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• Simplifying Testing through design considerations while utilizing dependency injection

  - by Adam Driscoll

  We are a few months into a green-field project to rework the Logic and Business layers of our product. By utilizing MEF (dependency injection) we have achieved high levels of code coverage and I believe that we have a pretty solid product. As we have been working through some of the more complex logic I have found it increasingly difficult to unit test. We are utilizing the CompositionContainer to query for types required by these complex algorithms. My unit tests are sometimes difficult to follow due to the lengthy mock object setup process that must take place, just right, to allow for certain circumstances to be verified. My unit tests often take me longer to write than the code that I'm trying to test. I realize this is not only an issue with dependency injection but with design as a whole. Is poor method design or lack of composition to blame for my overly complex tests? I've tried base classing tests, creating commonly used mock objects and ensuring that I utilize the container as much as possible to ease this issue but my tests always end up quite complex and hard to debug. What are some tips that you've seen to keep such tests concise, readable, and effective?

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• .net runtime type casting when using reflection

  - by Mike

  I have need to cast a generic list of a concrete type to a generic list of an interface that the concrete types implement. This interface list is a property on an object and I am assigning the value using reflection. I only know the value at runtime. Below is a simple code example of what I am trying to accomplish: public void EmployeeTest() { IList<Employee> initialStaff = new List<Employee> { new Employee("John Smith"), new Employee("Jane Doe") }; Company testCompany = new Company("Acme Inc"); //testCompany.Staff = initialStaff; PropertyInfo staffProperty = testCompany.GetType().GetProperty("Staff"); staffProperty.SetValue(testCompany, (staffProperty.PropertyType)initialStaff, null); } Classes are defined like so: public class Company { private string _name; public string Name { get { return _name; } set { _name = value; } } private IList<IEmployee> _staff; public IList<IEmployee> Staff { get { return _staff; } set { _staff = value; } } public Company(string name) { _name = name; } } public class Employee : IEmployee { private string _name; public string Name { get { return _name; } set { _name = value; } } public Employee(string name) { _name = name; } } public interface IEmployee { string Name { get; set; } } Any thoughts? I am using .NET 4.0. Would the new covariant or contravariant features help? Thanks in advance.

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• Returning large collections from WCF Serivce

  - by Nate Bross

  I'm trying to determine the best approach for building a WCF Service, and the area I'm struggling with most is returning lists of objects. The built-in maxMessageSize of 64k seems pretty high, and I really don't want to bump it up (quick googling finds 100s of places bumping the maxMessageSize up to multi-gigabyte range which seems foolish). But, when I'm returning a collection of objects (~150 items) I am exceeding the default 64k. I'm almost to the point of returning my own class which inherits IEnumerable and has properties for hasNext, hasPrevious and PageSize so that I can implement paging on the client side -- this seems like alot of code. The other option is to jackup the maxMessageSize and hope for the best, but that feels wrong. All other aspects of my service are working great, its just returning large collectiosn where I'm having issues. For background, there are two types of consumers of this service, UI applications which will be primarly web and/or wpf applications, and data processing applications, .NET console apps, and maybe some other non-UI apps. For the UI applications, I would like to keep them responsive and keep the messageSize low, on the console apps it doesn't matter as much as they are just pulling data down to do processing and push it back up to the service.

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• Cant' cast a class with multiple inheritance

  - by Jay S.

  I am trying to refactor some code while leaving existing functionality in tact. I'm having trouble casting a pointer to an object into a base interface and then getting the derived class out later. The program uses a factory object to create instances of these objects in certain cases. Here are some examples of the classes I'm working with. // This is the one I'm working with now that is causing all the trouble. // Some, but not all methods in NewAbstract and OldAbstract overlap, so I // used virtual inheritance. class MyObject : virtual public NewAbstract, virtual public OldAbstract { ... } // This is what it looked like before class MyObject : public OldAbstract { ... } // This is an example of most other classes that use the base interface class NormalObject : public ISerializable // The two abstract classes. They inherit from the same object. class NewAbstract : public ISerializable { ... } class OldAbstract : public ISerializable { ... } // A factory object used to create instances of ISerializable objects. template<class T> class Factory { public: ... virtual ISerializable* createObject() const { return static_cast<ISerializable*>(new T()); // current factory code } ... } This question has good information on what the different types of casting do, but it's not helping me figure out this situation. Using static_cast and regular casting give me error C2594: 'static_cast': ambiguous conversions from 'MyObject *' to 'ISerializable *'. Using dynamic_cast causes createObject() to return NULL. The NormalObject style classes and the old version of MyObject work with the existing static_cast in the factory. Is there a way to make this cast work? It seems like it should be possible.

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• How do I create a selection list in ASP.NET MVC?

  - by Gary McGill

  I have a database table that records what publications a user is allowed to access. The table is very simple - it simply stores user ID/publication ID pairs: CREATE TABLE UserPublication (UserId INTEGER, PublicationID INTEGER) The presence of a record for a given user & publication means that the user has access; absence of a record implies no access. I want to present my admin users with a simple screen that allows them to configure which publications a user can access. I would like to show one checkbox for each of the possible publications, and check the ones that the user can currently access. The admin user can then check or un-check any number of publications and submit the form. There are various publication types, and I want to group the similarly-typed publications together - so I do need control over how the publications are presented (I don't want to just have a flat list). My view model obviously needs to have a list of all the publications (since I need to display them all regardless of the current selection), and I also need a list of the publications that the user currently has access to. (I'm not sure whether I'd be better off with a single list where each item includes the publication ID and a yes/no field?). But that's as far as I've got. I've really no idea how to go about binding this to some checkboxes. Where do I start?

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• Delphi RTTI unable to find interface

  - by conciliator

  I'm trying to fetch an interface using D2010 RTTI. program rtti_sb_1; {$APPTYPE CONSOLE} {$M+} uses SysUtils, Rtti, mynamespace in 'mynamespace.pas'; var ctx: TRttiContext; RType: TRttiType; MyClass: TMyIntfClass; begin ctx := TRttiContext.Create; MyClass := TMyIntfClass.Create; // This prints a list of all known types, including some interfaces. // Unfortunately, IMyPrettyLittleInterface doesn't seem to be one of them. for RType in ctx.GetTypes do WriteLn(RType.Name); // Finding the class implementing the interface is easy. RType := ctx.FindType('mynamespace.TMyIntfClass'); // Finding the interface itself is not. RType := ctx.FindType('mynamespace.IMyPrettyLittleInterface'); MyClass.Free; ReadLn; end. Both IMyPrettyLittleInterface and TMyIntfClass = class(TInterfacedObject, IMyPrettyLittleInterface) are declared in mynamespace.pas. Do anyone know why this doesn't work? Is there a way to solve my problem? Thanks in advance!

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• Many to many table design question

  - by user169867

  Originally I had 2 tables in my DB, [Property] and [Employee]. Each employee can have 1 "Home Property" so the employee table has a HomePropertyID FK field to Property. Later I needed to model the situation where despite having only 1 "Home Property" the employee did work at or cover for multiple properties. So I created an [Employee2Property] table that has EmployeeID and PropertyID FK fields to model this many 2 many relationship. Now I find that I need to create other many-to-many relationships between employees and properties. For example if there are multiple employees that are managers for a property or multiple employees that perform maintenance work at a property, etc. My questions are: 1) Should I create seperate many-to-many tables for each of these situations or should I just create 1 more table like [PropertyAssociatonType] that lists the types of associations an emploee can have with a property and just add a FK field to [Employee2Property] such a PropertyAssociationTypeID that explains what the association is? I'm curious about the pros/cons or if there's another better way. 2) Am I stupid and going about this all worng? Thanks for any suggestions :)

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• What's a good Java-based Master-Slave communication mechanism?

  - by plecong

  I'm creating a Java application that requires master-slave communication between JVMs, possibly residing on the same physical machine. There will be a "master" server running inside a JEE application server (i.e. JBoss) that will have "slave" clients connect to it and dynamically register itself for communication (that is the master will not know the IP addresses/ports of the slaves so cannot be configured in advance). The master server acts as a controller that will dole work out to the slaves and the slaves will periodically respond with notifications, so there would be bi-directional communication. I was originally thinking of RPC-based systems where each side would be a server, but it could get complicated, so I'd prefer a mechanism where there's an open socket and they talk back and forth. I'm looking for a communication mechanism that would be low-latency where the messages would be mostly primitive types, so no serious serialization is necessary. Here's what I've looked at: RMI JMS: Built-in to Java, the "slave" clients would connect to the existing ConnectionFactory in the application server. JAX-WS/RS: Both master and slave would be servers exposing an RPC interface for bi-directional communication. JGroups/Hazelcast: Use shared distributed data structures to facilitate communication. Memcached/MongoDB: Use these as "queues" to facilitate communication, though the clients would have to poll so there would be some latency. Thrift: This does seem to keep a persistent connection, but not sure how to integrate/embed a Thrift server into JBoss WebSocket/Raw Socket: This would work, but require a lot more custom code than I'd like. Is there any technology I'm missing? Edit: Also looked at: JMX: Have the client connect to JBoss' JMX server and receive JMX notifications for bidirectional comms.

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• Unboxing to unknown type

  - by Robert

  I'm trying to figure out syntax that supports unboxing an integral type (short/int/long) to its intrinsic type, when the type itself is unknown. Here is a completely contrived example that demonstrates the concept: // Just a simple container that returns values as objects struct DataStruct { public short ShortVale; public int IntValue; public long LongValue; public object GetBoxedShortValue() { return LongValue; } public object GetBoxedIntValue() { return LongValue; } public object GetBoxedLongValue() { return LongValue; } } static void Main( string[] args ) { DataStruct data; // Initialize data - any value will do data.LongValue = data.IntValue = data.ShortVale = 42; DataStruct newData; // This works if you know the type you are expecting! newData.ShortVale = (short)data.GetBoxedShortValue(); newData.IntValue = (int)data.GetBoxedIntValue(); newData.LongValue = (long)data.GetBoxedLongValue(); // But what about when you don't know? newData.ShortVale = data.GetBoxedShortValue(); // error newData.IntValue = data.GetBoxedIntValue(); // error newData.LongValue = data.GetBoxedLongValue(); // error } In each case, the integral types are consistent, so there should be some form of syntax that says "the object contains a simple type of X, return that as X (even though I don't know what X is)". Because the objects ultimately come from the same source, there really can't be a mismatch (short != long). I apologize for the contrived example, it seemed like the best way to demonstrate the syntax. Thanks.

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• Problem in filtering records using Dataview (C#3.0)

  - by Newbie

  I have a data table . The data table is basically getting populated from excel sheet. And there are many excel sheets. Henceforth, I have written a utility method for accomplishing the same. Now in some of the excel sheets, there are date columns and in some it is not(only text/string). My function is populating the values properly into the datatable from the excell sheet. But there are many blank rows in the excel sheets some are filled with NULL , some with " ". So I need to filter those records (which are NULL or " " ) first before further processing. What I am after is to use a dataview and apply the filter over there. DataView dv = dataTable.DefaultView; dv.RowFilter = ColumnName + " <> ''"; Well by using metedata (GetOleDbSchemaTable(OleDbSchemaGuid.Columns, restrection)) I was able to get the column names from the excel sheet , so getting the column names is not an issue. But the problem is as I said in some Excel sheet there are date fileds some are not. So the Filter condition of the Dataview needs to be proper. If I apply the above logic, and if it encounters a Datafield, it is throwing error Cannot perform '<' operation on System.DateTime and System.String. Could you people please help me out? I need to filter columns(not known at compile time + their data types) which can have NULL and " " I am using C#3.0 Thanks

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• How to choose light version of database system

  - by adopilot

  I am starting one POS (Point of sale) project. Targeting system is going to be written in C# .NET 2 WinForms and as main database server We are going to use MS-SQL Server. As we have a lot of POS devices in chain for one store I will love to have backend local data base system on each POS device. Scenario are following: When main server goes down!! POS application should continue working "off-line" with local database, until connection to main server come up again. Now I am in dilemma which local database is going to be most adoptable for me. Here is some notes for helping me point me in right direction: To be Light "My POS devices art usually old and suffering with performances" To be Free "I have a lot of devices and I do not wont additional cost beside main SQL serer" One day Ill love to try all that port on Mono and Linux OS. Here is what I've researched so far: Simple XML "Light but I am afraid of performance, My main table of items is average of 10K records" SQL-Express "I am afraid that my POS devices is poor with hardware for SQLExpress, and also hard to install on each device and configure" Less known Advantage Database Server have free distribution of offline ADT system. DBF with extended Library,"Respect for good old DBFs but that era is behind Me with clipper and DBFs" MS Access Sqlite "Mostly like for now, but I am afraid how it is going to pair with MS SQL do they have same Data types". I know that in this SO is a lot of subjective data, but at least can someone recommended some others lite database system, or things that I shod most take attention before I choice database.

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• LEFT OUTER JOIN with a WHERE clause

  - by Wesley

  I have two tables. indRailType contains a list of the names paired with an ID value that I use in other tables to indicate the rail type. WO_BreakerRail contains a date column and a rail code colume that corresponds to the same code in indRailType and some other data. There's a row in WO_BreakerRail for any activity on each rail type, for every date. So I could have 3 rows dated for 3/19/2010, each row indicates a different rail code, and what happened. When I use the following LEFT OUTER JOIN, I get a table with all the types of rail, with nulls in the rows where nothing happened on the 19th. Now, this is only working because I only have one date represented in my WO_BreakerRail table right now, the 19th. When I add more rows with different dates, things will go haywire. This is my SQL statement, which right now gives me exactly the results I want: SELECT WO_BreakerRail.ID, indRailType.RailType, WO_BreakerRail.CreatedPieces, WO_BreakerRail.OutsideSource, WO_BreakerRail.Charged, WO_BreakerRail.Rejected, WO_BreakerRail.RejectedToCrop FROM indRailType LEFT OUTER JOIN WO_BreakerRail ON indRailType.RailCode = WO_BreakerRail.RailCode Now, when I add in a WHERE WO_BreakerRail.Date = @Date clause I lose all the rows in the JOIN which nothing happened. I don't want that. From reading up, it sounds like a FULL OUTER JOIN is what I want, but SQL Server Compact Edition doesn't support FULL OUTER JOINs. Is there a way around this, or am I looking for something else entirely?

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• how to implement a sparse_vector class

  - by Neil G

  I am implementing a templated sparse_vector class. It's like a vector, but it only stores elements that are different from their default constructed value. So, sparse_vector would store the index-value pairs for all indices whose value is not T(). I am basing my implementation on existing sparse vectors in numeric libraries-- though mine will handle non-numeric types T as well. I looked at boost::numeric::ublas::coordinate_vector and eigen::SparseVector. Both store: size_t* indices_; // a dynamic array T* values_; // a dynamic array int size_; int capacity_; Why don't they simply use vector<pair<size_t, T>> data_; My main question is what are the pros and cons of both systems, and which is ultimately better? The vector of pairs manages size_ and capacity_ for you, and simplifies the accompanying iterator classes; it also has one memory block instead of two, so it incurs half the reallocations, and might have better locality of reference. The other solution might search more quickly since the cache lines fill up with only index data during a search. There might also be some alignment advantages if T is an 8-byte type? It seems to me that vector of pairs is the better solution, yet both containers chose the other solution. Why?

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• Properly populating tables in an Object Relational database

  - by chaosTechnician

  I've got a homework assignment that requires that I use Oracle 10g Express to implement an Object Relational database to track phone billing data. I have a superclass of Communications with subclasses of Call, Text, and Data. I'm hitting a snag with properly populating these tables so that I can find the appropriate data in the various tables. My Types and Tables are declared as such: create type CommunicationType as object ( -- column names here ) not final; create type CallType under CommunicationType ( -- column names here ); create type TextType under CommunicationType ( -- column names here ); create type DataType under CommunicationType ( -- column names here ); create table Communications of CommunicationType ( -- Primary and Foreign key constraints here ); create table Calls of CallType; create table Texts of TextType; create table Datas of DataType; When I try to insert data into one of the subclasses, its entry doesn't appear in the superclass. Likewise if I insert into the superclass, it doesn't show up in the appropriate subclass. For example, insert into Calls values (CallType( -- Values -- )); doesn't show any data in Communications. Nor does insert into Communications values (CallType( -- Values -- )); show anything in Calls. What am I doing wrong?

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• What is the best way to return result from business layer to presentation layer when using linq - I

  - by samsur

  I have a business layer that has DTOs that are used in the presentation layer. This application uses entity framework. Here is an example of a class called RoleDTO public class RoleDTO { public Guid RoleId { get; set; } public string RoleName { get; set; } public string RoleDescription { get; set; } public int? OrganizationId { get; set; } } In the BLL I want to have a method that returns a list of DTO.. I would like to know which is the better approach: returning IQueryable or list of DTOs. Although i feel that returning Iqueryable is not a good idea because the connection needs to be open. Here are the 2 different methods using the different approaches public class RoleBLL { private servicedeskEntities sde; public RoleBLL() { sde = new servicedeskEntities(); } public IQueryable<RoleDTO> GetAllRoles() { IQueryable<RoleDTO> role = from r in sde.Roles select new RoleDTO() { RoleId = r.RoleID, RoleName = r.RoleName, RoleDescription = r.RoleDescription, OrganizationId = r.OrganizationId }; return role; } Note: in the above method the datacontext is a private attribute and set in the constructor, so that the connection stays opened. Second approach public static List GetAllRoles() { List roleDTO = new List(); using (servicedeskEntities sde = new servicedeskEntities()) { var roles = from pri in sde.Roles select new { pri.RoleID, pri.RoleName, pri.RoleDescription }; //Add the role entites to the DTO list and return. This is necessary as anonymous types can be returned acrosss methods foreach (var item in roles) { RoleDTO roleItem = new RoleDTO(); roleItem.RoleId = item.RoleID; roleItem.RoleDescription = item.RoleDescription; roleItem.RoleName = item.RoleName; roleDTO.Add(roleItem); } return roleDTO; } Please let me know, if there is a better approach - Thanks,

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• Cocoa Services Programming - How to identify whether the selected item is a folder or file wih NSFi

  - by rockybalboa

  Hi , I have some queries regarding Services menu validation . I would like to enable different services provided by my app based on whether a file or folder is selected in the Finder. I have set NSFilenamesPboardType as the send type for the services . I have gone through the - (id)validRequestorForSendType:(NSString *)sendType returnType:(NSString *)returnType method but my issue is that the validation there seems to be done based on the sendType and return type. In my case , the selected file and folder pasteboard type is the same and I cannot determine whether the selected item in the Finder is a file or folder during the validation process ( This is before the actual service gets invoked i.e when the services menu is being shown to the user ) ? So my question is that is there any way I can get some info about the selected item in the Finder and validate the different service menus offered by my application based on some info regarding the item rather than the basic validation of the send and return types ? I am not able to find out any manner to do so but "Folder Actions" service in Snow Leopard gets enabled only for folders so it can be done. I did a /System/Library/CoreServices/pbs -dump_pboard and it is using a NSFilenamePBoardType also yet manages to activate only for folders. Thanks in advace for any help .

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• Constructor Overloading

  - by Mark Baker

  Normally when I want to create a class constructor that accepts different types of parameters, I'll use a kludgy overloading principle of not defining any args in the constructor definition: e.g. for an ECEF coordinate class constructor, I want it to accept either $x, $y and $z arguments, or to accept a single array argument containg x, y and z values, or to accept a single LatLong object I'd create a constructor looking something like: function __construct() { // Identify if any arguments have been passed to the constructor if (func_num_args() > 0) { $args = func_get_args(); // Identify the overload constructor required, based on the datatype of the first argument $argType = gettype($args[0]); switch($argType) { case 'array' : // Array of Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromArray'; break; case 'object' : // A LatLong object that needs converting to Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromLatLong'; break; default : // Individual Cartesian co-ordinate values $overloadConstructor = 'setCoordinatesFromXYZ'; break; } // Call the appropriate overload constructor call_user_func_array(array($this,$overloadConstructor),$args); } } // function __construct() I'm looking at an alternative: to provide a straight constructor with $x, $y and $z as defined arguments, and to provide static methods of createECEFfromArray() and createECEFfromLatLong() that handle all the necessary extraction of x, y and z; then create a new ECEF object using the standard constructor, and return that Which option is cleaner from an OO purists perspective?

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• How to define multiple elements in XML Schema with the same name and different attribute value allow

  - by David Skyba

  I would like to create XML Schema for this chunk of xml, I would like to restrict the values of "name" attribute, so that in output document on and only one instance of day is allowed for each week day: <a> <day name="monday" /> <day name="tuesday" /> <day name="wednesday" /> </a> I have tried to use this: <xs:complexType name="a"> <xs:sequence> <xs:element name="day" minOccurs="1" maxOccurs="1"> <xs:complexType> <xs:attribute name="name" use="required"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="monday" /> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> <xs:element name="day" minOccurs="1" maxOccurs="1"> <xs:complexType> <xs:attribute name="name" use="required"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="tuesday" /> </xs:restriction> </xs:simpleType> </xs:attribute> </xs:complexType> </xs:element> </xs:sequence> </xs:complexType> but XML Schema validator in eclipse says error "Multiple elements with name 'day', with different types, appear in the model group.". Is there any other way?

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• What is the preferred way in C++ for converting a builtin type (int) to bool?

  - by Martin

  When programming with Visual C++, I think every developer is used to see the warning warning C4800: 'BOOL' : forcing value to bool 'true' or 'false' from time to time. The reason obviously is that BOOL is defined as int and directly assigning any of the built-in numerical types to bool is considered a bad idea. So my question is now, given any built-in numerical type (int, short, ...) that is to be interpreted as a boolean value, what is the/your preferred way of actually storing that value into a variable of type bool? Note: While mixing BOOL and bool is probably a bad idea, I think the problem will inevitably pop up whether on Windows or somewhere else, so I think this question is neither Visual-C++ nor Windows specific. Given int nBoolean; I prefer this style: bool b = nBoolean?true:false; The following might be alternatives: bool b = !!nBoolean; bool b = (nBoolean != 0); Is there a generally preferred way? Rationale? I should add: Since I only work with Visual-C++ I cannot really say if this is a VC++ specific question or if the same problem pops up with other compilers. So it would be interesting to specifically hear from g++ or users how they handle the int-bool case. Regarding Standard C++: As David Thornley notes in a comment, the C++ Standard does not require this behavior. In fact it seems to explicitly allow this, so one might consider this a VC++ weirdness. To quote the N3029 draft (which is what I have around atm.): 4.12 Boolean conversions [conv.bool] A prvalue of arithmetic, unscoped enumeration, pointer, or pointer to member type can be converted to a prvalue of type bool. A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true. (...)

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• Facebook Stream.Get -- How to access data in array?

  - by user316841

  On stream.get, I try to echo $feeds["posts"][$i]["attachment"]["href"]; It return the URL, but, in the same array scope where "type" is located (which returns string: video, etc), trying $feeds["posts"][$i]["attachment"]["type"] returns nothing at all! Here's an array through PHP's var_dump: http://pastie.org/930475 So, from testing I suppose this is protected by Facebook? Does that makes sense at all? Here it's full: http://pastie.org/930490, but not all attachment/media/types has values. It's also strange, because I can't access through [attachment][media][href] or [attachment][media][type], and if I try [attachment][media][0][type] or href, it gives me a string offset error. ["attachment"]=> array(8) { ["media"]=> array(1) { [0]=> array(5) { ["href"]=> string(55) "http://www.facebook.com/video/video.php?v=1392999461587" ["alt"]=> string(13) "IN THE STUDIO" ["type"]=> string(5) "video" My question is, is this protected by Facebook? Or we can actually access this array position?

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• Passing Derived Class Instances as void* to Generic Callbacks in C++

  - by Matthew Iselin

  This is a bit of an involved problem, so I'll do the best I can to explain what's going on. If I miss something, please tell me so I can clarify. We have a callback system where on one side a module or application provides a "Service" and clients can perform actions with this Service (A very rudimentary IPC, basically). For future reference let's say we have some definitions like so: typedef int (*callback)(void*); // This is NOT in our code, but makes explaining easier. installCallback(string serviceName, callback cb); // Really handled by a proper management system sendMessage(string serviceName, void* arg); // arg = value to pass to callback This works fine for basic types such as structs or builtins. We have an MI structure a bit like this: Device <- Disk <- MyDiskProvider class Disk : public virtual Device class MyDiskProvider : public Disk The provider may be anything from a hardware driver to a bit of glue that handles disk images. The point is that classes inherit Disk. We have a "service" which is to be notified of all new Disks in the system, and this is where things unravel: void diskHandler(void *p) { Disk *pDisk = reinterpret_cast<Disk*>(p); // Uh oh! // Remainder is not important } SomeDiskProvider::initialise() { // Probe hardware, whatever... // Tell the disk system we're here! sendMessage("disk-handler", reinterpret_cast<void*>(this)); // Uh oh! } The problem is, SomeDiskProvider inherits Disk, but the callback handler can't receive that type (as the callback function pointer must be generic). Could RTTI and templates help here? Any suggestions would be greatly appreciated.

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• How do you manually set a RadioGroup value in wicket?

  - by Kane

  I'm trying to change the selected radio button in a Wicket RadioGroup during an AjaxEventBehavior but can't figure out how to do so. Specifically when a user types some text in a textbox I want to change the selected radio button to one I specify. How do you do this? Here's what I have so far (it crashes on addComponent): myRadioGroup = new RadioGroup("MyNewGroup", new PropertyModel(getPojo(), "selectedGroup")); Radio internalRadio = new Radio("InternalDirectoryNumber", new Model("Internal")); myRadioGroup .add(internalRadio); Radio externalRadio = new Radio("OtherMobileNumber", new Model("External")); myRadioGroup .add(externalRadio); TextField myTxtField= new TextField("TextBoxPrivateNumber", new PropertyModel(getVoiceItem(), "privateMobilePhone")); myTxtField.add( new AjaxEventBehavior( "onKeyUp" ) { @Override protected void onEvent(AjaxRequestTarget target) { Component component = target.getPage().get("myForm:MyNewGroup").setDefaultModelObject("External"); target.addComponent(component); //this causes an exception } }); myRadioGroup .add(myTxtField); Here is the exception that's thrown. java.lang.IllegalArgumentException: cannot update component that does not have setOutputMarkupId property set to true. Component: [MarkupContainer [Component id = myRadioGroup]] What's the proper way to do this? I'm not finding a whole lot of wicket documentation for this online.

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• Tips on designing a .NET API for future use with F#

  - by Drew Noakes

  I'm in the process of designing a .NET API to allow developers to create RoboCup agents for the 3D simulated soccer league. I'm pretty happy with how the API work with C# code, however I would like to use this project to improve my F# skill (which is currently based on reading rather than practice). So I would like to ask what kinds of things I should consider when designing an API that is to be consumed by both C# and F# code. Some points. I make fairly heavy use of matrix and vector math. These are currently immutable classes/structs. The API currently defines a few interfaces with the consumer implements (eg: IAgent), using instances of their implementations (eg: MyAgent) to construct other API classes (eg: new Client(myAgent)). The API fires events. The API exposes a few delegate types. The API includes several enums. I'd like to release a version of the API as soon as possible and don't want to make major changes to it later if I realise it's too difficult to work with from F#. Any advice is appreciated.

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• Extending the .NET type system so the compiler enforces semantic meaning of primitive values in cert

  - by Drew Noakes

  I'm working with geometry a bit at the moment and am converting a lot between degrees and radians. Unfortunately, both of these are represented by double, so there's compile time warning/error if I try to pass a value in degrees where radians are expected. I believe F# has a compile-time solution for this (called units of measure.) I'd like to do something similar in C#. As another example, imagine a SQL library that accepts various query parameters as strings. It'd be good to have a way of enforcing that only clean strings were allowed to be passed in at runtime, and the only way to get a clean string was to pass through some SQL injection attack preventing logic. The obvious solution is to wrap the double/string/whatever in a new type to give it the type information the compiler needs. I'm curious if anyone has an alternative solution. If you do think wrapping is the only/best way, then please go into some of the downsides of the pattern (and any upsides I haven't mentioned too.) I'm especially concerned about the performance of abstracted primitive numeric types on my calculations at runtime.

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• Question about decorator pattern and the abstract decorator class?

  - by es11

  This question was asked already here, but rather than answering the specific question, descriptions of how the decorator pattern works were given instead. I'd like to ask it again because the answer is not immediately evident to me just by reading how the decorator pattern works (I've read the wikipedia article and the section in the book Head First Design Patterns). Basically, I want to know why an abstract decorator class must be created which implements (or extends) some interface (or abstract class). Why can't all the new "decorated classes" simply implement (or extend) the base abstract object themselves (instead of extending the abstract decorator class)? To make this more concrete I'll use the example from the design patterns book dealing with coffee beverages: There is an abstract component class called Beverage Simple beverage types such as HouseBlend simply extend Beverage To decorate beverage, an abstract CondimentDecorator class is created which extends Beverage and has an instance of Beverage Say we want to add a "milk" condiment, a class Milk is created which extends CondimentDecorator I'd like to understand why we needed the CondimentDecorator class and why the class Milk couldn't have simply extended the Beverage class itself and been passed an instance of Beverage in its constructor. Hopefully this is clear...if not I'd simply like to know why is the abstract decorator class necessary for this pattern? Thanks. Edit: I tried to implement this, omitting the abstract decorator class, and it seems to still work. Is this abstract class present in all descriptions of this pattern simply because it provides a standard interface for all of the new decorated classes?

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