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  • Higher-kinded Types with C++

    - by Venkat Shiva
    This question is for the people who know both Haskell (or any other functional language that supports Higher-kinded Types) and C++... Is it possible to model higher kinded types using C++ templates? If yes, then how?

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  • How can I enable anonymous access to a Samba share under ADS security mode?

    - by hemp
    I'm trying to enable anonymous access to a single service in my Samba config. Authorized user access is working perfectly, but when I attempt a no-password connection, I get this message: Anonymous login successful Domain=[...] OS=[Unix] Server=[Samba 3.3.8-0.51.el5] tree connect failed: NT_STATUS_LOGON_FAILURE The message log shows this error: ... smbd[21262]: [2010/05/24 21:26:39, 0] smbd/service.c:make_connection_snum(1004) ... smbd[21262]: Can't become connected user! The smb.conf is configured thusly: [global] security = ads obey pam restrictions = Yes winbind enum users = Yes winbind enum groups = Yes winbind use default domain = true valid users = "@domain admins", "@domain users" guest account = nobody map to guest = Bad User [evilshare] path = /evil/share guest ok = yes read only = No browseable = No Given that I have 'map to guest = Bad User' and 'guest ok' specified, I don't understand why it is trying to "become connected user". Should it not be trying to "become guest user"?

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  • Is there any functional difference between immutable value types and immutable reference types?

    - by Kendall Frey
    Value types are types which do not have an identity. When one variable is modified, other instances are not. Using Javascript syntax as an example, here is how a value type works. var foo = { a: 42 }; var bar = foo; bar.a = 0; // foo.a is still 42 Reference types are types which do have an identity. When one variable is modified, other instances are as well. Here is how a reference type works. var foo = { a: 42 }; var bar = foo; bar.a = 0; // foo.a is now 0 Note how the example uses mutatable objects to show the difference. If the objects were immutable, you couldn't do that, so that kind of testing for value/reference types doesn't work. Is there any functional difference between immutable value types and immutable reference types? Is there any algorithm that can tell the difference between a reference type and a value type if they are immutable? Reflection is cheating. I'm wondering this mostly out of curiosity.

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  • Nullable types and ?? operator C# [en-US]

    - by ruimachado
    Nullable types vs Non-nullable types   While developing our C# projects its frequent the null comparison operation to avoid null exceptions. This simple operation is mainly coded using the "var x = null" code example inside an if clause. However not all types of variables are nullable, which means that setting a variable to null is not allowed in every cases, it depends on what kind of type are you defining. But what if there was an extension to your non-nullable type that would convert your variable types to nullable? This extension really exists. As I said before in C# you have nullable types which represent all the values of an underlying type, and an additional null value and can be declared easily using "T?", where T is the type of the variable and for example the normal int type cannot be null, so its a non-nullable type, however if you define a "int?" your variable can be null, what you do is convert a non-nullable type to a nullable type. Example: int x=null;     Not allowed     int? x=null;   Allowed     While using nullable types you can check if a variable is null the same way you do it with nullable types:     But what about setting a default value when a certain variable is null?   In this cases the c# .net framework let you set a default value when you try to assign a nullable type to a non-nullable type, using the ?? operator. If you don't use this operator you can still catch the InvalidOperationException which is throw in this cases. For example  without the ?? operator :     Using the ?? operator your code becomes cleaner and more easy to read and you get a bonus, you can set a default value for multiple variables using the ?? in a chain set.     That’s it,   Thanks, Rui Machado rpmachado.wordpress.com

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  • C++ Types Impossible to Name

    - by Kirakun
    While reading Wikipedia's page on decltype, I was curious about the statement, Its [decltype's] primary intended use is in generic programming, where it is often difficult, or even impossible, to name types that depend on template parameters. While I can understand the difficulty part of that statement, what is an example where there is a need to name a type that cannot be named under C++03? EDIT: My point is that since everything in C++ has a declaration of types. Why would there ever be a case where it is impossible to name a type? Furthermore, aren't trait classes designed to yield type informations? Could trait classes be an alternative to decltype?

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  • C#: Get key and value types of non-generic IDictionary at runtime

    - by Yang Zou
    there. I am wondering how I can get the key and value types of a non-generic IDictionary at runtime. For generic IDictionary, we can use reflection to get the generic arguments, which has been answered here. But for non-generic IDictionary, for instance, HybridDictionary, how can I get the key and value types? Thanks. Edit: I may not describe my problem properly. For non-generic IDictionary, if I have HyBridDictionary, which is declared as HyBridDictionary dict = new HyBridDictionary(); dict.Add("foo" , 1); dict.Add("bar", 2); How can I find out the type of the key is string and type of the value is int? Did I make the question clear? Thanks.

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  • assembly.GetTypes() does not return all types

    - by meta
    I try to lead the types from an .dll (which is also referenced in the executing project). I call: public static void LoadPlugin(string pluginFile) { Assembly assembly = Assembly.LoadFrom(pluginFile); foreach (Type type in assembly.GetTypes()) { // play with it } } It loads just a few of them: public partial class Mathematics : UserControl, IMathematics, IPortable and public partial class Welcome : UserControl but the next one, and some others, are ignored: public partial class Test : UserControl, ITest, IPortable They all stand in the same assembly, under the same namespace. The public static void LoadPlugin(string pluginFile) method is located in other assembly that is also referenced in the executing project. No exceptions are thrown. What could be the issues for not loading all the types? Any ideas?

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  • f# types' properties in inconsistent order and of slightly differing types

    - by philbrowndotcom
    I'm trying to iterate through an array of objects and recursively print out each objects properties. Here is my object model: type firmIdentifier = { firmId: int ; firmName: string ; } type authorIdentifier = { authorId: int ; authorName: string ; firm: firmIdentifier ; } type denormalizedSuggestedTradeRecommendations = { id: int ; ticker: string ; direction: string ; author: authorIdentifier ; } Here is how I am instantiating my objects: let getMyIdeasIdeas = [| {id=1; ticker="msfqt"; direction="buy"; author={authorId=0; authorName="john Smith"; firm={firmId=12; firmName="Firm1"}};}; {id=2; ticker="goog"; direction="sell"; author={authorId=1; authorName="Bill Jones"; firm={firmId=13; firmName="ABC Financial"}};}; {id=3; ticker="DFHF"; direction="buy"; author={authorId=2; authorName="Ron James"; firm={firmId=2; firmName="DEFFirm"}};}|] And here is my algorithm to iterate, recurse and print: let rec recurseObj (sb : StringBuilder) o= let props : PropertyInfo [] = o.GetType().GetProperties() sb.Append( o.GetType().ToString()) |> ignore for x in props do let getMethod = x.GetGetMethod() let value = getMethod.Invoke(o, Array.empty) ignore <| match value with | :? float | :? int | :? string | :? bool as f -> sb.Append(x.Name + ": " + f.ToString() + "," ) |> ignore | _ -> recurseObj sb value for x in getMyIdeas do recurseObj sb x sb.Append("\r\n") |> ignore If you couldnt tell, I'm trying to create a csv file and am printing out the types for debugging purposes. The problem is, the first element comes through in the order you'd expect, but all subsequent elements come through with a slightly different (and confusing) ordering of the "child" properties like so: RpcMethods+denormalizedSuggestedTradeRecommendationsid: 1,ticker: msfqt,direction: buy,RpcMethods+authorIdentifierauthorId: 0,authorName: john Smith,RpcMethods+firmIdentifierfirmId: 12,firmName: Firm1, RpcMethods+denormalizedSuggestedTradeRecommendationsid: 2,ticker: goog,direction: sell,RpcMethods+authorIdentifierauthorName: Bill Jones,RpcMethods+firmIdentifierfirmName: ABC Financial,firmId: 13,authorId: 1, RpcMethods+denormalizedSuggestedTradeRecommendationsid: 3,ticker: DFHF,direction: buy,RpcMethods+authorIdentifierauthorName: Ron James,RpcMethods+firmIdentifierfirmName: DEFFirm,firmId: 2,authorId: 2, Any idea what is going on here?

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  • Using SQL Developer to Debug your Anonymous PL/SQL Blocks

    - by JeffS
    Everyone knows that SQL Developer has a PL/SQL debugger – check! Everyone also knows that it’s only setup for debugging standalone PL/SQL objects like Functions, Procedures, and Packages, right? – NO! SQL Developer can also debug your Stored Java Procedures AND it can debug your standalone PLSQL blocks. These bits of PLSQL which do not live in the database are also known as ‘Anonymous Blocks.’ Anonymous PL/SQL blocks can be submitted to interactive tools such as SQL*Plus and Enterprise Manager, or embedded in an Oracle Precompiler or OCI program. At run time, the program sends these blocks to the Oracle database, where they are compiled and executed. Here’s an example of something you might want help debugging: Declare x number := 0; Begin Dbms_Output.Put(Sysdate || ' ' || Systimestamp); For Stuff In 1..100 Loop Dbms_Output.Put_Line('Stuff is equal to ' || Stuff || '.'); x := Stuff; End Loop; End; / With the power of remote debugging and unshared worksheets, we are going to be able to debug this ANON block! The trick – we need to create a dummy stored procedure and call it in our ANON block. Then we’re going to create an unshared worksheet and execute the script from there while the SQL Developer session is listening for remote debug connections. We step through the dummy procedure, and this takes OUT to our calling ANON block. Then we can use watches, breakpoints, and all that fancy debugger stuff! First things first, create this dummy procedure - create or replace procedure do_nothing is begin null; end; Then mouse-right-click on your Connection and select ‘Remote Debug.’ For an in-depth post on how to use the remote debugger, check out Barry’s excellent post on the subject. Open an unshared worksheet using Ctrl+Shift+N. This gives us a dedicated connection for our worksheet and any scripts or commands executed in it. Paste in your ANON block you want to debug. Add in a call to the dummy procedure above to the first line of your BEGIN block like so Begin do_nothing(); ... Then we need to setup the machine for remote debug for the session we have listening – basically we connect to SQL Developer. You can do that via a Environment Variable, or you can just add this line to your script - CALL DBMS_DEBUG_JDWP.CONNECT_TCP( 'localhost', '4000' ); Where ‘localhost’ is the machine where SQL Developer is running and ’4000′ is the port you started the debug listener on. Ok, with that all set, now just RUN the script. Once the PL/SQL call is made, the debugger will be invoked. You’ll end up in the DO_NOTHING() object. Debugging an ANON block from SQL Developer is possible! If you step out to the ANON block, we’ll end up in the script that’s used to call the procedure – which is the script you want to debug. The Anonymous Block is opened in a new SQL Dev page You can now step through the block, using watches and breakpoints as expected. I’m guessing your scripts are going to be a bit more complicated than mine, but this serves as a decent example to get you started. Here’s a screenshot of a watch and breakpoint defined in the anon block being debugged: Breakpoints, watches, and callstacks - oh my! For giggles, I created a breakpoint with a passcount of 90 for the FOR LOOP to see if it works. And of course it does You Might Also EnjoyUsing Pass Counts to Turbo Charge Your PL/SQL BreakpointsSQL Developer Tip: Viewing REFCURSOR OutputThe PL/SQL Debugger Strikes Back: Episode VDebugging PL/SQL with SQL Developer: Episode IVHow to find dependent objects in your PL/SQL Programs using SQL Developer

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  • Instantiating a list of parameterized types, making beter use of Generics and Linq

    - by DanO
    I'm hashing a file with one or more hash algorithms. When I tried to parametrize which hash types I want, it got a lot messier than I was hoping. I think I'm missing a chance to make better use of generics or LINQ. I also don't like that I have to use a Type[] as the parameter instead of limiting it to a more specific set of type (HashAlgorithm descendants), I'd like to specify types as the parameter and let this method do the constructing, but maybe this would look better if I had the caller new-up instances of HashAlgorithm to pass in? public List<string> ComputeMultipleHashesOnFile(string filename, Type[] hashClassTypes) { var hashClassInstances = new List<HashAlgorithm>(); var cryptoStreams = new List<CryptoStream>(); FileStream fs = File.OpenRead(filename); Stream cryptoStream = fs; foreach (var hashClassType in hashClassTypes) { object obj = Activator.CreateInstance(hashClassType); var cs = new CryptoStream(cryptoStream, (HashAlgorithm)obj, CryptoStreamMode.Read); hashClassInstances.Add((HashAlgorithm)obj); cryptoStreams.Add(cs); cryptoStream = cs; } CryptoStream cs1 = cryptoStreams.Last(); byte[] scratch = new byte[1 << 16]; int bytesRead; do { bytesRead = cs1.Read(scratch, 0, scratch.Length); } while (bytesRead > 0); foreach (var stream in cryptoStreams) { stream.Close(); } foreach (var hashClassInstance in hashClassInstances) { Console.WriteLine("{0} hash = {1}", hashClassInstance.ToString(), HexStr(hashClassInstance.Hash).ToLower()); } }

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  • C# 4: Real-World Example of Dynamic Types

    - by routeNpingme
    I think I have my brain halfway wrapped around the Dynamic Types concept in C# 4, but can't for the life of me figure out a scenario where I'd actually want to use it. I'm sure there are many, but I'm just having trouble making the connection as to how I could engineer a solution that is better solved with dynamics as opposed to interfaces, dependency injection, etc. So, what's a real-world application scenario where dynamic type usage is appropriate?

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  • Unpacking tuple types in Scala

    - by jpalecek
    I was just wondering, can I decompose a tuple type into its components' types in Scala? I mean, something like this trait Container { type Element } trait AssociativeContainer extends Container { type Element <: (Unit, Unit) def get(x : Element#First) : Element#Second }

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  • Design Patterns : Question about "Types"

    - by contactmatt
    Would someone please explain to me what the below paragraph means? This is a snippet from "Design Patterns: Elements of Reusable OO software" Part of an object's interface may be characterized by one type, and other parts by other types. Two objects of the same type need only share parts of their interfaces. Interfaces can contain other interfaces as subsets. - Design Patterns - Elements of Reusable OO software, pg 13

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  • Determining if types alias to the same underlying type in C++

    - by emchristiansen
    I'd like to write a templated function which changes its behavior depending on template class types passed in. To do this, I'd like to determine the type passed in. For example, something like this: template <class T> void foo() { if (T == int) { // Sadly, this sort of comparison doesn't work printf("Template parameter was int\n"); } else if (T == char) { printf("Template parameter was char\n"); } } Is this possible?

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  • Describing Types question

    - by user288245
    I have a bunch of types (eg. LargePlane, SmallPlane) that could be in this collection i've made, how do i print like LargePlane? I've tried like typeOf() and stuff but it doesn't work. Within like a toString()? So when i output the collection it states what type it is.

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  • How to get aspnet_Users.UserId for an anonymous user in ASP.NET membership ?

    - by Simon_Weaver
    I am trying to get the aspnet membership UserId field from an anonymous user. I have enabled anonymous identification in web.config : <anonymousIdentification enabled="true" /> I have also created a profile: <profile> <providers> <clear /> <add name="AspNetSqlProfileProvider" type="System.Web.Profile.SqlProfileProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" connectionStringName="ApplicationServices" applicationName="/" /> </providers> <properties> <add name="Email" type="System.String" allowAnonymous="true"/> <add name="SomethingElse" type="System.Int32" allowAnonymous="true"/> </properties> </profile> I see data in my aspnetdb\aspnet_Users table for anonymous users that have had profile information set. Userid PropertyNames PropertyValuesString 36139818-4245-45dd-99cb-2a721d43f9c5 Email:S:0:17: [email protected] I just need to find how to get the 'Userid' value. It is not possible to use : Membership.Provider.GetUser(Request.AnonymousID, false); The Request.AnonymousID is a different GUID and not equal to 36139818-4245-45dd-99cb-2a721d43f9c5. Is there any way to get this Userid. I want to associate it with incomplete activity for an anonymous user. Using the primary key of aspnet_Users is preferable to having to create my own GUID (which I could do and store in the profile). This is basically a dupe of this question but the question was never actually answered.

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  • Performance surprise with "as" and nullable types

    - by Jon Skeet
    I'm just revising chapter 4 of C# in Depth which deals with nullable types, and I'm adding a section about using the "as" operator, which allows you to write: object o = ...; int? x = o as int?; if (x.HasValue) { ... // Use x.Value in here } I thought this was really neat, and that it could improve performance over the C# 1 equivalent, using "is" followed by a cast - after all, this way we only need to ask for dynamic type checking once, and then a simple value check. This appears not to be the case, however. I've included a sample test app below, which basically sums all the integers within an object array - but the array contains a lot of null references and string references as well as boxed integers. The benchmark measures the code you'd have to use in C# 1, the code using the "as" operator, and just for kicks a LINQ solution. To my astonishment, the C# 1 code is 20 times faster in this case - and even the LINQ code (which I'd have expected to be slower, given the iterators involved) beats the "as" code. Is the .NET implementation of isinst for nullable types just really slow? Is it the additional unbox.any that causes the problem? Is there another explanation for this? At the moment it feels like I'm going to have to include a warning against using this in performance sensitive situations... Results: Cast: 10000000 : 121 As: 10000000 : 2211 LINQ: 10000000 : 2143 Code: using System; using System.Diagnostics; using System.Linq; class Test { const int Size = 30000000; static void Main() { object[] values = new object[Size]; for (int i = 0; i < Size - 2; i += 3) { values[i] = null; values[i+1] = ""; values[i+2] = 1; } FindSumWithCast(values); FindSumWithAs(values); FindSumWithLinq(values); } static void FindSumWithCast(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { if (o is int) { int x = (int) o; sum += x; } } sw.Stop(); Console.WriteLine("Cast: {0} : {1}", sum, (long) sw.ElapsedMilliseconds); } static void FindSumWithAs(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = 0; foreach (object o in values) { int? x = o as int?; if (x.HasValue) { sum += x.Value; } } sw.Stop(); Console.WriteLine("As: {0} : {1}", sum, (long) sw.ElapsedMilliseconds); } static void FindSumWithLinq(object[] values) { Stopwatch sw = Stopwatch.StartNew(); int sum = values.OfType<int>().Sum(); sw.Stop(); Console.WriteLine("LINQ: {0} : {1}", sum, (long) sw.ElapsedMilliseconds); } }

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  • How to compare nullable types?

    - by David_001
    I have a few places where I need to compare 2 (nullable) values, to see if they're the same. I think there should be something in the framework to support this, but can't find anything, so instead have the following: public static bool IsDifferentTo(this bool? x, bool? y) { return (x.HasValue != y.HasValue) ? true : x.HasValue && x.Value != y.Value; } Then, within code I have if (x.IsDifferentTo(y)) ... I then have similar methods for nullable ints, nullable doubles etc. Is there not an easier way to see if two nullable types are the same? Update: Turns out that the reason this method existed was because the code has been converted from VB.Net, where Nothing = Nothing returns false (compare to C# where null == null returns true). The VB.Net code should have used .Equals... instead.

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  • Why shouldn't I always use nullable types in C#.

    - by Matthew Vines
    I've been searching for some good guidance on this since the concept was introduced in .net 2.0. Why would I ever want to use non-nullable data types in c#? (A better question is why wouldn't I choose nullable types by default, and only use non-nullable types when that explicitly makes sense.) Is there a 'significant' performance hit to choosing a nullable data type over its non-nullable peer? I much prefer to check my values against null instead of Guid.empty, string.empty, DateTime.MinValue,<= 0, etc, and to work with nullable types in general. And the only reason I don't choose nullable types more often is the itchy feeling in the back of my head that makes me feel like it's more than backwards compatibility that forces that extra '?' character to explicitly allow a null value. Is there anybody out there that always (most always) chooses nullable types rather than non-nullable types? Thanks for your time,

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  • How to aggregate over few types with linq?

    - by Shimmy
    Can someone help me translate the following to one liner: Dim items As New List(Of Object) For Each c In ph.Contacts items.Add(New With {.Type = "Contact", .Id = c.ContactId, .Title = c.Title}) Next For Each c In ph.Persons items.Add(New With {.Type = "Person", .Id = c.PersonId, .Title = c.Title}) Next For Each c In ph.Jobs items.Add(New With {.Type = "Job", .Id = c.JobId, .Title = c.Title}) Next Is it possible to merge them all into one query or method line, I don't really care if this will be done with something other than linq, I am just looking for a more efficient way as I have a long list coming ahead, and the aggregating list will be strongly-typed using Dim list = blah blah

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