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• Implicit Type Conversions in Reflection

  - by bradhe

  So I've written a quick bit of code to help quickly convert between business objects and view models. Not to pimp my own blog, but you can find the details here if you're interested or need to know. One issue I've run in to is that I have a custom collection type, ProductCollection, and I need to turn that in to a string[] in on my model. Obviously, since there is no default implicit cast, I'm getting an exception in my contract converter. So, I thought I would write the next little bit of code and that should solve the problem: public static implicit operator string[](ProductCollection collection) { var list = new List<string>(); foreach (var product in collection) { if (product.Id == null) { list.Add(null); } else { list.Add(product.Id.ToString()); } } return list.ToArray(); } However, it still fails with the same cast exception. I'm wondering if it has something to do with being in reflection? If so, is there anything that I can do here?? I'm open to architectural solutions, too!

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• How do actually castings work at the CLR level?

  - by devoured elysium

  When doing an upcast or downcast, what does really happen behind the scenes? I had the idea that when doing something as: string myString = "abc"; object myObject = myString; string myStringBack = (string)myObject; the cast in the last line would have as only purpose tell the compiler we are safe we are not doing anything wrong. So, I had the idea that actually no casting code would be embedded in the code itself. It seems I was wrong: .maxstack 1 .locals init ( [0] string myString, [1] object myObject, [2] string myStringBack) L_0000: nop L_0001: ldstr "abc" L_0006: stloc.0 L_0007: ldloc.0 L_0008: stloc.1 L_0009: ldloc.1 L_000a: castclass string L_000f: stloc.2 L_0010: ret Why does the CLR need something like castclass string? There are two possible implementations for a downcast: You require a castclass something. When you get to the line of code that does an castclass, the CLR tries to make the cast. But then, what would happen had I ommited the castclass string line and tried to run the code? You don't require a castclass. As all reference types have a similar internal structure, if you try to use a string on an Form instance, it will throw an exception of wrong usage (because it detects a Form is not a string or any of its subtypes). Also, is the following statamente from C# 4.0 in a Nutshell correct? Upcasting and downcasting between compatible reference types performs reference conversions: a new reference is created that points to the same object. Does it really create a new reference? I thought it'd be the same reference, only stored in a different type of variable. Thanks

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• Java RMI Proxy issue

  - by Antony Lewis

  i am getting this error : java.lang.ClassCastException: $Proxy0 cannot be cast to rmi.engine.Call at Main.main(Main.java:39) my abstract and call class both extend remote. call: public class Call extends UnicastRemoteObject implements rmi.engine.Abstract { public Call() throws Exception { super(Store.PORT, new RClient(), new RServer()); } public String getHello() { System.out.println("CONN"); return "HEY"; } } abstract: public interface Abstract extends Remote { String getHello() throws RemoteException; } this is my main: public static void main(String[] args) { if (args.length == 0) { try { System.out.println("We are slave "); InetAddress ip = InetAddress.getLocalHost(); Registry rr = LocateRegistry.getRegistry(ip.getHostAddress(), Store.PORT, new RClient()); Object ss = rr.lookup("FILLER"); System.out.println(ss.getClass().getCanonicalName()); System.out.println(((Call)ss).getHello()); } catch (Exception e) { e.printStackTrace(); } } else { if (args[0].equals("master")) { // Start Master try { RMIServer.start(); } catch (Exception e) { e.printStackTrace(); } } Netbeans says the problem is on line 39 which is System.out.println(((Call)ss).getHello()); the output looks like this: run: We are slave Connecting 10.0.0.212:5225 $Proxy0 java.lang.ClassCastException: $Proxy0 cannot be cast to rmi.engine.Call at Main.main(Main.java:39) BUILD SUCCESSFUL (total time: 1 second) i am running a master in cmd listening on port 5225.

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• LLVM: Passing a pointer to a struct, which holds a pointer to a function, to a JIT function

  - by Rusky

  I have an LLVM (version 2.7) module with a function that takes a pointer to a struct. That struct contains a function pointer to a C++ function. The module function is going to be JIT-compiled, and I need to build that struct in C++ using the LLVM API. I can't seem get the pointer to the function as an LLVM value, let alone pass a pointer to the ConstantStruct that I can't build. I'm not sure if I'm even on the track, but this is what I have so far: void print(char*); vector<Constant*> functions; functions.push_back(ConstantExpr::getIntToPtr( ConstantInt::get(Type::getInt32Ty(context), (int)print), /* function pointer type here, FunctionType::get(...) doesn't seem to work */ )); ConstantStruct* struct = cast<ConstantStruct>(ConstantStruct::get( cast<StructType>(m->getTypeByName("printer")), functions )); Function* main = m->getFunction("main"); vector<GenericValue> args; args[0].PointerVal = /* not sure what goes here */ ee->runFunction(main, args);

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• OOP C# Question: Making a Fruit a Pear

  - by Adam Kane

  Given that I have an instance of Fruit with some properties set, and I want to get those properties into a new Pear instance (because this particular Fruit happens to have the qualities of a pear), what's the best way to achieve this effect? For example, what we can't do is simple cast a Fruit to a Pear, because not all Fruits are Pears: public static class PearGenerator { public static Pear CreatePear () { // Make a new generic fruit. Fruit genericFruit = new Fruit(); // Upcast it to a pear. (Throws exception: Can't cast a Fruit to a Pear.) Pear pear = (Pear)genericFruit; // Return freshly grown pear. return ( pear ); } } public class Fruit { // some code } public class Pear : Fruit { public void PutInPie () { // some code } } Thanks! Update: I don't control the "new Fruit()" code. My starting point is that I've got a Fruit to work with. I need to get that Fruit into a new Pear somehow. Maybe copy all the properties one by one?

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• Is there any performance issue using Row_Number to implement table paging in Sql Server 2008?

  - by majkinetor

  I want to implement table paging using this method: SET @PageNum = 2; SET @PageSize = 10; WITH OrdersRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY OrderDate, OrderID) AS RowNum ,* FROM dbo.Orders ) SELECT * FROM OrdersRN WHERE RowNum BETWEEN (@PageNum - 1) * @PageSize + 1 AND @PageNum * @PageSize ORDER BY OrderDate ,OrderID; Is there anything I should be aware of ? Table has millions of records. Thx. EDIT: After using suggested MAXROWS method for some time (which works really really fast) I had to switch back to ROW_NUMBER method because of its greater flexibility. I am also very happy about its speed so far (I am working with View having more then 1M records with 10 columns). To use any kind of query I use following modification: PROCEDURE [dbo].[PageSelect] ( @Sql nvarchar(512), @OrderBy nvarchar(128) = 'Id', @PageNum int = 1, @PageSize int = 0 ) AS BEGIN SET NOCOUNT ON Declare @tsql as nvarchar(1024) Declare @i int, @j int if (@PageSize <= 0) OR (@PageSize > 10000) SET @PageSize = 10000 -- never return more then 10K records SET @i = (@PageNum - 1) * @PageSize + 1 SET @j = @PageNum * @PageSize SET @tsql = 'WITH MyTableOrViewRN AS ( SELECT ROW_NUMBER() OVER(ORDER BY ' + @OrderBy + ') AS RowNum ,* FROM MyTableOrView WHERE ' + @Sql + ' ) SELECT * FROM MyTableOrViewRN WHERE RowNum BETWEEN ' + CAST(@i as varchar) + ' AND ' + cast(@j as varchar) exec(@tsql) END If you use this procedure make sure u prevented sql injection.

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• Omit return type in C++0x

  - by Clinton

  I've recently found myself using the following macro with gcc 4.5 in C++0x mode: #define RETURN(x) -> decltype(x) { return x; } And writing functions like this: template <class T> auto f(T&& x) RETURN (( g(h(std::forward<T>(x))) )) I've been doing this to avoid the inconvenience having to effectively write the function body twice, and having keep changes in the body and the return type in sync (which in my opinion is a disaster waiting to happen). The problem is that this technique only works on one line functions. So when I have something like this (convoluted example): template <class T> auto f(T&& x) -> ... { auto y1 = f(x); auto y2 = h(y1, g1(x)); auto y3 = h(y1, g2(x)); if (y1) { ++y3; } return h2(y2, y3); } Then I have to put something horrible in the return type. Furthermore, whenever I update the function, I'll need to change the return type, and if I don't change it correctly, I'll get a compile error if I'm lucky, or a runtime bug in the worse case. Having to copy and paste changes to two locations and keep them in sync I feel is not good practice. And I can't think of a situation where I'd want an implicit cast on return instead of an explicit cast. Surely there is a way to ask the compiler to deduce this information. What is the point of the compiler keeping it a secret? I thought C++0x was designed so such duplication would not be required.

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• Void* array casting to float, int32, int16, etc.

  - by Griffin

  Hey guys, I've got an array of PCM data, it could be 16 bit, 24 bit packed, 32 bit, etc.. It could be signed, or unsigned, and it could be 32 or 64 bit floating point. It is currently stored as a "void**" matrix, indexed by channel, then by frame. The goal is to allow my library to take in any PCM format and buffer it, without requiring manipulation of the data to fit a designated structure. If the A/D converter spits out 24 bit packed arrays of interleaved PCM, I need to accept it gracefully. I also need to support 16 bit non interleaved, as well as any permutation of the above formats. I know the bit depth and other information at runtime, and I'm trying to code efficiently while not duplicating code. What I need is an effective way to cast the matrix, put PCM data into the matrix, and then pull it out later. I can cast the matrix to int32_t, or int16_t for the 32 and 16 bit signed PCM respectively, I'll probably have to store the 24 bit PCM in an int32_t for 32 bit, 8 bit byte systems as well. Can anyone recommend a good way to put data into this array, and pull it out later? I'd like to avoid large sections of code which look like: switch( mFormat ) { case 1: // unsigned 8 bit for( int i = 0; i < mChannels; i++ ) framesArray = (uint8_t*)pcm[i]; break; case 2: // signed 8 bit for( int i = 0; i < mChannels; i++ ) framesArray = (int8_t*)pcm[i]; break; case 3: // unsigned 16 bit ... Limitations: I'm working in C/C++, no templates, no RTTI, no STL. Think embedded. Things get trickier when I have to port this to a DSP with 16 bit bytes. Does anybody have any useful macros they might be willing to share? Thanks, -Griff

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• Conditional row count in linq to nhibernate doesn't work

  - by Lucasus

  I want to translate following simple sql query into Linq to NHibernate: SELECT NewsId ,sum(n.UserHits) as 'HitsNumber' ,sum(CASE WHEN n.UserHits > 0 THEN 1 ELSE 0 END) as 'VisitorsNumber' FROM UserNews n GROUP BY n.NewsId My simplified UserNews class: public class AktualnosciUzytkownik { public virtual int UserNewsId { get; set; } public virtual int UserHits { get; set; } public virtual User User { get; set; } // UserId key in db table public virtual News News { get; set; } // NewsId key in db table } I've written following linq query: var hitsPerNews = (from n in Session.Query<UserNews>() group n by n.News.NewsId into g select new { NewsId = g.Key, HitsNumber = g.Sum(x => x.UserHits), VisitorsNumber = g.Count(x => x.UserHits > 0) }).ToList(); But generated sql just ignores my x => x.UserHits > 0 statement and makes unnecessary 'left outer join': SELECT news1_.NewsId AS col_0_0_, CAST(SUM(news0_.UserHits) AS INT) AS col_1_0_, CAST(COUNT(*) AS INT) AS col_2_0_ FROM UserNews news0_ LEFT OUTER JOIN News news1_ ON news0_.NewsId=news1_.NewsId GROUP BY news1_.NewsId How Can I fix or workaround this issue? Maybe this can be done better with QueryOver syntax?

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• byte + byte = int... why?

  - by Robert C. Cartaino

  Looking at this C# code... byte x = 1; byte y = 2; byte z = x + y; // ERROR: Cannot implicitly convert type 'int' to 'byte' The result of any math performed on byte (or short) types is implicitly cast back to an integer. The solution is to explicitly cast the result back to a byte, so... byte z = (byte)(x + y); // works What I am wondering is why? Is it architectural? Philosophical? We have: int + int = int long + long = long float + float = float double + double = double So why not: byte + byte = byte short + short = short ? A bit of background: I am performing a long list of calculations on "small numbers" (i.e. < 8) and storing the intermediate results in a large array. Using a byte array (instead of an int array) is faster (because of cache hits). But the extensive byte-casts spread through the code make it that much more unreadable.

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• Jersey, JAXB and getting an objectextending an abstract class as a parameter

  - by krajol

  I want to get an object as a parameter of a POST request. I got an abstract superclass that is called Promotion and subclasses Product and Percent. Here's how I try to get a request: @POST @Consumes(MediaType.APPLICATION_XML) @Produces(MediaType.APPLICATION_XML) @Path("promotion/") public Promotion createPromotion(Promotion promotion) { Product p = (Product) promotion; System.out.println(p.getPriceAfter()); return promotion; } and here's how I use JAXB in classes' definitions: @XmlRootElement(name="promotion") @XmlSeeAlso({Product.class,Percent.class}) public abstract class Promotion { //body } @XmlRootElement(name="promotion") public class Product extends Promotion { //body } @XmlRootElement(name="promotion") public class Percent extends Promotion { //body } So the problem now is when I send a POST request with a body like this: <promotion> <priceBefore>34.5</priceBefore> <marked>false</marked> <distance>44</distance> </promotion> and I try to cast it to Product (as in this case, fields 'marked' and 'distance' are from Promotion class and 'priceBefore' is from Product class) I get an Exception: java.lang.ClassCastException: Percent cannot be cast to Product. It seems like Percent is chosen as a 'default' subclass. Why is that and how can I get an object that is a Product?

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• How is timezone handled in the lifecycle of an ADO.NET + SQL Server DateTime column?

  - by stimpy77

  Using SQL Server 2008. This is a really junior question and I could really use some elaborate information, but the information on Google seems to dance around the topic quite a bit and it would be nice if there was some detailed elaboration on how this works... Let's say I have a datetime column and in ADO.NET I set it to DateTime.UtcNow. 1) Does SQL Server store DateTime.UtcNow accordingly, or does it offset it again based on the timezone of where the server is installed, and then return it offset-reversed when queried? I think I know that the answer is "of course it stores it without offsetting it again" but want to be certain. So then I query for it and cast it from, say, an IDataReader column to a DateTime. As far as I know, System.DateTime has metadata that internally tracks whether it is a UTC DateTime or it is an offsetted DateTime, which may or may not cause .ToLocalTime() and .ToUniversalTime() to have different behavior depending on this state. So, 2) Does this casted System.DateTime object already know that it is a UTC DateTime instance, or does it assume that it has been offset? Now let's say I don't use UtcNow, I use DateTime.Now, when performing an ADO.NET INSERT or UPDATE. 3) Does ADO.NET pass the offset to SQL Server and does SQL Server store DateTime.Now with the offset metadata? So then I query for it and cast it from, say, an IDataReader column to a DateTime. 4) Does this casted System.DateTime object already know that it is an offset time, or does it assume that it is UTC?

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• Casting pointer to object to void * in C++

  - by JB

  I've been reading StackOverflow too much and started doubting all the code I've ever written, I keep thinking "Is that undefined behavour?" even in code that has been working for ages. So my question - Is it safe and well defined behavour to cast a pointer to an object (In this case abstract interface classes) to a void* and then later on cast them back to the original class and call method using them? I'm fully aware that the code that does this is probably awful. I wouldn't even consider writing it like this now (this is old code which I don't really want to change), so I'm not looking for a discussion of better ways to do this. I already know how to write it better if I ever did this again. But if it's actually broken to rely on this in C++ then I'll have to look at changing the code, if it's merely awful code then changing it won't be a priority. I would have had no doubts about something this simple a year or two ago but as my understanding of C++ increases I actually find I have more and more worries about code being safe under the standards even if it works perfectly well. Perhaps reading too much stack overflow is a bad thing for productivity sometimes :P

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• IList<T> vs IEnumerable<T>. What is more efficient IList<T> or IEnumerable<T>

  - by bigb

  What is more efficient way to make methods return IList<T> or IEnumerable<T>? IEnumerable<T> it is immutable collection but IList<T> mutable and contain a lot of useful methods and properties. To cast IList<T> to IEnumerable<T> it is just reference copy: IList<T> l = new List<T>(); IEnumerable<T> e = l; To cast IEnumerable<T> to List<T> we need to iterate each element or to call ToList() method: IEnumerable<T>.ToList(); or may pass IEnumerable<T> to List<T> constructor which doing the same iteration somewhere within its constructor. List<T> l = new List<T>(e); Which cases you think is more efficient? Which you prefer more in your practice?

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• Access array of c-structs using Python ctypes

  - by sadris

  I have a C-function that allocates memory at the address passed to and is accessed via Python. The pointer contents does contain an array of structs in the C code, but I am unable to get ctypes to access the array properly beyond the 0th element. How can I get the proper memory offset to be able to access the non-zero elements? Python's ctypes.memset is complaining about TypeErrors if I try to use their ctypes.memset function. typedef struct td_Group { unsigned int group_id; char groupname[256]; char date_created[32]; char date_modified[32]; unsigned int user_modified; unsigned int user_created; } Group; int getGroups(LIBmanager * handler, Group ** unallocatedPointer); ############# python code below: class Group(Structure): _fields_ = [("group_id", c_uint), ("groupname", c_char*256), ("date_created", c_char*32), ("date_modified", c_char*32), ("user_modified", c_uint), ("user_created", c_uint)] myGroups = c_void_p() count = libnativetest.getGroups( nativePointer, byref(myGroups) ) casted = cast( myGroups, POINTER(Group*count) ) for x in range(0,count): theGroup = cast( casted[x], POINTER(Group) ) # this only works for the first entry in the array: print "~~~~~~~~~~" + theGroup.contents.groupname Related: Access c_char_p_Array_256 in Python using ctypes

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• Why Is the sender type null when dealing with events

  - by ChloeRadshaw

  From C# Via CLR: Note A lot of people wonder why the event pattern requires the sender parameter to always be of type Object After all, since the MailManager will be the only type raising an event with a NewMail EventArgs object, it makes more sense for the callback method to be prototyped like this: void MethodName(Mai l Manager sender, NewMail EventArgs e); The pattern requires the sender parameter to be of type Object mostly because of inheritance What if Mai lManager were used as a base class for SmtpMailManager? In this case, the callback method should have the sender parameter prototyped as SmtpMailManager instead of Mail Manager, but this can’t happen because SmtpMai lManager just inherited the NewMai l event So the code that was expecting SmtpMail Manager to raise the event must still have to cast the sender argument to SmtpMailManager In other words, the cast is still required, so the sender parameter might as well be typed as Obj ect The next reason for typing the sender parameter as Obj ect is just fexibility It allows the delegate to be used by multiple types that offer an event that passes a NewMail EventArgs object For example, a PopMai lManager class could use the delegate even if this class were not derived from Mail Manager I just simply cannot understand why the sender is an object - Why can it not be generified? so most of the time we do not need to do generic casts

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• C# casting question: from IEnumerable to custom type

  - by Sarah Vessels

  I have a custom class called Rows that implements IEnumerable<Row>. I often use LINQ queries on Rows instances: Rows rows = new Rows { row1, row2, row3 }; IEnumerable<Row> particularRows = rows.Where<Row>(row => condition); What I would like is to be able to do the following: Rows rows = new Rows { row1, row2, row3 }; Rows particularRows = (Rows)rows.Where<Row>(row => condition); However, I get a "System.InvalidCastException: Unable to cast object of type 'WhereEnumerableIterator1[NS.Row]' to type 'NS.Rows'". I do have a Rows constructor taking IEnumerable<Row>, so I could do: Rows rows = new Rows { row1, row2, row3 }; Rows particularRows = new Rows(rows.Where<Row>(row => condition)); This seems bulky, however, and I would love to be able to cast an IEnumerable<Row> to be a Rows since Rows implements IEnumerable<Row>. Any ideas?

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• C++ ulong to class method pointer and back

  - by Simone Margaritelli

  Hi guys, I'm using a hash table (source code by Google Inc) to store some method pointers defined as: typedef Object *(Executor::*expression_delegate_t)( vframe_t *, Node * ); Where obviously "Executor" is the class. The function prototype to insert some value to the hash table is: hash_item_t *ht_insert( hash_table_t *ht, ulong key, ulong data ); So basically i'm doing the insert double casting the method pointer: ht_insert( table, ASSIGN, reinterpret_cast<ulong>( (void *)&Executor::onAssign ) ); Where table is defined as a 'hash_table_t *' inside the declaration of the Executor class, ASSIGN is an unsigned long value, and 'onAssign' is the method I have to map. Now, Executor::onAssign is stored as an unsigned long value, its address in memory I think, and I need to cast back the ulong to a method pointer. But this code: hash_item_t* item = ht_find( table, ASSIGN ); expression_delegate_t delegate = reinterpret_cast < expression_delegate_t > (item->data); Gives me the following compilation error : src/executor.cpp:45: error: invalid cast from type ‘ulong’ to type ‘Object* (Executor::*)(vframe_t*, Node*)’ I'm using GCC v4.4.3 on a x86 GNU/Linux machine. Any hints?

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• Would you allow this type of query?

  - by user564577

  I'm exploring using an ORM tool in our development shop, and in particular Entity Framework 4.0. Since we work with VERY large databases, I'm a bit concerned about the query's it generates. Doing something simple like getting clients with an address in a state looks like below. As a database developer or admin would you allow this? Is it as bad as it looks? Assume every join is on a clustered index. SELECT [Project2].[ClientKey] AS [ClientKey], [Project2].[FirstName] AS [FirstName], [Project2].[LastName] AS [LastName], [Project2].[IsEnabled] AS [IsEnabled], [Project2].[ChangeUser] AS [ChangeUser], [Project2].[ChangeDate] AS [ChangeDate], [Project2].[C1] AS [C1], [Project2].[AddressKey] AS [AddressKey], [Project2].[ClientKey1] AS [ClientKey1], [Project2].[AddressTypeCode] AS [AddressTypeCode], [Project2].[PrimaryAddress] AS [PrimaryAddress], [Project2].[AddressLine1] AS [AddressLine1], [Project2].[AddressLine2] AS [AddressLine2], [Project2].[City] AS [City], [Project2].[State] AS [State], [Project2].[ZIP] AS [ZIP] FROM ( SELECT [Distinct1].[ClientKey] AS [ClientKey], [Distinct1].[FirstName] AS [FirstName], [Distinct1].[LastName] AS [LastName], [Distinct1].[IsEnabled] AS [IsEnabled], [Distinct1].[ChangeUser] AS [ChangeUser], [Distinct1].[ChangeDate] AS [ChangeDate], [Extent3].[AddressKey] AS [AddressKey], [Extent3].[ClientKey] AS [ClientKey1], [Extent3].[AddressTypeCode] AS [AddressTypeCode], [Extent3].[PrimaryAddress] AS [PrimaryAddress], [Extent3].[AddressLine1] AS [AddressLine1], [Extent3].[AddressLine2] AS [AddressLine2], [Extent3].[City] AS [City], [Extent3].[State] AS [State], [Extent3].[ZIP] AS [ZIP], CASE WHEN ([Extent3].[AddressKey] IS NULL) THEN CAST(NULL AS int) ELSE 1 END AS [C1] FROM (SELECT DISTINCT [Extent1].[ClientKey] AS [ClientKey], [Extent1].[FirstName] AS [FirstName], [Extent1].[LastName] AS [LastName], [Extent1].[IsEnabled] AS [IsEnabled], [Extent1].[ChangeUser] AS [ChangeUser], [Extent1].[ChangeDate] AS [ChangeDate] FROM [Common].[Clients] AS [Extent1] INNER JOIN [Common].[ClientAddresses] AS [Extent2] ON [Extent1].[ClientKey] = [Extent2].[ClientKey] WHERE (( CAST(CHARINDEX(UPPER('D'), UPPER([Extent1].[LastName])) AS int)) > 0) AND ([Extent1].[IsEnabled] = 1) AND ([Extent2].[City] IS NOT NULL) AND ((UPPER([Extent2].[City])) = (UPPER('Colorado Springs'))) ) AS [Distinct1] LEFT OUTER JOIN [Common].[ClientAddresses] AS [Extent3] ON [Distinct1].[ClientKey] = [Extent3].[ClientKey] ) AS [Project2] ORDER BY [Project2].[ClientKey] ASC, [Project2].[FirstName] ASC, [Project2].[LastName] ASC, [Project2].[IsEnabled] ASC, [Project2].[ChangeUser] ASC, [Project2].[ChangeDate] ASC, [Project2].[C1] ASC

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• How to get from JRuby a correctly typed ruby implementation of a Java interface?

  - by Guss

  I'm trying to use JRuby (through the JSR233 interface included in JRuby 1.5) from a Java application to load a ruby implementation of a Java interface. My sample implementation looks like this: Interface: package some.package; import java.util.List; public interface ScriptDemoIf { int fibonacci(int d); List<String> filterLength(List<String> source, int maxlen); } Ruby Implementation: require 'java' include Java class ScriptDemo java_implements some.package.ScriptDemoIf java_signature 'int fibonacci(int d)' def fibonacci(d) d < 2 ? d : fibonacci(d-1) + fibonacci(d-2) end java_signature 'List<String> filterLength(List<String> source, int maxlen)' def filterLength(source, maxlen) source.find_all { |str| str.length <= maxlen } end end Class loader: public ScriptDemoIf load(String filename) throws ScriptException { ScriptEngine engine = new ScriptEngineManager().getEngineByName("jruby"); FileReader script = new FileReader(filename); try { engine.eval(new FileReader(script)); } catch (FileNotFoundException e) { throw new ScriptException("Failed to load " + filename); } return (ScriptDemoIf) m_engine.eval("ScriptDemo.new"); } (Obviously the loader is a bit more generic in real life - it doesn't assume that the implementation class name is "ScriptDemo" - this is just for simplicity). Problem - I get a class cast exception in the last line of the loader - the engine.eval() return a RubyObject type which doesn't cast down nicely to my interface. From stuff I read all over the web I was under the impression that the whole point of use java_implements in the Ruby section was for the interface implementations to be compiled in properly. What am I doing wrong?

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• Can someone answer this for me?

  - by Dcurvez

  okay I am totally stuck. I have been getting some help off and on throughout this project and am anxious to get this problem solved so I can continue on with the rest of this project. I have a gridview that is set to save to a file, and has the option to import into excel. I keep getting an error of this: Invalid cast exception was unhandled. At least one element in the source array could not be cast down to the destination array type. Can anyone tell me in layman easy to understand what this error is speaking of? This is the code I am trying to use: Dim fileName As String = "" Dim dlgSave As New SaveFileDialog dlgSave.Filter = "Text files (*.txt)|*.txt|CSV Files (*.csv)|*.csv" dlgSave.AddExtension = True dlgSave.DefaultExt = "txt" If dlgSave.ShowDialog = Windows.Forms.DialogResult.OK Then fileName = dlgSave.FileName SaveToFile(fileName) End If End Sub Private Sub SaveToFile(ByVal fileName As String) If DataGridView1.RowCount > 0 AndAlso DataGridView1.Rows(0).Cells(0) IsNot Nothing Then Dim stream As New System.IO.FileStream(fileName, IO.FileMode.Append, IO.FileAccess.Write) Dim sw As New System.IO.StreamWriter(stream) For Each row As DataGridViewRow In DataGridView1.Rows Dim arrLine(9) As String Dim line As String **row.Cells.CopyTo(arrLine, 0)** line = arrLine(0) line &= ";" & arrLine(1) line &= ";" & arrLine(2) line &= ";" & arrLine(3) line &= ";" & arrLine(4) line &= ";" & arrLine(5) line &= ";" & arrLine(6) line &= ";" & arrLine(7) line &= ";" & arrLine(8) sw.WriteLine(line) Next sw.Flush() sw.Close() End If I bolded the line where it shows in debug, and I really dont see what all the fuss is about LOL

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• IDENTITY_INSERT ON inside of cursor does not allow inserted id

  - by Mac

  I am trying to set some id's for a bunch of rows in a database where the id column is an identity. I've created a cursor to loop through the rows and update the ids with incrementing negative numbers (-1,-2,-3 etc). When I updated just one row turning on the IDENTITY_INSERT it worked fine but as soon as I try and use it in a cursor, it throws the following error. Msg 8102, Level 16, State 1, Line 22 Cannot update identity column 'myRowID'. DECLARE @MinId INT; SET @MinId = (SELECT MIN(myRowId) FROM myTable)-1; DECLARE myCursor CURSOR FOR SELECT myRowId FROM dbo.myTable WHERE myRowId > 17095 OPEN myCursor DECLARE @myRowId INT FETCH NEXT FROM myCursor INTO @myRowId WHILE (@@FETCH_STATUS <> -1) BEGIN SET IDENTITY_INSERT dbo.myTable ON; --UPDATE dbo.myTable --SET myRowId = @MinId --WHERE myRowId = @myRowId; PRINT (N'ID: ' + CAST(@myRowId AS VARCHAR(10)) + N' NewID: ' + CAST(@MinId AS VARCHAR(4))); SET @MinId = @MinId - 1; FETCH NEXT FROM myCursor INTO @myRowId END CLOSE myCursor DEALLOCATE myCursor GO SET IDENTITY_INSERT dbo.myTable OFF; GO Does anyone know what I'm doing wrong?

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• Refactoring two methods down to one

  - by bflemi3

  I have two methods that almost do the same thing. They get a List<XmlNode> based on state OR state and schoolType and then return a distinct, ordered IEnumerable<KeyValuePair<string,string>>. I know they can be refactored but I'm struggling to determine what type the parameter should be for the linq statement in the return of the method (the last line of each method). I thank you for your help in advance. private IEnumerable<KeyValuePair<string, string>> getAreaDropDownDataSource() { StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument(); string schoolTypeXmlPath = string.Format(STATE_AND_SCHOOL_TYPE_XML_PATH, StateOfInterest, ConnectionsLearningSchoolType); var schoolNodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>()); return schoolNodes.Select(x => new KeyValuePair<string, string>(x.Attributes["idLocation"].Value, x.Value)).OrderBy(x => x.Key).Distinct(); } private IEnumerable<KeyValuePair<string, string>> getStateOfInterestDropDownDataSource() { StateInfoXmlDocument stateInfoXmlDocument = new StateInfoXmlDocument(); string schoolTypeXmlPath = string.Format(SCHOOL_TYPE_XML_PATH, ConnectionsLearningSchoolType); var schoolNodes = new List<XmlNode>(stateInfoXmlDocument.SelectNodes(schoolTypeXmlPath).Cast<XmlNode>()); return schoolNodes.Select(x => new KeyValuePair<string, string>(x.Attributes["stateCode"].Value, x.Attributes["stateName"].Value)).OrderBy(x => x.Key).Distinct(); }

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• Suggestions on Working with this Inherited Generic Method

  - by blu

  We have inherited a project that is a wrapper around a section of the core business model. There is one method that takes a generic, finds items matching that type from a member and then returns a list of that type. public List<T> GetFoos<T>() { List<IFoo> matches = Foos.FindAll( f => f.GetType() == typeof(T) ); List<T> resultList = new List<T>(); foreach (var match in matches) { resultList.Add((T)obj); } } Foos can hold the same object cast into various classes in inheritance hierarchy to aggregate totals differently for different UI presentations. There are 20+ different types of descendants that can be returned by GetFoos. The existing code basically has a big switch statement copied and pasted throughout the code. The code in each section calls GetFoos with its corresponding type. We are currently refactoring that into one consolidated area, but as we are doing that we are looking at other ways to work with this method. One thought was to use reflection to pass in the type, and that worked great until we realized the Invoke returned an object, and that it needed to be cast somehow to the List <T>. Another was to just use the switch statement until 4.0 and then use the dynamic language options. We welcome any alternate thoughts on how we can work with this method. I have left the code pretty brief, but if you'd like to know any additional details please just ask.

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• Best way to store data in database when you don't know the type

  - by stiank81

  I have a table in my database that represents datafields in a custom form. The DataField gives some representation of what kind of control it should be represented with, and what value type it should take. Simplified you can say that I have 2 entities in this table - Textbox taking any string and Textbox only taking numbers. Now I have the different values stored in a separate table, referencing the datafield definition. What is the best way to store the data value here, when the type differs? One possible solution is to have the FieldValue table hold one field per possible value type. Now this would certainly be redundant, but at least I would get the value stored in its correct form - simplifying queries later. FieldValue ---------- Id DataFieldId IntValue DoubleValue BoolValue DataValue .. Another possibility is just storing everything as String, and casting this in the queries. I am using .Net with NHibernate, and I see that at least here there is a Projections.Cast that can be used to cast e.g. string to int in the query. Either way in these two solutions I need to know which type to use when doing the query, but I will know that from the DataField, so that won't be a problem. Anyway; I don't think any of these solutions sounds good. Are they? Or is there a better way?

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