct?

    - by Fiona Holder
    This may be a bit of an abstract question, so apologies in advance. I am looking into generics in .NET, and was wondering about the where T : struct constraint. I understand that this allows you to restrict the type used to be a value type. My question is, without any type constraint, you can do a limited number of operations on T. Do you gain the ability to use any additional operations when you specify where T : struct, or is the only value in restricting the types you can pass in?

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  • QValidator for hex input

    - by Evan Teran
    I have a Qt widget which should only accept a hex string as input. It is very simple to restrict the input characters to [0-9A-Fa-f], but I would like to have it display with a delimiter between "bytes" so for example if the delimiter is a space, and the user types 0011223344 I would like the line edit to display 00 11 22 33 44 Now if the user presses the backspace key 3 times, then I want it to display 00 11 22 3. I almost have what i want, so far there is only one subtle bug involving using the delete key to remove a delimiter. Does anyone have a better way to implement this validator? Here's my code so far: class HexStringValidator : public QValidator { public: HexStringValidator(QObject * parent) : QValidator(parent) {} public: virtual void fixup(QString &input) const { QString temp; int index = 0; // every 2 digits insert a space if they didn't explicitly type one Q_FOREACH(QChar ch, input) { if(std::isxdigit(ch.toAscii())) { if(index != 0 && (index & 1) == 0) { temp += ' '; } temp += ch.toUpper(); ++index; } } input = temp; } virtual State validate(QString &input, int &pos) const { if(!input.isEmpty()) { // TODO: can we detect if the char which was JUST deleted // (if any was deleted) was a space? and special case this? // as to not have the bug in this case? const int char_pos = pos - input.left(pos).count(' '); int chars = 0; fixup(input); pos = 0; while(chars != char_pos) { if(input[pos] != ' ') { ++chars; } ++pos; } // favor the right side of a space if(input[pos] == ' ') { ++pos; } } return QValidator::Acceptable; } }; For now this code is functional enough, but I'd love to have it work 100% as expected. Obviously the ideal would be the just separate the display of the hex string from the actual characters stored in the QLineEdit's internal buffer but I have no idea where to start with that and I imagine is a non-trivial undertaking. In essence, I would like to have a Validator which conforms to this regex: "[0-9A-Fa-f]( [0-9A-Fa-f])*" but I don't want the user to ever have to type a space as delimiter. Likewise, when editing what they types, the spaces should be managed implicitly.

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  • Setting property of objects in datacontext

    - by ryudice
    Hi, all my entities have a common property which specifies the company they belong to, I would like to set this property in a method in my datacontext but I do not want to use the partial methods for each of the entity types that the datacontext provides, is there a method that receives any entity that is inserted throught the datacontext so that I can hook to it or override it and set the property using reflection? thanks.

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  • need recommendation for running PHP/Zend based optimizer

    - by senorsmile
    Firstly, I must admit that I don't know much about setting up PHP beyond the basics. I have an Ubuntu 10.04 server system (hosted) running primarily as an FTP store for a commercial store software. The server that the commercial store is installed on is unfortunately not very reliable, and would like to move that to this Ubuntu 10.04 server. (We've already received permission from the store vendor to do this.) My problem is that they use Zend optimizer which is only compatible with PHP 5.2. I have tried a couple of "hacks" to downgrade PHP to 5.2, but it breaks so many other things that it doesn't seem worth it. My idea is to install some sort of container of Ubuntu 8.04 (like OpenVZ) on the server to house a native install of PHP 5.2 to meet the dependency of the store software. However, it appears that OpenVZ is no longer supported on Ubuntu. Is there another solution similar that I could run on a hosted server to installed a separate "container-like" 8.04 system?

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  • Search Form in Responsive Design - Remove Search button on Mobile

    - by Kevin
    I'm working with a search box in the header of a responsive website. On desktop/tablet widths, there's a search input field and a styled 'search' button to the right. You can type in a search term and either click 'SEARCH' button or just hit enter on the keyboard with the same result. When you scale down to mobile widths, the search input field fills the width of the screen. The submit button falls below it. On a desktop, clicking the button or hitting enter activate the search. On an actual iphone phone, you can hit the 'SEARCH' button, but the native mobile keyboard that rises from the bottom of the screen has a search button where the enter/return key would normally be. It seems to know I'm in a form and the keyboard automatically gives me the option to kick off the search by basically hitting the ENTER key location....but it says SEARCH. So far so good. I figure I don't need the button in the header on mobile since it's already in the keyboard. Therefore, I'll hide the button on mobile widths and everything will be tighter and look better. So I added this to my CSS to hide it in mobile: #search-button {display: none;} But now the search doesn't work at all. On mobile, I don't get the option in the keyboard that showed up before and if I just hit enter, it doesn't work at all. On desktop at mobile width, hitting enter also not longer works. So clearly by hiding the submit/search button, the phone no longer gave me the native option to run the search. In addition, on the desktop at mobile width, even hitting enter inside the search input box also fails to launch the the search. Here's my search box: <form id="search-form" method="get" accept-charset="UTF-8, utf-8" action="search.php"> <fieldset> <div id="search-wrapper"> <label id="search-label" for="search">Item:</label> <input id="search" class="placeholder-color" name="item" type="text" placeholder="Item Number or Description" /> <button id="search-button" title="Go" type="submit"><span class="search-icon"></span></button> </div> </fieldset> </form> Here's what my CSS looks like: #search-wrapper { float: left; display: inline-block; position: relative; white-space: nowrap; } #search-button { display: inline-block; cursor: pointer; vertical-align: top; height: 30px; width: 40px; } @media only screen and (max-width: 639px) { #search-wrapper { display: block; margin-bottom: 7px; } #search-button { /* this didn't work....it hid the button but the search failed to load */ display: none;*/ } } So.....how can I hide this submit button when I'm on a mobile screen, but still let the search run from the mobile keyboard or just run by hitting enter when in the search input box. I was sure that putting display:none on the search button at mobile width would do the trick, but apparently not. Thanks...

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  • Best LXDE based distro/distro that supports LXDE?

    - by Misha Koshelev
    Lubuntu is nice - but it seems the LXDE version is not as up to date as Fedora LXDE Spin or even Debian squeeze with LXDE installed... I do like Chromium on Lubuntu though... its faster and a nice touch. So, any good recommendations? I am fairly used to Ubuntu and the dpkg/apt commands, but am willing to learn. I am looking for a lightweight 64-bit distribution for my main laptop (it is by no means "old" or "low spec" but I like that Lubuntu starts up in like 2 secs). Anyway as you can see I have a strong Lubuntu bias, but there are issues like: LXDE version seems not to be recent (esp in 10.04 version which seems to work more stably for me - with Nvidia drivers etc) 64 bit install is currently a pain - requires first install of minimal CD or alternate CD both of which required wired Ethernet, then install of lubuntu from PPA. Native 64-bit support would be nice. Linux Mint LXDE, for example, is also only 32-bit. Thank you so much

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  • Rating mechanisms

    - by Jasie
    Is there any place that showcases a bunch of different types of rating systems (like using multiple sliders, star ratings, up/down votes)? I'm trying to get ideas for a better rating system than just up/down (more criteria). (I'm not interested in the backend, but the human/computer interaction part of it).

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  • Languages and VMs: Features that are hard to optimize and why

    - by mrjoltcola
    I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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  • Object serialization practical uses?

    - by nash
    How many software projects have you worked on used object serialization? I personally never came across a scenario where object serialization was used. One use case i can think of is, a server software storing objects to disk to save memory. Are there other types of software where object serialization is essential or preferred over a database?

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