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  • How to detect if collection contain instance of specific type?

    - by KentZhou
    Suppose I create collection like Collection<IMyType> coll; Then I have many implelentations of IMyTypem like, T1, T2, T3... Then I want know if the collection coll contains a instance of type T1. So I want to write a method like public bool ContainType( <T>){...} here the param should be class type, not class instance. How to write code for this kind of issue?

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  • What is the correct way to create a single instance application?

    - by Nidonocu
    Using C# and WPF under .net (rather than WindowsForms or console), what is the correct way to create an application that can only be run as a single instance? I know it has something to do with some mythical thing called a mutex, rarely can I find someone that bothers to stop and explain what one of these are. The code needs to also inform the already running instance that the user tried to start a second one, and maybe also pass any command line arguments if any existed.

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  • Is it a good or bad practice to call instance methods from a java constructor?

    - by Steve
    There are several different ways I can initialize complex objects (with injected dependencies and required set-up of injected members), are all seem reasonable, but have various advantages and disadvantages. I'll give a concrete example: final class MyClass { private final Dependency dependency; @Inject public MyClass(Dependency dependency) { this.dependency = dependency; dependency.addHandler(new Handler() { @Override void handle(int foo) { MyClass.this.doSomething(foo); } }); doSomething(0); } private void doSomething(int foo) { dependency.doSomethingElse(foo+1); } } As you can see, the constructor does 3 things, including calling an instance method. I've been told that calling instance methods from a constructor is unsafe because it circumvents the compiler's checks for uninitialized members. I.e. I could have called doSomething(0) before setting this.dependency, which would have compiled but not worked. What is the best way to refactor this? Make doSomething static and pass in the dependency explicitly? In my actual case I have three instance methods and three member fields that all depend on one another, so this seems like a lot of extra boilerplate to make all three of these static. Move the addHandler and doSomething into an @Inject public void init() method. While use with Guice will be transparent, it requires any manual construction to be sure to call init() or else the object won't be fully-functional if someone forgets. Also, this exposes more of the API, both of which seem like bad ideas. Wrap a nested class to keep the dependency to make sure it behaves properly without exposing additional API:class DependencyManager { private final Dependency dependency; public DependecyManager(Dependency dependency) { ... } public doSomething(int foo) { ... } } @Inject public MyClass(Dependency dependency) { DependencyManager manager = new DependencyManager(dependency); manager.doSomething(0); } This pulls instance methods out of all constructors, but generates an extra layer of classes, and when I already had inner and anonymous classes (e.g. that handler) it can become confusing - when I tried this I was told to move the DependencyManager to a separate file, which is also distasteful because it's now multiple files to do a single thing. So what is the preferred way to deal with this sort of situation?

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  • Would the instance reference parameters passed into the static methods get garbage collected?

    - by 123Developer
    I know that the static objects in .Net managed world are loaded in Loader Heap which is never going to be garbage collected. What happens to the instance reference parameters passed to a static methods. Are they get garbage collected once the static function executed completely Or they are going to live forever as those instance reference variables are once passed to static method? I am really confused this evening; Please guide me. Thanks and regards 123Developer.

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  • C# Reflection: How to call method of interface without creating instance?

    - by jitm
    Hello, I have situation where I have to call method of interface using reflection, like this object x = null; MethodInfo method = interfaceExists.GetMethod("ShutDown"); method.Invoke(x, new object[] { 4 }) As you can see I do not create instance of object! And, as I can supposed, I receive exception Non-static method requires a target And Question, Can I call method of interface using reflection without creating instance of interface and if YES, How I can do it ? Thank you.

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  • How to see if type is instance of a class in Haskell?

    - by Raekye
    I'm probably doing this completely wrong (the unhaskell way); I'm just learning so please let me know if there's a better way to approach this. Context: I'm writing a bunch of tree structures. I want to reuse my prettyprint function for binary trees. Not all trees can use the generic Node/Branch data type though; different trees need different extra data. So to reuse the prettyprint function I thought of creating a class different trees would be instances of: class GenericBinaryTree a where is_leaf :: a -> Bool left :: a -> a node :: a -> b right :: a -> a This way they only have to implement methods to retrieve the left, right, and current node value, and prettyprint doesn't need to know about the internal structure. Then I get down to here: prettyprint_helper :: GenericBinaryTree a => a -> [String] prettyprint_helper tree | is_leaf tree = [] | otherwise = ("{" ++ (show (node tree)) ++ "}") : (prettyprint_subtree (left tree) (right tree)) where prettyprint_subtree left right = ((pad "+- " "| ") (prettyprint_helper right)) ++ ((pad "`- " " ") (prettyprint_helper left)) pad first rest = zipWith (++) (first : repeat rest) And I get the Ambiguous type variable 'a0' in the constraint: (Show a0) arising from a use of 'show' error for (show (node tree)) Here's an example of the most basic tree data type and instance definition (my other trees have other fields but they're irrelevant to the generic prettyprint function) data Tree a = Branch (Tree a) a (Tree a) | Leaf instance GenericBinaryTree (Tree a) where is_leaf Leaf = True is_leaf _ = False left (Branch left node right) = left right (Branch left node right) = right node (Branch left node right) = node I could have defined node :: a -> [String] and deal with the stringification in each instance/type of tree, but this feels neater. In terms of prettyprint, I only need a string representation, but if I add other generic binary tree functions later I may want the actual values. So how can I write this to work whether the node value is an instance of Show or not? Or what other way should I be approaching this problem? In an object oriented language I could easily check whether a class implements something, or if an object has a method. I can't use something like prettyprint :: Show a => a -> String Because it's not the tree that needs to be showable, it's the value inside the tree (returned by function node) that needs to be showable. I also tried changing node to Show b => a -> b without luck (and a bunch of other type class/preconditions/whatever/I don't even know what I'm doing anymore).

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  • How to rename multiple files by replacing word in file name geting from the shell script variables?

    - by fy6877
    This question like this thread. How to rename multiple files by replacing word in file name? My example is more complex than the above topic. The two variables are $name and $ newname getting from the shell script other location. $name and $ newname may have the unicode words or special symbles like []<?...etc,so could anyone help me to provide a method to add a part of script in shell scrit to solve file name replacing question. BTW,I try to type two kind of commands to change the part of file name, but it can't work. rename.ul '$name' '$newname' /home/fy6877/test/final/* ls /home/fy6877/test/final/|xargs -I$ rename.ul '$name' '$newname' $

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  • Is it possible to have environment variables in the path of the working directory : PS1?

    - by mthpvg
    I am on Lubuntu and I am using bash. My PS1 (in .bashrc) is : PS1="\w> " I like it because I need to paste the working directory all the time. The problem is that the path is always very long and since I use terminator I only have half of my screen's width available to display it... it is ugly and annoying. My command prompt looks like that : /this/is/a/very/long/path/that/i/want/to/make/shorter > I'd like to set in my environment variables : $tiavl=/this/is/a/very/long And then I'll get : $tiavl/path/that/i/want/to/make/shorter > The goal is to have something shorter in the command prompt but I still want to be able to copy paste it and do : cd $tiavl/path/that/i/want/to/make/shorter It is a bit like with $HOME : ~/path/that/i/want/to/make/shorter > I know where I am and I can copy paste the ~. Thanks.

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  • How to upload stuff to Amazon EC2 Windows instance?

    - by JohnIdol
    I've never used Amazon EC2 - I am thinking to test a few instances for running intensive computation processes I have a requirement for rather than buying real hardware. I am given to understand the thing is quite easy to setup - but I have no clue of how it actually works, in terms of transferring data to my ec2 instances. So the question is how can I upload stuff to my instance? Any help appreciated!

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  • Why is my concurrency capacity so low for my web app on a LAMP EC2 instance?

    - by AMF
    I come from a web developer background and have been humming along building my PHP app, using the CakePHP framework. The problem arose when I began the ab (Apache Bench) testing on the Amazon EC2 instance in which the app resides. I'm getting pretty horrendous average page load times, even though I'm running a c1.medium instance (2 cores, 2GB RAM), and I think I'm doing everything right. I would run: ab -n 200 -c 20 http://localhost/heavy-but-view-cached-page.php Here are the results: Concurrency Level: 20 Time taken for tests: 48.197 seconds Complete requests: 200 Failed requests: 0 Write errors: 0 Total transferred: 392111200 bytes HTML transferred: 392047600 bytes Requests per second: 4.15 [#/sec] (mean) Time per request: 4819.723 [ms] (mean) Time per request: 240.986 [ms] (mean, across all concurrent requests) Transfer rate: 7944.88 [Kbytes/sec] received While the ab test is running, I run VMStat, which shows that Swap stays at 0, CPU is constantly at 80-100% (although I'm not sure I can trust this on a VM), RAM utilization ramps up to about 1.6G (leaving 400M free). Load goes up to about 8 and site slows to a crawl. Here's what I think I'm doing right on the code side: In Chrome browser uncached pages typically load in 800-1000ms, and cached pages load in 300-500ms. Not stunning, but not terrible either. Thanks to view caching, there might be at most one DB query per page-load to write session data. So we can rule out a DB bottleneck. I have APC on. I am using Memcached to serve the view cache and other site caches. xhprof code profiler shows that cached pages take up 10MB-40MB in memory and 100ms - 1000ms in wall time. Pages that would be the worst offenders would look something like this in xhprof: Total Incl. Wall Time (microsec): 330,143 microsecs Total Incl. CPU (microsecs): 320,019 microsecs Total Incl. MemUse (bytes): 36,786,192 bytes Total Incl. PeakMemUse (bytes): 46,667,008 bytes Number of Function Calls: 5,195 My Apache config: KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 3 <IfModule mpm_prefork_module> StartServers 5 MinSpareServers 5 MaxSpareServers 10 MaxClients 120 MaxRequestsPerChild 1000 </IfModule> Is there something wrong with the server? Some gotcha with the EC2? Or is it my code? Some obvious setting I should look into? Too many DNS lookups? What am I missing? I really want to get to 1,000 concurrency capacity, but at this rate, it ain't gonna happen.

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  • Why do I get "Only a single instance of this application can run" ?

    - by Kathleen
    I have been trying to update my Adobe Flash Player for hours. I've read the forum, downloaded the uninstaller, restarted on every attempt. Tried for Firefox and IE. When I click on the downloaded icon, it disappears and this message comes up: "only one instance of this application can run". Also checked Adobe and other various sites for a solution. I need my browsers, with Flash. Can someone help?

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  • WPF: How can I KEEP the same ItemTemplate instance once its created ??

    - by Samir Sabri
    Hello, Here is a cinario: I have a ListView, with ItemsSource = ProjectModel.Instance.PagesModelsCollection; where PagesModelsCollection is an ObservableCollection In the ListView XAML part: <ListView.ItemTemplate> <DataTemplate x:Name="PagesViewDataTemplate"> <DataTemplate.Resources> <Style x:Key="PageHostStyle" TargetType="{x:Type p:KPage}"> </Style> </DataTemplate.Resources> <StackPanel x:Name="MarginStack" Margin="50,50,50,50" > <p:KPage x:Name="PageHost" > </p:KPage> </StackPanel> </DataTemplate> </ListView.ItemTemplate> The problem is the ITemTemplate is re-created each time we refresh the Items. So, if we have 100 Item in the list view, another 100 new ItemTemplate instance will be created if we refresh the items! As a result, if we add UIElements on one of the ItemTemplate intances, those added UIElements will be lost, because the old ITemTemplate is replaced with a new one! How can I KEEP the ItemTemplate instance once its created ??

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  • How do I convert an AMD module from a singleton to an instance?

    - by Jamie Ide
    I'm trying to convert a working Durandal view model module from a singleton to an instance. The original working version followed this pattern: define(['knockout'], function(ko) { var vm = { activate: activate, companyId: null; company: ko.observable({}) }; return vm; function activate(companyId) { vm.companyId = companyId; //get company data then vm.company(data); } } The new version exports a function so that I get a new instance on every request... define(['knockout'], function(ko) { var vm = function() { activate = activate; companyId = null; company = ko.observable({}); }; return vm; function activate(companyId) { vm.companyId = companyId; //get company data then vm.company(data); } } The error I'm getting is "object function () [...function signature...] has no method company on the line vm.company(data);. What am I doing wrong? Why can I set the property but can't access the knockout observable? How should I refactor the original code so that I get a new instance on every request? My efforts to simplify the code for this question hid the actual problem. My real code was using Q promises and calling two methods with Q.All. Since Q is in the global namespace, it couldn't resolve my viewmodel after converting to a function. Passing the view model to the methods called by Q resolved the problem.

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  • Type classe, generic memoization

    - by nicolas
    Something quite odd is happening with y types and I quite dont understand if this is justified or not. I would tend to think not. This code works fine : type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, obj>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res And this ones complains type DictionarySingleton private () = static let mutable instance = Dictionary<string*obj, _>() static member Instance = instance let memoize (f:'a -> 'b) = fun (x:'a) -> let key = f.ToString(), (x :> obj) if (DictionarySingleton.Instance).ContainsKey(key) then let r = (DictionarySingleton.Instance).[key] r :?> 'b else let res = f x (DictionarySingleton.Instance).[key] <- (res :> obj) res The difference is only the underscore in the dictionary definition. The infered types are the same, but the dynamic cast from r to type 'b exhibits an error. 'this runtime coercition ... runtime type tests are not allowed on some types, etc..' Am I missing something or is it a rough edge ?

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