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• What trick does Java use to avoid spaces in >> ?

  - by kunjaan

  In the Java Generic Book, while contrasting the difference between C++ Templates and Java Generic says: In C++, a problem arises because without the space denotes the right-shift operator. Java fixes the problem by a trick in the grammar.) What is this trick?

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• using generic and for each loop in jsp

  - by mawia

  I am developing a web application. I am using Eclipse as IDE. I was using generic and for each loop, both being feature of java 1.5, and it compiled quite fine when used in backend means in simple java classes. But when I'm using these on jsp, jsp is failing to compile with error showing generic and for each as culprit. Can you shed some light on this? Maybe I am at fault with Eclipse settings?

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• Changing the Order in a .NET Generic Dictionary

  - by pm_2

  I have a class that inherits from a generic dictionary as follows: Class myClass : System.Collections.Generic.Dictionary<int, Object> I have added a list of values to this in a particular order, but I now wish to change that order. Is there any way (without removing and re-adding) that I could effectively re-index the values; so change the object at index 1 to now be at index 10 for example? For example, this doesn't work: myClass[1].Index = 10;

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• Directory name for non-generic Proprietary stuff

  - by George Bailey

  Is there a common or standard directory name for the company-specific stuff that exists in a server? This would include any crons, scripts, webserver docroots, programs, non-database storage areas, service codebases, etc. We could of course put crons in /etc/cron.d, put docroots in /home/webservd, scripts in one of the bin directories, but that would be messy. If XYZ Technology Corp wanted to have all the non-generic stuff in one place, would they make a directory /xyz or /home/xyz or is there an alternative directory name that is not company-specific, but intended for company-specific stuff? What is most common?

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• Firefox: tabs containing a single image sometimes show generic icon instead of thumbnail

  - by ??O?????

  My version of Firefox is 3.5.9, but I've had this issue since single-image tabs started showing a thumbnail of the contained image. Typically, a tab containing a single image will use a thumbnail of the image as the icon before the tab title. Sometimes, though, this icon will be the generic “shaded sphere on blank page” (or perhaps whatever your theme defaults to). I'm guessing this happens whenever height or width is larger than 1024, but I seem to recall (perhaps erroneously) exceptions to this rule. Anyway, hopefully someone will know the definite answer to: Why does this happen? Examples Images showing thumbnails Wikipedia/Natalie Portman #1 (600×887) Wikipedia/Natalie Portman #2 (789×1024) Images not showing thumbnails Wikipedia/BMW series 3 cars (1276×338) Wikipedia/Greek temple (2414×1740)

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• Set generic iptables rules?

  - by tftd

  This may be a really dumb question but how can you open a port on multiple interfaces without defining the interfaces? For example how do I open port 22 on all interfaces? On my machine I have some interfaces that are dynamic and may or may not be available so I have to set "generic" rules. This code is not working for me but I can't figure out why: # My default policy is to drop the input. # The other policies are required like that. $IPTABLES -P INPUT DROP $IPTABLES -P OUTPUT ACCEPT $IPTABLES -P FORWARD ACCEPT $IPTABLES -t nat -P POSTROUTING ACCEPT $IPTABLES -t nat -P PREROUTING ACCEPT $IPTABLES -t mangle -P OUTPUT ACCEPT $IPTABLES -t mangle -P PREROUTING ACCEPT #Open port 22 on all interfaces ? $IPTABLES -A INPUT -p tcp --dport 22 -j ACCEPT So apparently there's something wrong with the last line... but I can't see it?

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• generic DAO in java

  - by akshay

  I am trying to develop generic DAO in java.I have tried the following.Is this a good way to implement generic dao?I dont want to use hibernate.I am trying to make it as generic as possible so that i dont have to repeate the same code again and again. public abstract class AbstractDAO<T> { protected ResultSet findbyId(String tablename, Integer id){ ResultSet rs= null; try { // the following lins in not working; pStmt = cn.prepareStatement("SELECT * FROM "+ tablename+ "WHERE id = ?"); pStmt.setInt(1, id); rs = pStmt.executeQuery(); } catch (SQLException ex) { System.out.println("ERROR in findbyid " +ex.getMessage() +ex.getCause()); ex.printStackTrace(); }finally{ return rs; } } } Now i have public class UserDAO extends AbstractDAO<User>{ public List<User> findbyid(int id){ Resultset rs =findbyid("USERS",id) //USERS is tablename in db List<Users> users = convertToList(rs); return users; } private List<User> convertToList(ResultSet rs) { List<User> userList= new ArrayList(); User user= new User();; try { while (rs.next()) { user.setId(rs.getInt("id")); user.setUsername(rs.getString("username")); user.setFname(rs.getString("fname")); user.setLname(rs.getString("lname")); user.setUsertype(rs.getInt("usertype")); user.setPasswd(rs.getString("passwd")); userList.add(user); } } catch (SQLException ex) { Logger.getLogger(UserDAO.class.getName()).log(Level.SEVERE, null, ex); } return userList; } }

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• Annotation to make available generic type

  - by mdma

  Given an generic interface like interface DomainObjectDAO<T> { T newInstance(); add(T t); remove(T t); T findById(int id); // etc... } I'd like to create a subinterface that specifies the type parameter: interface CustomerDAO extends DomainObjectDAO<Customer> { // customer-specific queries - incidental. } The implementation needs to know the actual template parameter type, but of course type erasure means isn't available at runtime. Is there some annotation that I could include to declare the interface type? Something like @GenericParameter(Customer.class) interface CustomerDAO extends DomainObjectDAO<Customer> { } The implementation could then fetch this annotation from the interface and use it as a substitute for runtime generic type access. Some background: This interface is implemented using JDK dynamic proxies as outlined here. The non-generic version of this interface has been working well, but it would be nicer to use generics and not have to create a subinterface for each domain object type. The actual type is needed at runtime to implement the newInstance method, amongst others.

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• Accessing Static Methods on a Generic class in c#

  - by mrlane

  Hello, I have the following situation in code, which I suspect may be a bit dodgey: I have a class: abstract class DataAccessBase<T> : IDataAccess where T : AnotherAbstractClass This class DataAccessBase also has a static factory method which creates instances of derived classes of itself using an enum value in a which statement to decide which derived type to create: static IDataAccess CreateInstance(TypeToCreateEnum) Now, the types derived from DataAccessBase<T> are themselves NOT generic, they specify a type for T: class PoLcZoneData : DataAccessBase<PoLcZone> // PoLcZone is derived from AnotherAbstractClass So far I am not sure if this is pushing the limits of good use of generics, but what I am really concerned about is how to access the static CreateInstance() method in the first place: The way I am doing this at the moment is to simply pass any type T where T : AnotherAbstractClass. In particular I am passing AnotherAbstractClass itself. This allows compilation just fine, but it does seem to me that passing any type to a generic class just to get at the statics is a bit dodgey. I have actually simplified the situation somewhat as DataAccessBase<T> is the lower level in the inheritance chain, but the static factory methods exists in a middle tier with classes such as PoLcZoneData being the most derived on the only level that is not generic. What are peoples thoughts on this arrangement?

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• Generic property- specify the type at runtime

  - by Lirik

  I was reading a question on making a generic property, but I'm a little confused at by the last example from the first answer (I've included the relevant code below): You have to know the type at compile time. If you don't know the type at compile time then you must be storing it in an object, in which case you can add the following property to the Foo class: public object ConvertedValue { get { return Convert.ChangeType(Value, Type); } } That's seems strange: it's converting the value to the specified type, but it's returning it as an object when the value was stored as an object. Doesn't the returned object still require un-boxing? If it does, then why bother with the conversion of the type? I'm also trying to make a generic property whose type will be determined at run time: public class Foo { object Value {get;set;} Type ValType{get;set;} Foo(object value, Type type) { Value = value; ValType = type; } // I need a property that is actually // returned as the specified value type... public object ConvertedValue { get { return Convert.ChangeType(Value, ValType); } } } Is it possible to make a generic property? Does the return property still require unboxing after it's accessed?

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• gdb: Cannot find new threads: generic error

  - by Alexander Gladysh

  When I run GDB against a program which loads a .so which is linked to pthreads, GDB reports error "Cannot find new threads: generic error". I probably miss something in my Ubuntu configuration (as it was installed from minimal install). Any clues? $ gdb --args lua -lluarocks.require GNU gdb (GDB) 7.0-ubuntu Copyright (C) 2009 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". For bug reporting instructions, please see: <http://www.gnu.org/software/gdb/bugs/>... Reading symbols from /usr/bin/lua...(no debugging symbols found)...done. (gdb) run Starting program: /usr/bin/lua -lluarocks.require Lua 5.1.4 Copyright (C) 1994-2008 Lua.org, PUC-Rio require 'ev' [Thread debugging using libthread_db enabled] Cannot find new threads: generic error (gdb) q A debugging session is active. Inferior 1 [process 4986] will be killed. Quit anyway? (y or n) y This function gets called on require 'ev': http://github.com/brimworks/lua-ev/blob/master/lua_ev.c#L25-65 Additional information about my system: $ uname -a Linux localhost 2.6.31-20-generic #58-Ubuntu SMP Fri Mar 12 04:38:19 UTC 2010 x86_64 GNU/Linux $ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 9.10 Release: 9.10 Codename: karmic

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• Checking instance of non-class constrained type parameter for null in generic method

  - by casperOne

  I currently have a generic method where I want to do some validation on the parameters before working on them. Specifically, if the instance of the type parameter T is a reference type, I want to check to see if it's null and throw an ArgumentNullException if it's null. Something along the lines of: // This can be a method on a generic class, it does not matter. public void DoSomething<T>(T instance) { if (instance == null) throw new ArgumentNullException("instance"); Note, I do not wish to constrain my type parameter using the class constraint. I thought I could use Marc Gravell's answer on "How do I compare a generic type to its default value?", and use the EqualityComparer<T> class like so: static void DoSomething<T>(T instance) { if (EqualityComparer<T>.Default.Equals(instance, null)) throw new ArgumentNullException("instance"); But it gives a very ambiguous error on the call to Equals: Member 'object.Equals(object, object)' cannot be accessed with an instance reference; qualify it with a type name instead How can I check an instance of T against null when T is not constrained on being a value or reference type?

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• Having Issue with Bounded Wildcards in Generic

  - by Sanjiv

  I am new to Java Generics, and I'm currently experimenting with Generic Coding....final goal is to convert old Non-Generic legacy code to generic one... I have defined two Classes with IS-A i.e. one is sub-class of other. public class Parent { private String name; public Parent(String name) { super(); this.name = name; } } public class Child extends Parent{ private String address; public Child(String name, String address) { super(name); this.address = address; } } Now, I am trying to create a list with bounded Wildcard. and getting Compiler Error. List<? extends Parent> myList = new ArrayList<Child>(); myList.add(new Parent("name")); // compiler-error myList.add(new Child("name", "address")); // compiler-error myList.add(new Child("name", "address")); // compiler-error Bit confused. please help me on whats wrong with this ?

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• Django: Serving a Download in a Generic View

  - by TheLizardKing

  So I want to serve a couple of mp3s from a folder in /home/username/music. I didn't think this would be such a big deal but I am a bit confused on how to do it using generic views and my own url. urls.py url(r'^song/(?P<song_id>\d+)/download/$', song_download, name='song_download'), The example I am following is found in the generic view section of the Django documentations: http://docs.djangoproject.com/en/dev/topics/generic-views/ (It's all the way at the bottom) I am not 100% sure on how to tailor this to my needs. Here is my views.py def song_download(request, song_id): song = Song.objects.get(id=song_id) response = object_detail( request, object_id = song_id, mimetype = "audio/mpeg", ) response['Content-Disposition'= "attachment; filename=%s - %s.mp3" % (song.artist, song.title) return response I am actually at a loss of how to convey that I want it to spit out my mp3 instead of what it does now which is to output a .mp3 with all of the current pages html contained. Should my template be my mp3? Do I need to setup apache to serve the files or is Django able to retrieve the mp3 from the filesystem(proper permissions of course) and serve that? If it do need to configure Apache how do I tell Django that? Thanks in advanced. These files are all on the HD so I don't need to "generate" anything on the spot and I'd like to prevent revealing the location of these files if at all possible. A simple /song/1234/download would be fantastic.

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• Linq-to-XML explicit casting in a generic method

  - by vlad

  I've looked for a similar question, but the only one that was close didn't help me in the end. I have an XML file that looks like this: <Fields> <Field name="abc" value="2011-01-01" /> <Field name="xyz" value="" /> <Field name="tuv" value="123.456" /> </Fields> I'm trying to use Linq-to-XML to get the values from these fields. The values can be of type Decimal, DateTime, String and Int32. I was able to get the fields one by one using a relatively simple query. For example, I'm getting the 'value' from the field with the name 'abc' using the following: private DateTime GetValueFromAttribute(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == "abc" select (DateTime)field.Attribute("value")).FirstOrDefault() } this is placed in a separate function that simply returns this value, and everything works fine (since I know that there is only one element with the name attribute set to 'abc'). however, since I have to do this for decimals and integers and dates, I was wondering if I can make a generic function that works in all cases. this is where I got stuck. here's what I have so far: private T GetValueFromAttribute<T>(IEnumerable<XElement> fields, String attName) { return (from field in fields where field.Attribute("name").Value == attName select (T)field.Attribute("value").Value).FirstOrDefault(); } this doesn't compile because it doesn't know how to convert from String to T. I tried boxing and unboxing (i.e. select (T) (Object) field.Attribute("value").Value but that throws a runtime Specified cast is not valid exception as it's trying to convert the String to a DateTime, for instance. Is this possible in a generic function? can I put a constraint on the generic function to make it work? or do I have to have separate functions to take advantage of Linq-to-XML's explicit cast operators?

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• Namespace scoped aliases for generic types in C#

  - by TN

  Let's have a following example: public class X { } public class Y { } public class Z { } public delegate IDictionary<Y, IList<Z>> Bar(IList<X> x, int i); public interface IFoo { // ... Bar Bar { get; } } public class Foo : IFoo { // ... public Bar Bar { get { return null; //... } } } void Main() { IFoo foo; //= ... IEnumerable<IList<X>> source; //= ... var results = source.Select(foo.Bar); } The compiler says: The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. It's because, it cannot convert Bar to Func<IList<X>, int, IDictionary<Y, IList<Z>>>. It would be great if I could create type namespace scoped type aliases for generic types in C#. Then I would define Bar not as a delegate, but rather I would define it as an namespace scoped alias for Func<IList<X>, int, IDictionary<Y, IList<Z>>>. public alias Bar = Func<IList<X>, int, IDictionary<Y, IList<Z>>>; I could then also define namespace scoped alias for e.g. IDictionary<Y, IList<Z>>. And if used appropriately:), it will make the code more readable. Now I have inline the generic types and the real code is not well readable:( Have you find the same trouble:)? Is there any good reason why it is not in C# 3.0? Or there is no good reason, it's just matter of money and/or time? EDIT: I know that I can use using, but it is not namespace based - not so convenient for my case.

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• Sort queryset by a generic foreign key (django)?

  - by thornomad

  I am using Django's comment framework which utilizes generic foreign keys. Question: How do I sort a given model's queryset by their comment count using the generic foreign key lookup? Reading the django docs on the subject it says one needs to calculate them not using the aggregation API: Django's database aggregation API doesn't work with a GenericRelation. [...] For now, if you need aggregates on generic relations, you'll need to calculate them without using the aggregation API. The only way I can think of, though, would be to iterate through my queryset, generate a list with content_type and object_id's for each item, then run a second queryset on the Comment model filtering by this list of content_type and object_id ... sort the objects by the count, then re-create a new queryset in this order by pulling the content_object for each comment ... This just seems wrong and I'm not even sure how to pull it off. Ideas? Someone must have done this before. I found this post online but it requires me handwriting SQL -- is that really necessary ?

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• Generic list/sublist handling

  - by user628661

  Let's say we have a class class ComplexCls { public int Fld1; public string Fld2; //could be more fields } class Cls { public int SomeField; } and then some code class ComplexClsList: List<ComplexCls>; ComplexClsList myComplexList; // fill myComplexList // same for Cls class ClsList : List<Cls>; ClsList myClsList; We want to populate myClsList from myComplexList, something like (pseudocode): foreach Complexitem in myComplexList { Cls ClsItem = new Cls(); ClsItem.SomeField = ComplexItem.Fld1; } The code to do this is easy and will be put in some method in myClsList. However I'd like to design this as generic as possible, for generic ComplexCls. Note that the exact ComplexCls is known at the moment of using this code, only the algorithm shd be generic. I know it can be done using (direct) reflection but is there other solution? Let me know if the question is not clear enough. (probably isn't). [EDIT] Basically, what I need is this: having myClsList, I need to specify a DataSource (ComplexClsList) and a field from that DataSource (Fld1) that will be used to populate my SomeField

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• Generic RPM package for Python 2.x

  - by RaphDG

  I have a python application, it can run on Python = 2.6 and it's architecture independant. I need the rpm package of this application to be installed on Fedora 14 (python 2.7) and Centos 6.2 (python 2.6). I currently use mock to build one rpm package for each "flavour" and it works well. I apparently can't install the Centos compiled rpm on Fedora. It gives me this error message : error: Failed dependencies: python(abi) = 2.6 is needed by myapp-0.9.el6.noarch Here is the relevant part of my .spec file : %{!?python_sitelib: %global python_sitelib %(%{__python} -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())")} %{!?python_sitearch: %global python_sitearch %(%{__python} -c "from distutils.sysconfig import get_python_lib; print(get_python_lib(1))")} Name: myapp Version: #VERSION# Release: #RELEASE#%{dist} Summary: myapp Group: Development/Languages License: Apache v2 Source0: %{name}-%{version}-#RELEASE#.tar.gz BuildRoot: %{_tmppath}/%{name}-%{version}-%{release}-root-%(%{__id_u} -n) BuildArch: noarch BuildRequires: python-devel BuildRequires: python-setuptools %description myapp %prep %setup -c %build %{__python} setup.py build %install %{__rm} -rf %{buildroot} %{__python} setup.py install -O1 --skip-build --root %{buildroot} Do I really have to use mock and build 2 rpms or is there another way to create a single generic 2.x rpm package ?

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• Java constructor using generic types

  - by user37903

  I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method initBreweryFromObject() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // initBreweryFromObject() is an instance method // of Brewery, of which <T> is a subclass (right?) c.initBreweryFromObject(); // "The method initBreweryFromObject() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void androidMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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• Is my "Generic" USB Flash Drive broken?

  - by Jesse J.

  So here is the situation. I find myself technological knowledgeable about many things ( I love to code, whether it's websites, C#, C++ or so on). However: My 2 toddlers (my wife actually) bought me a "Generic" 128 GB USB Storage Device (Usb Flash Drive) for Father's Day. I thought awesome at first..... WRONG! Nothing but problems with it. 3-4mb/s MAX transfer speed. I can bear with it. BUT! When I went to reformat my computer I transferred my save files from my games over to the stick and then the USB Stick managed to become corrupted. Not just a simple format would work either. It's screwed. I tried to use (Manually changed usb drive letter troubleshooting it to X) "chmod X: /X /F /R" with administrator rights, I did this after a long session to make it work with no errors (had to delete the log) and I finally recovered the files, however when I go to use it (transfer to or from) it transfers a couple kb to the stick or from it and then freezes, It says (Windows 7): Name: From: Folder (X:\File\Location) To: Folder C:\Users\Username\Desktop) Items Remaining: 0 (0 bytes) Speed: 0 bytes/second It does this forever... and ever... and ever... It transfered 3 files atleast, and then stopped. This is a new USB Stick bought from a "High" reputation company on eBay. Is the USB Stick screwed?

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• Un blogueur dévoile un iPhone tournant sous Android, alors que les relations entre Google et Apple s

  Un blogueur dévoile un iPhone tournant sous Android, alors que les relations entre Google et Apple sont au plus mal Alors que la situation est des plus tendues entre Apple et Google, les deux concurrents se retrouvent réunis sur un même appareil. Un informaticien passionné a en effet trouvé le moyen de faire tourner son iPhone sous Android. Cela fait déjà un an qu'il essaie et expérimentent divers techniques pour arriver à cette cohabitation de systèmes, avec plus ou moins de succès. Il dit avoir perdu du temps en se laissant distraire par le jailbreak. Grâce au dual boot, ils peuvent passer le l'OS iPhone à celui de Google. Planetbeing, le blogueur derrière cette initiative, a publié aujourd'hui une v...

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• Creating multiple relationships in rails with same datatypes

  - by Lowgain

  What I am trying to do is kind of like this: I have datatypes "user" and "article" for instance. I want to have relationships between these two, but in more than one way. So for instance, I'd like to let a user "like" or "bookmark" an article. So I need to have two relations in the database, one for users liking the article, and one for users bookmarking, so making a "user_article" table for instance won't be sufficient, correct? What is the best way of going about doing this?

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• Fastest way to convert datatable to generic list

  - by Joel Coehoorn

  I have a data tier select method that returns a datatable. It's called from a business tier method that should then return a strongly typed generic List. What I want to do is very similar (but not the same as) this question: http://stackoverflow.com/questions/208532/how-do-you-convert-a-datatable-into-a-generic-list What's different is that I want the list to contain strongly-typed objects rather than datarows (also, I don't have linq avaiable here yet). I'm concerned about performance. The business tier method will in turn be called from the presentation tier, and the results will be iterated for display to the user. It seems very wasteful to add an extra iteration at the business tier, only do it again right away for the presentation, so I want this to be as quick as possible. This is a common task, so I'm really looking for a good pattern that can be repeated over and over.

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• working with generic lifetime managers in unity config section

  - by Martin Bailey

  I have the following generic lifetime manager public class RequestLifetimeManager<T> : LifetimeManager, IDisposable { public override object GetValue() { return HttpContext.Current.Items[typeof(T).AssemblyQualifiedName]; } public override void RemoveValue() { HttpContext.Current.Items.Remove(typeof(T).AssemblyQualifiedName); } public override void SetValue(object newValue) { HttpContext.Current.Items[typeof(T).AssemblyQualifiedName] = newValue; } public void Dispose() { RemoveValue(); } } How do I reference this in the unity config section. Creating a type alias <typeAlias alias="requestLifeTimeManager`1" type=" UI.Common.Unity.RequestLifetimeManager`1, UI.Common" /> and specifying it as a lifetime manager <types> <type type="[interface]" mapTo="[concretetype]" > <lifetime type="requestLifeTimeManager`1" /> </type> </types> causes the following error Cannot create an instance of UI.Common.Unity.RequestLifetimeManager`1[T] because Type.ContainsGenericParameters is true. How do you reference generic lifetime managers ?

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