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  • How does Haskell do pattern matching without us defining an Eq on our data types?

    - by devoured elysium
    I have defined a binary tree: data Tree = Null | Node Tree Int Tree and have implemented a function that'll yield the sum of the values of all its nodes: sumOfValues :: Tree -> Int sumOfValues Null = 0 sumOfValues (Node Null v Null) = v sumOfValues (Node Null v t2) = v + (sumOfValues t2) sumOfValues (Node t1 v Null) = v + (sumOfValues t1) sumOfValues (Node t1 v t2) = v + (sumOfValues t1) + (sumOfValues t2) It works as expected. I had the idea of also trying to implement it using guards: sumOfValues2 :: Tree -> Int sumOfValues2 Null = 0 sumOfValues2 (Node t1 v t2) | t1 == Null && t2 == Null = v | t1 == Null = v + (sumOfValues2 t2) | t2 == Null = v + (sumOfValues2 t1) | otherwise = v + (sumOfValues2 t1) + (sumOfValues2 t2) but this one doesn't work because I haven't implemented Eq, I believe: No instance for (Eq Tree) arising from a use of `==' at zzz3.hs:13:3-12 Possible fix: add an instance declaration for (Eq Tree) In the first argument of `(&&)', namely `t1 == Null' In the expression: t1 == Null && t2 == Null In a stmt of a pattern guard for the definition of `sumOfValues2': t1 == Null && t2 == Null The question that has to be made, then, is how can Haskell make pattern matching without knowing when a passed argument matches, without resorting to Eq?

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  • Looking for a full list of jQuery event types.

    - by serg555
    Where I can find a complete list of all jQuery supported events (like click, mouseup etc) with some explanations when they are triggered? I am looking for those that can be binded: $('#foo').bind('click', handler); For example I just found out by accident that there is paste event but I can't find any references to it anywhere in their docs. What else is there?

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  • What is the use of different types of function call in js?

    - by sparrow
    I have seen different type of js function call like function aTestFunction(param) { // function body } and also: aTestFunction = function(param) { // function body } what is the difference in above to implementaion? Also, i found that jquery/prototype js framework uses the second implementation in most cases. Is there any special reason for that? Sorry, I am a novice so this question may be silly to someone but will be helpful me if any guru out there helps me with this silly question. Thanks in advance.

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  • Why does this static factory method involving implied generic types, work?

    - by Cheeso
    Consider public class Tuple<T1, T2> { public Tuple(T1 v1, T2 v2) { V1 = v1; V2 = v2; } public T1 V1 { get; set; } public T2 V2 { get; set; } } public static class Tuple { // MAGIC!! public static Tuple<T1, T2> New<T1, T2>(T1 v1, T2 v2) { return new Tuple<T1, T2>(v1, v2); } } Why does the part labeled "MAGIC" in the above work? It allows syntax like Tuple.New(1, "2") instead of new Tuple<int, string>(1, "2"), but ... how and why? Why do I not need Tuple.New<int,string>(1, "2") ??

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  • Whay types of grammar files are usable for spoken voice recognition?

    - by user1413199
    I'm using the System.Speech library in C# and I would like to create a smaller file to house commands as opposed to the default grammar. I'm not totally sure what I need. I've been looking at several different things but I don't really have any idea what I'm doing. I've read up on some stuff in ANTLR and looked at NuGram from NuEcho. I understand what a grammar file is and roughly how to create one but I'm not sure how they're used specifically for deciphering spoken words.

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  • In Spring MVC, is it possible to have different return types in one request handler method?

    - by Bobo
    For example, if a request succeeds, I will return a View ,if not, return a String indicating error message and set the content-type to either xml or json. Based on what I read, seems like I should use "void" as the return type for handler methods. Check this out: "void if the method handles the response itself (by writing the response content directly, declaring an argument of type ServletResponse / HttpServletResponse for that purpose) or if the view name is supposed to be implicitly determined through a RequestToViewNameTranslator (not declaring a response argument in the handler method signature)."(Spring Framework reference). What I dont understand is what " the view name is supposed to be implicitly determined through a RequestToViewNameTranslator (not declaring a response argument in the handler method signature)" means? Any anyone give me an example?

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  • What types of conditions can be used for conditional compilation in C++?

    - by user1002288
    This is an exam question for C++: Which of the following statements accurately describe the condition that can be used for conditional compilation in C++? A. The condition can depend on the value of environment variables. B. The condition can depend on the value of any const variables. C. The condition can depend on the value of program variables. D. The condition can use the sizeof() operator to make decision about compiler-dependent operations based on the size of standard data type. E. The condition must evaluate to either a 0 or 1 during preprocessing. I think the answer is E. Is this correct?

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  • How to add types from external assembly to toolbox control? (WPF)

    - by Louis Rhys
    I am trying to do something like this in my WPF application: ToolboxControl ctrl = new ToolboxControl(); Assembly assembly = Assembly.LoadFile(file); var category = new ToolboxCategory(assembly.GetName().Name); foreach (Type t in assembly.GetTypes()) { var wrapper = new ToolboxItemWrapper(t, t.Name); category.Add(wrapper); } ctrl.Categories.Add(category); i.e. adding ToolboxItemWrappers for each type found in an assembly. However the last line throws the following exception (see image) All dependencies of the external assembly are also referenced in the main (WPF) application. So what's wrong here and how to fix it?

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  • How can I Find out what BCL types a custom type is using its method?

    - by dotnetdev
    If I have a class, eg T1, and I want to know what classes in the BCL it is using, how could I do this? I came up with this: T1.GetType().GetMethods().Where(x => x.DeclaringType.Namespace == "System"); But this will get all methods in my custom type, but I want to look inside each Method, so I was hoping I could do something like: T1.GetType().GetMethods().BodyTypesUsed; to check if my method uses a type like Streamwriter. How could I achieve this?

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  • Why does the compiler give an ambiguous invocation error when passing inherited types?

    - by Matt Mitchell
    What is happening in the C# compiler to cause the following ambiguous invocation compilation error? The same issue applies to extension methods, or when TestClass is generic and using instance rather than static methods. class Type1 { } class Type2 : Type1 {} class TestClass { public static void Do<T>(T something, object o) where T : Type1 {} public static void Do(Type1 something, string o) {} } void Main() { var firstInstance = new Type1(); TestClass.Do(firstInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(firstInstance, "Test"); // Calls Do<T>(T, string) var secondInstance = new Type2(); TestClass.Do(secondInstance, new object()); // Calls Do(Type1, obj) TestClass.Do(secondInstance, "Test"); // "The call is ambiguous" compile error }

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  • Several different project types in solution use same class. Where can I place this class?

    - by user3605366
    I have one solution with 3 related projects: 1) a Windows console app that reads data and stores it to a mssql DB, 2) WCF service that will retrieve from mssql data, 3) website that will read from the WCF. There could be other projects in the future. The first two projects (and any related future projects) use a Sqlhelper class. Should I create a separate project for it? The most ideal one would be a class library, but I don't know if a WCF invoking a DLL is correct. Any help is appreciated. Thanks.

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  • Declaring two classes that contain instance variables of each others' types.

    - by Benji XVI
    Let’s say you wish to have two classes like so, each declaring an instance variable that is of the other’s class. @interface A : NSObject { B *something; } @end @interface B : NSObject { A *something; } @end It seems to be impossible to declare these classes with these instance variables. In order for A to include an IV of class B, B must already be compiled, and so its @interface must come before A’s. But A’s must be put before B’s for the same reason. Putting the two class declarations in separate files, and #import-ing each other’s .h doesn’t work either, for obvious reasons. So, what is the solution? Or is this either (1) impossible or (2) indicative of a bad design anyway?

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  • How to identify each parameter type in a C# method?

    - by user465876
    I have a C# method say: MyMethod(int num, string name, Color color, MyComplexType complex) Using reflection, how can I distinctly identify each of the parameter types of any method? I want to perform some task by parameter type. If the type is simple int, string or boolean then I do something, if it is Color, XMLDocument, etc I do something else and if it is user defined type like MyComplexType or MyCalci etc then I want to do certain task. I am able to retrieve all the parameters of a method using ParameterInfo and can loop through each parameter and get their types. But how can I identify each data type? foreach (var parameter in parameters) { //identify primitive types?? //identify value types //identify reference types } Edit: this is apart of my code to create a propert grid sort of page where I want to show the parameter list with data types for the selected method. If the parameter has any userdefined type/reference type then I want to expand it further to show all the elements under it with datatypes.

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  • Password Security: Short and Complex versus ‘Short or Lengthy’ and Less Complex

    - by Akemi Iwaya
    Creating secure passwords for our online accounts is a necessary evil due to the huge increase in database and account hacking that occurs these days. The problem though is that no two companies have a similar policy for complex and secure password creation, then factor in the continued creation of insecure passwords or multi-site use of the same password and trouble is just waiting to happen. Ars Technica decided to take a look at multiple password types, how users fared with them, and how well those password types held up to cracking attempts in their latest study. The password types that Ars Technica looked at were comprehensive8, basic8, and basic16. The comprehensive type required a variety of upper-case, lower-case, digits, and symbols with no dictionary words allowed. The only restriction on the two basic types was the number of characters used. Which type do you think was easier for users to adopt and did better in the two password cracking tests? You can learn more about how well users did with the three password types and the results of the tests by visiting the article linked below. What are your thoughts on the matter? Are shorter, more complex passwords better or worse than using short or long, but less complex passwords? What methods do you feel work best since most passwords are limited to approximately 16 characters in length? Perhaps you use a service like LastPass or keep a dedicated list/notebook to manage your passwords. Let us know in the comments!    

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  • Date and Time Support in SQL Server 2008

    - by Aamir Hasan
      Using the New Date and Time Data Types Normal 0 false false false EN-US X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} 1.       The new date and time data types in SQL Server 2008 offer increased range and precision and are ANSI SQL compatible. 2.       Separate date and time data types minimize storage space requirements for applications that need only date or time information. Moreover, the variable precision of the new time data type increases storage savings in exchange for reduced accuracy. 3.       The new data types are mostly compatible with the original date and time data types and use the same Transact-SQL functions. 4.       The datetimeoffset data type allows you to handle date and time information in global applications that use data that originates from different time zones. SELECT c.name, p.* FROM politics pJOIN country cON p.country = c.codeWHERE YEAR(Independence) < 1753ORDER BY IndependenceGO8.    Highlight the SELECT statement and click Execute ( ) to show the use of some of the date functions.T-SQLSELECT c.name AS [Country Name],        CONVERT(VARCHAR(12), p.Independence, 107) AS [Independence Date],       DATEDIFF(YEAR, p.Independence, GETDATE()) AS [Years Independent (appox)],       p.GovernmentFROM politics pJOIN country cON p.country = c.codeWHERE YEAR(Independence) < 1753ORDER BY IndependenceGO10.    Select the SET DATEFORMAT statement and click Execute ( ) to change the DATEFORMAT to day-month-year.T-SQLSET DATEFORMAT dmyGO11.    Select the DECLARE and SELECT statements and click Execute ( ) to show how the datetime and datetime2 data types interpret a date literal.T-SQLSET DATEFORMAT dmyDECLARE @dt datetime = '2008-12-05'DECLARE @dt2 datetime2 = '2008-12-05'SELECT MONTH(@dt) AS [Month-Datetime], DAY(@dt)     AS [Day-Datetime]SELECT MONTH(@dt2) AS [Month-Datetime2], DAY(@dt2)     AS [Day-Datetime2]GO12.    Highlight the DECLARE and SELECT statements and click Execute ( ) to use integer arithmetic on a datetime variable.T-SQLDECLARE @dt datetime = '2008-12-05'SELECT @dt + 1GO13.    Highlight the DECLARE and SELECT statements and click Execute ( ) to show how integer arithmetic is not allowed for datetime2 variables.T-SQLDECLARE @dt2 datetime = '2008-12-05'SELECT @dt2 + 1GO14.    Highlight the DECLARE and SELECT statements and click Execute ( ) to show how to use DATE functions to do simple arithmetic on datetime2 variables.T-SQLDECLARE @dt2 datetime2(7) = '2008-12-05'SELECT DATEADD(d, 1, @dt2)GO15.    Highlight the DECLARE and SELECT statements and click Execute ( ) to show how the GETDATE function can be used with both datetime and datetime2 data types.T-SQLDECLARE @dt datetime = GETDATE();DECLARE @dt2 datetime2(7) = GETDATE();SELECT @dt AS [GetDate-DateTime], @dt2 AS [GetDate-DateTime2]GO16.    Draw attention to the values returned for both columns and how they are equal.17.    Highlight the DECLARE and SELECT statements and click Execute ( ) to show how the SYSDATETIME function can be used with both datetime and datetime2 data types.T-SQLDECLARE @dt datetime = SYSDATETIME();DECLARE @dt2 datetime2(7) = SYSDATETIME();SELECT @dt AS [Sysdatetime-DateTime], @dt2     AS [Sysdatetime-DateTime2]GO18.    Draw attention to the values returned for both columns and how they are different.Programming Global Applications with DateTimeOffset 2.    If you have not previously created the SQLTrainingKitDB database while completing another demo in this training kit, highlight the CREATE DATABASE statement and click Execute ( ) to do so now.T-SQLCREATE DATABASE SQLTrainingKitDBGO3.    Select the USE and CREATE TABLE statements and click Execute ( ) to create table datetest in the SQLTrainingKitDB database.T-SQLUSE SQLTrainingKitDBGOCREATE TABLE datetest (  id integer IDENTITY PRIMARY KEY,  datetimecol datetimeoffset,  EnteredTZ varchar(40)); Reference:http://www.microsoft.com/downloads/details.aspx?FamilyID=E9C68E1B-1E0E-4299-B498-6AB3CA72A6D7&displaylang=en   

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  • Plan your SharePoint 2010 Content Type Hub carefully

    - by Wayne
    Currently setting up a new environment on SharePoint 2010 (which was made available for download yesterday if anyone missed that :-). One of the new features of SharePoint 2010 is to set up a Content Type Hub (which is a part of the Metadata Service Application), which is a hub for all Content Types that other Site Collections can subscribe to. That is you only need to manage your content types in one location. Setting up the Content Type Hub is not that difficult but you must make it very careful to avoid a lot of work and troubleshooting. Here is a short tutorial with a few tips and tricks to make it easy for you to get started. Determine location of Content Type Hub First of all you need to decide in which Site Collection to place your Content Type Hub; in the root site collection or a specific one. I think using a specific Site Collection that only acts as a Content Type Hub is the best way, there are no best practice as of now. So I create a new Site Collection, at for instance http://server/sites/CTH/. The top-level site of this site collection should be for instance a Team Site. You cannot use Blank Site by default, which would have been the best option IMHO, since that site does not have the Taxonomy feature stapled upon it (check the TaxonomyFeatureStapler feature for which site templates that can be used). Configure Managed Metadata Service Application Next you need to create your Managed Metadata Service Application or configure the existing one, Central Administration > Application Management > Manage Service Applications. Select the Managed Metadata service application and click Properties if you already have created it. In the bottom of the dialog window when you are creating the service application or when you are editing the properties is a section to fill in the Content Type Hub. In this text box fill in the URL of the Content Type Hub. It is essential that you have decided where your Content Type Hub will reside, since once this is set you cannot change it. The only way to change it is to rebuild the whole managed metadata service application! Also make sure that you enter the URL correctly. I did copy and paste the URL once and got the /default.aspx in the URL which funked the whole service up. Make sure that you only use the URL to the Site Collection of the hub. Now you have to set up so that other Site Collections can consume the content types from the hub. This is done by selecting the connection for the managed metadata service application and clicking properties. A new dialog window opens and there you need to click the Consumes content types from the Content Type Gallery at nnnn. Now you are free to syndicate your Content Types from the Hub. Publish Content Types To publish a Content Type from the hub you need to go to Site Settings > Content Types and select the content type that you would like to publish. Then select Manage publishing for this content type. This takes you to a page from where you can Publish, Unpublish or Republish the content type. Once the content type is published it can take up to an hour for the subscribing Site Collections to get it. This is controlled by the Content Type Subscriber job that is scheduled to run once an hour. To speed up your publishing just go to Central Administration > Monitoring > Review Job Definitions > Content Type Subscriber and click Run now and you content type is very soon available for use. Published Content Type status You can check the status of the content type publishing in your destination site collections by selecting Site Settings > Content Type Publishing. From here you can force a refresh of all subscribed content types, see which ones that are subscribed and finally check the publishing error log. This error log is very useful for detecting errors during the publishing. For instance if you use any features such as ratings, metadata, document ids in your content type hub and your destination site collection does not have those features available this will be reported here.

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  • CLR via C# 3rd Edition is out

    - by Abhijeet Patel
    Time for some book news update. CLR via C#, 3rd Edition seems to have been out for a little while now. The book was released in early Feb this year, and needless to say my copy is on it’s way. I can barely wait to dig in and chew on the goodies that one of the best technical authors and software professionals I respect has in store. The 2nd edition of the book was an absolute treat and this edition promises to be no less. Here is a brief description of what’s new and updated from the 2nd edition. Part I – CLR Basics Chapter 1-The CLR’s Execution Model Added about discussion about C#’s /optimize and /debug switches and how they relate to each other. Chapter 2-Building, Packaging, Deploying, and Administering Applications and Types Improved discussion about Win32 manifest information and version resource information. Chapter 3-Shared Assemblies and Strongly Named Assemblies Added discussion of TypeForwardedToAttribute and TypeForwardedFromAttribute. Part II – Designing Types Chapter 4-Type Fundamentals No new topics. Chapter 5-Primitive, Reference, and Value Types Enhanced discussion of checked and unchecked code and added discussion of new BigInteger type. Also added discussion of C# 4.0’s dynamic primitive type. Chapter 6-Type and Member Basics No new topics. Chapter 7-Constants and Fields No new topics. Chapter 8-Methods Added discussion of extension methods and partial methods. Chapter 9-Parameters Added discussion of optional/named parameters and implicitly-typed local variables. Chapter 10-Properties Added discussion of automatically-implemented properties, properties and the Visual Studio debugger, object and collection initializers, anonymous types, the System.Tuple type and the ExpandoObject type. Chapter 11-Events Added discussion of events and thread-safety as well as showing a cool extension method to simplify the raising of an event. Chapter 12-Generics Added discussion of delegate and interface generic type argument variance. Chapter 13-Interfaces No new topics. Part III – Essential Types Chapter 14-Chars, Strings, and Working with Text No new topics. Chapter 15-Enums Added coverage of new Enum and Type methods to access enumerated type instances. Chapter 16-Arrays Added new section on initializing array elements. Chapter 17-Delegates Added discussion of using generic delegates to avoid defining new delegate types. Also added discussion of lambda expressions. Chapter 18-Attributes No new topics. Chapter 19-Nullable Value Types Added discussion on performance. Part IV – CLR Facilities Chapter 20-Exception Handling and State Management This chapter has been completely rewritten. It is now about exception handling and state management. It includes discussions of code contracts and constrained execution regions (CERs). It also includes a new section on trade-offs between writing productive code and reliable code. Chapter 21-Automatic Memory Management Added discussion of C#’s fixed state and how it works to pin objects in the heap. Rewrote the code for weak delegates so you can use them with any class that exposes an event (the class doesn’t have to support weak delegates itself). Added discussion on the new ConditionalWeakTable class, GC Collection modes, Full GC notifications, garbage collection modes and latency modes. I also include a new sample showing how your application can receive notifications whenever Generation 0 or 2 collections occur. Chapter 22-CLR Hosting and AppDomains Added discussion of side-by-side support allowing multiple CLRs to be loaded in a single process. Added section on the performance of using MarshalByRefObject-derived types. Substantially rewrote the section on cross-AppDomain communication. Added section on AppDomain Monitoring and first chance exception notifications. Updated the section on the AppDomainManager class. Chapter 23-Assembly Loading and Reflection Added section on how to deploy a single file with dependent assemblies embedded inside it. Added section comparing reflection invoke vs bind/invoke vs bind/create delegate/invoke vs C#’s dynamic type. Chapter 24-Runtime Serialization This is a whole new chapter that was not in the 2nd Edition. Part V – Threading Chapter 25-Threading Basics Whole new chapter motivating why Windows supports threads, thread overhead, CPU trends, NUMA Architectures, the relationship between CLR threads and Windows threads, the Thread class, reasons to use threads, thread scheduling and priorities, foreground thread vs background threads. Chapter 26-Performing Compute-Bound Asynchronous Operations Whole new chapter explaining the CLR’s thread pool. This chapter covers all the new .NET 4.0 constructs including cooperative cancelation, Tasks, the aralle class, parallel language integrated query, timers, how the thread pool manages its threads, cache lines and false sharing. Chapter 27-Performing I/O-Bound Asynchronous Operations Whole new chapter explaining how Windows performs synchronous and asynchronous I/O operations. Then, I go into the CLR’s Asynchronous Programming Model, my AsyncEnumerator class, the APM and exceptions, Applications and their threading models, implementing a service asynchronously, the APM and Compute-bound operations, APM considerations, I/O request priorities, converting the APM to a Task, the event-based Asynchronous Pattern, programming model soup. Chapter 28-Primitive Thread Synchronization Constructs Whole new chapter discusses class libraries and thread safety, primitive user-mode, kernel-mode constructs, and data alignment. Chapter 29-Hybrid Thread Synchronization Constructs Whole new chapter discussion various hybrid constructs such as ManualResetEventSlim, SemaphoreSlim, CountdownEvent, Barrier, ReaderWriterLock(Slim), OneManyResourceLock, Monitor, 3 ways to solve the double-check locking technique, .NET 4.0’s Lazy and LazyInitializer classes, the condition variable pattern, .NET 4.0’s concurrent collection classes, the ReaderWriterGate and SyncGate classes.

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  • C#/.NET Little Wonders: Fun With Enum Methods

    - by James Michael Hare
    Once again lets dive into the Little Wonders of .NET, those small things in the .NET languages and BCL classes that make development easier by increasing readability, maintainability, and/or performance. So probably every one of us has used an enumerated type at one time or another in a C# program.  The enumerated types we create are a great way to represent that a value can be one of a set of discrete values (or a combination of those values in the case of bit flags). But the power of enum types go far beyond simple assignment and comparison, there are many methods in the Enum class (that all enum types “inherit” from) that can give you even more power when dealing with them. IsDefined() – check if a given value exists in the enum Are you reading a value for an enum from a data source, but are unsure if it is actually a valid value or not?  Casting won’t tell you this, and Parse() isn’t guaranteed to balk either if you give it an int or a combination of flags.  So what can we do? Let’s assume we have a small enum like this for result codes we want to return back from our business logic layer: 1: public enum ResultCode 2: { 3: Success, 4: Warning, 5: Error 6: } In this enum, Success will be zero (unless given another value explicitly), Warning will be one, and Error will be two. So what happens if we have code like this where perhaps we’re getting the result code from another data source (could be database, could be web service, etc)? 1: public ResultCode PerformAction() 2: { 3: // set up and call some method that returns an int. 4: int result = ResultCodeFromDataSource(); 5:  6: // this will suceed even if result is < 0 or > 2. 7: return (ResultCode) result; 8: } So what happens if result is –1 or 4?  Well, the cast does not fail, so what we end up with would be an instance of a ResultCode that would have a value that’s outside of the bounds of the enum constants we defined. This means if you had a block of code like: 1: switch (result) 2: { 3: case ResultType.Success: 4: // do success stuff 5: break; 6:  7: case ResultType.Warning: 8: // do warning stuff 9: break; 10:  11: case ResultType.Error: 12: // do error stuff 13: break; 14: } That you would hit none of these blocks (which is a good argument for always having a default in a switch by the way). So what can you do?  Well, there is a handy static method called IsDefined() on the Enum class which will tell you if an enum value is defined.  1: public ResultCode PerformAction() 2: { 3: int result = ResultCodeFromDataSource(); 4:  5: if (!Enum.IsDefined(typeof(ResultCode), result)) 6: { 7: throw new InvalidOperationException("Enum out of range."); 8: } 9:  10: return (ResultCode) result; 11: } In fact, this is often recommended after you Parse() or cast a value to an enum as there are ways for values to get past these methods that may not be defined. If you don’t like the syntax of passing in the type of the enum, you could clean it up a bit by creating an extension method instead that would allow you to call IsDefined() off any isntance of the enum: 1: public static class EnumExtensions 2: { 3: // helper method that tells you if an enum value is defined for it's enumeration 4: public static bool IsDefined(this Enum value) 5: { 6: return Enum.IsDefined(value.GetType(), value); 7: } 8: }   HasFlag() – an easier way to see if a bit (or bits) are set Most of us who came from the land of C programming have had to deal extensively with bit flags many times in our lives.  As such, using bit flags may be almost second nature (for a quick refresher on bit flags in enum types see one of my old posts here). However, in higher-level languages like C#, the need to manipulate individual bit flags is somewhat diminished, and the code to check for bit flag enum values may be obvious to an advanced developer but cryptic to a novice developer. For example, let’s say you have an enum for a messaging platform that contains bit flags: 1: // usually, we pluralize flags enum type names 2: [Flags] 3: public enum MessagingOptions 4: { 5: None = 0, 6: Buffered = 0x01, 7: Persistent = 0x02, 8: Durable = 0x04, 9: Broadcast = 0x08 10: } We can combine these bit flags using the bitwise OR operator (the ‘|’ pipe character): 1: // combine bit flags using 2: var myMessenger = new Messenger(MessagingOptions.Buffered | MessagingOptions.Broadcast); Now, if we wanted to check the flags, we’d have to test then using the bit-wise AND operator (the ‘&’ character): 1: if ((options & MessagingOptions.Buffered) == MessagingOptions.Buffered) 2: { 3: // do code to set up buffering... 4: // ... 5: } While the ‘|’ for combining flags is easy enough to read for advanced developers, the ‘&’ test tends to be easy for novice developers to get wrong.  First of all you have to AND the flag combination with the value, and then typically you should test against the flag combination itself (and not just for a non-zero)!  This is because the flag combination you are testing with may combine multiple bits, in which case if only one bit is set, the result will be non-zero but not necessarily all desired bits! Thanks goodness in .NET 4.0 they gave us the HasFlag() method.  This method can be called from an enum instance to test to see if a flag is set, and best of all you can avoid writing the bit wise logic yourself.  Not to mention it will be more readable to a novice developer as well: 1: if (options.HasFlag(MessagingOptions.Buffered)) 2: { 3: // do code to set up buffering... 4: // ... 5: } It is much more concise and unambiguous, thus increasing your maintainability and readability. It would be nice to have a corresponding SetFlag() method, but unfortunately generic types don’t allow you to specialize on Enum, which makes it a bit more difficult.  It can be done but you have to do some conversions to numeric and then back to the enum which makes it less of a payoff than having the HasFlag() method.  But if you want to create it for symmetry, it would look something like this: 1: public static T SetFlag<T>(this Enum value, T flags) 2: { 3: if (!value.GetType().IsEquivalentTo(typeof(T))) 4: { 5: throw new ArgumentException("Enum value and flags types don't match."); 6: } 7:  8: // yes this is ugly, but unfortunately we need to use an intermediate boxing cast 9: return (T)Enum.ToObject(typeof (T), Convert.ToUInt64(value) | Convert.ToUInt64(flags)); 10: } Note that since the enum types are value types, we need to assign the result to something (much like string.Trim()).  Also, you could chain several SetFlag() operations together or create one that takes a variable arg list if desired. Parse() and ToString() – transitioning from string to enum and back Sometimes, you may want to be able to parse an enum from a string or convert it to a string - Enum has methods built in to let you do this.  Now, many may already know this, but may not appreciate how much power are in these two methods. For example, if you want to parse a string as an enum, it’s easy and works just like you’d expect from the numeric types: 1: string optionsString = "Persistent"; 2:  3: // can use Enum.Parse, which throws if finds something it doesn't like... 4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result == MessagingOptions.Persistent) 7: { 8: Console.WriteLine("It worked!"); 9: } Note that Enum.Parse() will throw if it finds a value it doesn’t like.  But the values it likes are fairly flexible!  You can pass in a single value, or a comma separated list of values for flags and it will parse them all and set all bits: 1: // for string values, can have one, or comma separated. 2: string optionsString = "Persistent, Buffered"; 3:  4: var result = (MessagingOptions)Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked!"); 9: } Or you can parse in a string containing a number that represents a single value or combination of values to set: 1: // 3 is the combination of Buffered (0x01) and Persistent (0x02) 2: var optionsString = "3"; 3:  4: var result = (MessagingOptions) Enum.Parse(typeof (MessagingOptions), optionsString); 5:  6: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 7: { 8: Console.WriteLine("It worked again!"); 9: } And, if you really aren’t sure if the parse will work, and don’t want to handle an exception, you can use TryParse() instead: 1: string optionsString = "Persistent, Buffered"; 2: MessagingOptions result; 3:  4: // try parse returns true if successful, and takes an out parm for the result 5: if (Enum.TryParse(optionsString, out result)) 6: { 7: if (result.HasFlag(MessagingOptions.Persistent) && result.HasFlag(MessagingOptions.Buffered)) 8: { 9: Console.WriteLine("It worked!"); 10: } 11: } So we covered parsing a string to an enum, what about reversing that and converting an enum to a string?  The ToString() method is the obvious and most basic choice for most of us, but did you know you can pass a format string for enum types that dictate how they are written as a string?: 1: MessagingOptions value = MessagingOptions.Buffered | MessagingOptions.Persistent; 2:  3: // general format, which is the default, 4: Console.WriteLine("Default : " + value); 5: Console.WriteLine("G (default): " + value.ToString("G")); 6:  7: // Flags format, even if type does not have Flags attribute. 8: Console.WriteLine("F (flags) : " + value.ToString("F")); 9:  10: // integer format, value as number. 11: Console.WriteLine("D (num) : " + value.ToString("D")); 12:  13: // hex format, value as hex 14: Console.WriteLine("X (hex) : " + value.ToString("X")); Which displays: 1: Default : Buffered, Persistent 2: G (default): Buffered, Persistent 3: F (flags) : Buffered, Persistent 4: D (num) : 3 5: X (hex) : 00000003 Now, you may not really see a difference here between G and F because I used a [Flags] enum, the difference is that the “F” option treats the enum as if it were flags even if the [Flags] attribute is not present.  Let’s take a non-flags enum like the ResultCode used earlier: 1: // yes, we can do this even if it is not [Flags] enum. 2: ResultCode value = ResultCode.Warning | ResultCode.Error; And if we run that through the same formats again we get: 1: Default : 3 2: G (default): 3 3: F (flags) : Warning, Error 4: D (num) : 3 5: X (hex) : 00000003 Notice that since we had multiple values combined, but it was not a [Flags] marked enum, the G and default format gave us a number instead of a value name.  This is because the value was not a valid single-value constant of the enum.  However, using the F flags format string, it broke out the value into its component flags even though it wasn’t marked [Flags]. So, if you want to get an enum to display appropriately for whether or not it has the [Flags] attribute, use G which is the default.  If you always want it to attempt to break down the flags, use F.  For numeric output, obviously D or  X are the best choice depending on whether you want decimal or hex. Summary Hopefully, you learned a couple of new tricks with using the Enum class today!  I’ll add more little wonders as I think of them and thanks for all the invaluable input!   Technorati Tags: C#,.NET,Little Wonders,Enum,BlackRabbitCoder

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  • Using Umbraco&rsquo;s Dropdown Datatype

    - by MightyZot
    In Umbraco, you could consider document types like models and data types as property types for those modes. For example, you may create a document type called “Prices” to represent a page that displays a list of prices. And, then, you might create a document type called “Price Item” to represent the price list items. A property called “Price” could then represent the price of an item. When you create the Price property, you specify the data type, which in this case might be “Number”, indicating that this particular field accepts only numerical values. Consequently, you could also create a drop down list property called “Category”, allowing you to categorize the items in your price list. To add items to the drop down list, you modify the data type definition in the Developer module of the Umbraco administrative utility. Instead of modifying the drop down data type itself, you should first make a copy by right-clicking on the Data Types node and choosing Create. Give your new data type a name in the Create dialog and click the Create button. In the Edit datatype dialog, change “Render control” to “Dropdown list”.  To add your list items, simply enter that value into the textbox next to “Add prevalue” and click Save or press the Enter key. Now that you have a new drop down list data type created, along with assigned list items, you can use it in your document type definitions just like you would the other data types.

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