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  • How to make safe cast using generics in C#?

    - by TN
    I want to implement a generic method on a generic class which would allow to cast safely, see example: public class Foo<T> : IEnumerable<T> { ... public IEnumerable<R> SafeCast<R>() where T : R { return this.Select(item => (R)item); } } However, the compiler tells me that Foo<T>.SafeCast<R>() does not define parameter 'T'. I understand this message that I cannot specify a constraint on T in the method since it is not defined in the method. But how can I specify an inverse constraint?

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  • Maven 2.1.0 not passing on system properties to Java virtual machine

    - by raisercostin
    We use the command line to pass on system properties to the Java virtual machine when running our Hudson builds on a Linux box. It used to work quite well in 2.0.9 by since we upgraded to 2.1.0 it has stopped working altogether. The system properties just never make it to the Java virtual machine. I have created a small test project and indeed it does not work at all. I have attached it in case you want to give it a go. This should work just fine with Maven 2.0.9: mvn2.0.9 -Dsystem.test.property=test test But this will fail: mvn2.1 -Dsystem.test.property=test test The Java code simply does this assertTrue( System.getProperty("system.test.property") != null); , Apr 20, 2009; 12:44pm edward eric pedersson

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  • System Slow After Uprading Ubuntu

    - by Aragon N
    i have an ubuntu network machine which has release of 10.04.1 LTS Lucid. on this system i have apache, postgresql and django. for some app. development i have to install php and php-curl... due to being on network, i have exported wmvare machine to internet and firstly i have upgraded system and then install php5 packages on it. After all replacing it with its old place, i have considered that the new system query is some slow according to another. Old system query time : 140 ms New system query time : 9.11 s i have checked /etc/network interface and it seems there is no problem. i have checked /etc/resolv.conf and it seems ok i have checked /etc/nsswitch.conf and only host section is different from old one which old system has hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4 and then i have checked time host -t A services.myapp.com and i got real 0m0.355s user 0m0.010s sys 0m0.020s and now what can i have to check for boosting my system as before?

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  • Download office document without the web server trying to render it

    - by Dan Revell
    I'm trying to download an InfoPath template that's hosted on SharePoint. If I hit the url in internet explorer it asks me where to save it and I get the correct file on my disk. If I try to do this programmatically with WebClient or HttpWebRequest then I get HTML back instead. How can I make my request so that the web server returns the actual xsn file and doesn't try to render it in html. If internet explorer can do this then it's logical to think that I can too. I've tried setting the Accept property of the request to application/x-microsoft-InfoPathFormTemplate but that hasn't helped. It was a shot in the dark.

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  • What are the system requirements for each flavor of Ubuntu Desktop?

    - by Braiam
    I'm thinking about installing Ubuntu Desktop, but I don't know what flavor is the better for my system. What are the minimum and recommended hardware requirements? What kind of CPU? How much memory? Should I have Hardware Acceleration? What flavor should I use? This is an attempt of a canonical answer. My answers have the "official minimal requirements", the recommended are a mix of official sources and opinion based (along with the answer it's told the source). You can comment or edit if you feel that the information is obsolete or incomplete. Is a good rule of thumb that any system capable to run Windows Vista, 7, 8 x86 OS X will almost always be a lot faster with any Ubuntu flavor even if they are lower-spec than described below.

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  • Will there ever be a version of Java which does not perform Type Erasure

    - by user63904
    Type erasure enables Java applications that use generics to maintain binary compatibility with Java libraries and applications that were created before generics Generics were introduced in Java 1.5, so presumably the statement "applications that were created before generics" is referring to Java 1.4? Given that Java 1.4 entered its End Of Life around 2006 and was officially End Of Life'd around 2008. Why is type erasure still being performed in Java 7, etc... Has the statement now become self referential i.e. Type erasure enables Java applications that use generics to maintain binary compatibility with Java libraries and applications that were created with Java versions that perform Type Erasure. Meaning therefore that there will never be a version of Java that doesn't perform Type Erasure.

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  • Is there a way of leveling/compressing the sound system-wide?

    - by JethroDawnfine
    As a Laptop user, I'm sure that a lot of people, even the ones using Netbooks would have already gone through this problem. Especially when listening to podcasts, and using it as an example, the sound might have loud moments and quiet moments, one person speaking loud and the other speaking very quiet in the same episode. Thereby, I always wanted the sound to be compressed system-wide, and I just noted the other day, that in Windows, some Realtek drivers already offer this function. We have already a pulseaudio plugin for equalization system-wide, and although it still has problems like not letting us change its values and listen the change in real time, or cracking the sound while changing pulse volume, I do love it and use it. Now I'm just missing something to keep the sound around 0db (or near the volume level you're using) as a leveler plugin for pulseaudio. Any suggestion?

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  • Why subtract a value from itself (x - x) in Python?

    - by endolith
    In NumPy functions, there are often initial lines that do checking of variable types, forcing them to be certain types, etc. Can someone explain the point of these lines? What does subtracting a value from itself do? t,w = asarray(t), asarray(duty) w = asarray(w + (t-t)) t = asarray(t + (w-w))

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  • Dynamic Code for type casting Generic Types 'generically' in C#

    - by Rick Strahl
    C# is a strongly typed language and while that's a fundamental feature of the language there are more and more situations where dynamic types make a lot of sense. I've written quite a bit about how I use dynamic for creating new type extensions: Dynamic Types and DynamicObject References in C# Creating a dynamic, extensible C# Expando Object Creating a dynamic DataReader for dynamic Property Access Today I want to point out an example of a much simpler usage for dynamic that I use occasionally to get around potential static typing issues in C# code especially those concerning generic types. TypeCasting Generics Generic types have been around since .NET 2.0 I've run into a number of situations in the past - especially with generic types that don't implement specific interfaces that can be cast to - where I've been unable to properly cast an object when it's passed to a method or assigned to a property. Granted often this can be a sign of bad design, but in at least some situations the code that needs to be integrated is not under my control so I have to make due with what's available or the parent object is too complex or intermingled to be easily refactored to a new usage scenario. Here's an example that I ran into in my own RazorHosting library - so I have really no excuse, but I also don't see another clean way around it in this case. A Generic Example Imagine I've implemented a generic type like this: public class RazorEngine<TBaseTemplateType> where TBaseTemplateType : RazorTemplateBase, new() You can now happily instantiate new generic versions of this type with custom template bases or even a non-generic version which is implemented like this: public class RazorEngine : RazorEngine<RazorTemplateBase> { public RazorEngine() : base() { } } To instantiate one: var engine = new RazorEngine<MyCustomRazorTemplate>(); Now imagine that the template class receives a reference to the engine when it's instantiated. This code is fired as part of the Engine pipeline when it gets ready to execute the template. It instantiates the template and assigns itself to the template: var template = new TBaseTemplateType() { Engine = this } The problem here is that possibly many variations of RazorEngine<T> can be passed. I can have RazorTemplateBase, RazorFolderHostTemplateBase, CustomRazorTemplateBase etc. as generic parameters and the Engine property has to reflect that somehow. So, how would I cast that? My first inclination was to use an interface on the engine class and then cast to the interface.  Generally that works, but unfortunately here the engine class is generic and has a few members that require the template type in the member signatures. So while I certainly can implement an interface: public interface IRazorEngine<TBaseTemplateType> it doesn't really help for passing this generically templated object to the template class - I still can't cast it if multiple differently typed versions of the generic type could be passed. I have the exact same issue in that I can't specify a 'generic' generic parameter, since there's no underlying base type that's common. In light of this I decided on using object and the following syntax for the property (and the same would be true for a method parameter): public class RazorTemplateBase :MarshalByRefObject,IDisposable { public object Engine {get;set; } } Now because the Engine property is a non-typed object, when I need to do something with this value, I still have no way to cast it explicitly. What I really would need is: public RazorEngine<> Engine { get; set; } but that's not possible. Dynamic to the Rescue Luckily with the dynamic type this sort of thing can be mitigated fairly easily. For example here's a method that uses the Engine property and uses the well known class interface by simply casting the plain object reference to dynamic and then firing away on the properties and methods of the base template class that are common to all templates:/// <summary> /// Allows rendering a dynamic template from a string template /// passing in a model. This is like rendering a partial /// but providing the input as a /// </summary> public virtual string RenderTemplate(string template,object model) { if (template == null) return string.Empty; // if there's no template markup if(!template.Contains("@")) return template; // use dynamic to get around generic type casting dynamic engine = Engine; string result = engine.RenderTemplate(template, model); if (result == null) throw new ApplicationException("RenderTemplate failed: " + engine.ErrorMessage); return result; } Prior to .NET 4.0  I would have had to use Reflection for this sort of thing which would have a been a heck of a lot more verbose, but dynamic makes this so much easier and cleaner and in this case at least the overhead is negliable since it's a single dynamic operation on an otherwise very complex operation call. Dynamic as  a Bailout Sometimes this sort of thing often reeks of a design flaw, and I agree that in hindsight this could have been designed differently. But as is often the case this particular scenario wasn't planned for originally and removing the generic signatures from the base type would break a ton of other code in the framework. Given the existing fairly complex engine design, refactoring an interface to remove generic types just to make this particular code work would have been overkill. Instead dynamic provides a nice and simple and relatively clean solution. Now if there were many other places where this occurs I would probably consider reworking the code to make this cleaner but given this isolated instance and relatively low profile operation use of dynamic seems a valid choice for me. This solution really works anywhere where you might end up with an inheritance structure that doesn't have a common base or interface that is sufficient. In the example above I know what I'm getting but there's no common base type that I can cast to. All that said, it's a good idea to think about use of dynamic before you rush in. In many situations there are alternatives that can still work with static typing. Dynamic definitely has some overhead compared to direct static access of objects, so if possible we should definitely stick to static typing. In the example above the application already uses dynamics extensively for dynamic page page templating and passing models around so introducing dynamics here has very little additional overhead. The operation itself also fires of a fairly resource heavy operation where the overhead of a couple of dynamic member accesses are not a performance issue. So, what's your experience with dynamic as a bailout mechanism? © Rick Strahl, West Wind Technologies, 2005-2012Posted in CSharp   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Swap not available on System Monitor

    - by Zaki
    I had a swap partition of 1GB (RAM 1GB, Ubuntu 12.04 lts). Now swap is not shown on System Monitor neither can I hibernate my pc (sudo pm-hibernate). blkid output: /dev/sda1: UUID="B8B4FBB1B4FB706C" TYPE="ntfs" /dev/sda2: UUID="2ea7d608-2d89-4e41-9436-d05cb3ce8871" TYPE="swap" /dev/sda3: UUID="3219d03a-67e4-454b-8ce7-a27831846e35" TYPE="ext4" /dev/sda5: LABEL="Softwares" UUID="AC1CC3301CC2F47C" TYPE="ntfs" /dev/sda6: LABEL="Education" UUID="1E103E6C103E4B53" TYPE="ntfs" /dev/sda7: LABEL="Recreation" UUID="2CC8D181C8D149AA" TYPE="ntfs" /dev/sda8: LABEL="Miscellaneous" UUID="0274D6B174D6A727" TYPE="ntfs" /etc/fstab # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc nodev,noexec,nosuid 0 0 # / was on /dev/sda6 during installation UUID=3219d03a-67e4-454b-8ce7-a27831846e35 / ext4 errors=remount-ro 0 1 # swap was on /dev/sda5 during installation UUID=2ea7d608-2d89-4e41-9436-d05cb3ce8871 none swap sw 0 0 free -m total used free shared buffers cached Mem: 991 867 123 0 27 418 -/+ buffers/cache: 421 569 Swap: 0 0 0 cat /proc/swaps Filename Type Size Used Priority fdisk -l Disk /dev/sda: 160.0 GB, 160041885696 bytes 255 heads, 63 sectors/track, 19457 cylinders, total 312581808 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x9f369f36 Device Boot Start End Blocks Id System /dev/sda1 * 63 31471334 15735636 7 HPFS/NTFS/exFAT /dev/sda2 31471616 33470447 999416 82 Linux swap / Solaris /dev/sda3 33472512 62539775 14533632 83 Linux /dev/sda4 62541045 312592769 125025862+ f W95 Ext'd (LBA) /dev/sda5 62541108 125066024 31262458+ 7 HPFS/NTFS/exFAT /dev/sda6 125066088 187591004 31262458+ 7 HPFS/NTFS/exFAT /dev/sda7 187591068 250115984 31262458+ 7 HPFS/NTFS/exFAT /dev/sda8 250116048 312576704 31230328+ 7 HPFS/NTFS/exFAT swapon --all swapon: /dev/sda2: swapon failed: Invalid argument dmesg | grep -A 5 -B 5 -i swap [ 9.487404] EXT4-fs (sda3): ext4_orphan_cleanup: deleting unreferenced inode 131645 [ 9.487413] EXT4-fs (sda3): ext4_orphan_cleanup: deleting unreferenced inode 131330 [ 9.487418] EXT4-fs (sda3): 16 orphan inodes deleted [ 9.487420] EXT4-fs (sda3): recovery complete [ 9.578600] EXT4-fs (sda3): mounted filesystem with ordered data mode. Opts: (null) [ 20.580539] Swap area shorter than signature indicates [ 20.588363] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready [ 20.619443] udevd[330]: starting version 175 [ 20.649959] lp: driver loaded but no devices found [ 20.662972] [drm] Initialized drm 1.1.0 20060810 [ 20.675515] i915 0000:00:02.0: setting latency timer to 64 -- [ 72.288573] PM: thaw of drv:sr dev:3:0:0:0 complete after 178.143 msecs [ 72.288578] PM: thaw of drv:scsi_device dev:3:0:0:0 complete after 178.136 msecs [ 72.299677] PM: thaw of drv:scsi_device dev:2:0:0:0 complete after 189.270 msecs [ 72.309473] PM: thaw of devices complete after 202.763 msecs [ 72.309668] PM: writing image. [ 72.309670] PM: Cannot find swap device, try swapon -a. [ 72.309699] PM: Cannot get swap writer [ 72.329896] Restarting tasks ... done. [ 72.331777] PM: Basic memory bitmaps freed [ 72.331792] video LNXVIDEO:00: Restoring backlight state [ 72.420048] option1 ttyUSB0: option_instat_callback: error -84 [ 72.804047] option1 ttyUSB0: option_instat_callback: error -84 -- [ 145.960625] sd 7:0:0:0: Attached scsi generic sg2 type 0 [ 145.972036] sd 7:0:0:0: [sdb] Attached SCSI removable disk [ 172.430508] PPP BSD Compression module registered [ 172.455583] PPP Deflate Compression module registered [ 332.260789] type=1400 audit(1381814763.342:27): apparmor="DENIED" operation="capable" parent=1 profile="/usr/sbin/cupsd" pid=636 comm="cupsd" pid=636 comm="cupsd" capability=36 capname="block_suspend" [ 1913.030998] Swap area shorter than signature indicates [ 2022.530155] type=1400 audit(1381816453.610:28): apparmor="DENIED" operation="capable" parent=1 profile="/usr/sbin/cupsd" pid=636 comm="cupsd" pid=636 comm="cupsd" capability=36 capname="block_suspend" [ 4062.729509] Swap area shorter than signature indicates Please help. Thanks in advance. df -h Filesystem Size Used Avail Use% Mounted on /dev/sda3 14G 6.1G 7.0G 47% / udev 488M 4.0K 488M 1% /dev tmpfs 199M 868K 198M 1% /run none 5.0M 4.0K 5.0M 1% /run/lock none 496M 224K 496M 1% /run/shm

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  • Postfix : error: unsupported dictionary type: mysql

    - by flavio.troja
    I've a problem w/ postfix problem: # tail -f /var/log/mail.err Aug 20 17:57:50 myserver postfix/smtpd[8243]: error: unsupported dictionary type: mysql Aug 20 17:57:50 myserver postfix/smtpd[8243]: error: unsupported dictionary type: mysql Aug 20 17:58:05 myserver postfix/smtpd[8244]: error: unsupported dictionary type: mysql Aug 20 17:58:05 myserver postfix/smtpd[8244]: error: unsupported dictionary type: mysql Aug 20 18:00:38 myserver postfix/smtpd[8277]: error: unsupported dictionary type: mysql Aug 20 18:00:38 myserver postfix/smtpd[8277]: error: unsupported dictionary type: mysql Aug 20 18:03:32 myserver postfix/smtpd[8320]: error: unsupported dictionary type: mysql Aug 20 18:03:32 myserver postfix/smtpd[8320]: error: unsupported dictionary type: mysql Aug 20 18:03:33 myserver postfix/trivial-rewrite[8322]: error: unsupported dictionary type: mysql Aug 20 18:03:33 myserver postfix/trivial-rewrite[8322]: error: unsupported dictionary type: mysql idea?

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  • System freezes during boot process

    - by slugster
    Hi everyone, i have a machine running Win7 Ultimate. It was running fine, then it just froze - all the stuff i was doing was still on the screen, but mouse and keyboard input was ignored, any animation that was happening on the screen stopped, the machine literally just froze. So i rebooted (power off button), from then on the machine will reboot, but it ultimately freezes again. The instance when this happens will vary - i have made it as far as the Windows login screen, but mostly it will do the POST, then give me the option to press F1 to continue or Del to enter BIOS settings (but of course pressing a key has no effect - it's frozen!). I have disconnected everything not necessary for the boot process, the only peripheral that remains attached is the keyboard. (even the network cable is disconnected). Prior to this the machine was operating fine. The install of Win7 is only 2 days old, and it was a fresh reinstall (i.e. not an upgrade or repair). Can anyone give me an indication of what may be wrong here? I'm not sure if this question should be here or on SuperUser, please migrate it if i have chosen the wrong board.

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  • Which hardware changes require operating system reinstallation?

    - by Mark
    I'm about to upgrade my computer but might keep some parts. Just wandering what I would have to keep to prevent me having to reinstall my OSs, at the moment I have a dual boot setup with ubuntu and windows 7. I'm pretty sure you can't just take your hard drive with the OS on it and put it into a different box and keep going (can you?) but I know you can change the graphics cards, secondary hard drives and ram with out a problem. So what is it that you can't change? The CPU? Motherboard? Thanks for any replies

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  • System freezes during boot process

    - by slugster
    Hi everyone, i have a machine running Win7 Ultimate. It was running fine, then it just froze - all the stuff i was doing was still on the screen, but mouse and keyboard input was ignored, any animation that was happening on the screen stopped, the machine literally just froze. So i rebooted (power off button), from then on the machine will reboot, but it ultimately freezes again. The instance when this happens will vary - i have made it as far as the Windows login screen, but mostly it will do the POST, then give me the option to press F1 to continue or Del to enter BIOS settings (but of course pressing a key has no effect - it's frozen!). I have disconnected everything not necessary for the boot process, the only peripheral that remains attached is the keyboard. (even the network cable is disconnected). Prior to this the machine was operating fine. The install of Win7 is only 2 days old, and it was a fresh reinstall (i.e. not an upgrade or repair). Can anyone give me an indication of what may be wrong here? I'm not sure if this question should be here or on SuperUser, please migrate it if i have chosen the wrong board.

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  • How to get partition information from non-booting server?

    - by gravyface
    Need to manually rebuild a mirrored array on a server and am in the process of reinstalling SBS 2003 on it. However, it's a Dell server, and know that there's the Dell FAT32 diagnostics partition, a system partition, and a data partition, but do not know the size of each. Planning on reinstalling SBS 2003, all applications on the server, and then doing a System State restore, but figured that not having the correct partitions will cause some grief: am I right? Almost thinking that the size of the partitions shouldn't matter, but not positive. Question: should I care about the size of the partition? If so, how can I get this partition information from a non-booting drive? We have an Acronis image of the one working disk and the partitions are mounted/viewable in Explorer on a workstation, but I'm not sure where the Logical Disk Manager/Disk Management data is stored and/or if there's a way to retrieve it without having a working Windows installation.

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  • What is the difference between sar -B verses sar -W

    - by Mark
    I am trying to understand why my system is running slowly. I found the sar command, but wanted to know the difference between sar -B and sar -W I read the man page, and I understand that -B gives me the paging statistics and -W gives me the swapping statistics. What I would like to understand is the following: What is the correlation between the two sets of statistics. When should I be concerned about -B and when about -W? ie, what values from each command should I be concerned with? Which statistic is more closely related to system performance Thanks

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