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  • C# style Action<T>, Func<T,T>, etc in C++0x

    - by Austin Hyde
    C# has generic function types such as Action<T> or Func<T,U,V,...> With the advent of C++0x and the ability to have template typedef's and variadic template parameters, it seems this should be possible. The obvious solution to me would be this: template <typename T> using Action<T> = void (*)(T); however, this does not accommodate for functors or C++0x lambdas, and beyond that, does not compile with the error "expected unqualified-id before 'using'" My next attempt was to perhaps use boost::function: template <typename T> using Action<T> = boost::function<void (T)>; This doesn't compile either, for the same reason. My only other idea would be STL style template arguments: template <typename T, typename Action> void foo(T value, Action f) { f(value); } But this doesn't provide a strongly typed solution, and is only relevant inside the templated function. Now, I will be the first to admit that I am not the C++ wiz I prefer to think I am, so it's very possible there is an obvious solution I'm not seeing. Is it possible to have C# style generic function types in C++?

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  • Return nested alias for linq expression

    - by Schotime
    I have the following Linq Expression var tooDeep = shoppers .Where(x => x.Cart.CartSuppliers.First().Name == "Supplier1") .ToList(); I need to turn the name part into the following string. x.Cart.CartSuppliers.Name As part of this I turned the Expression into a string and then split on the . and removed the First() argument. However, when I get to CartSuppliers this returns a Suppliers[] array. Is there a way to get the single type from this. eg. I need to get a Supplier back. Thanks

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  • How do I write this as an expression?

    - by itchi
    I'm trying to rewrite a linq to entities query to an expression. My model is a School can have many Persons where Persons are inherited out to teachers, students, etc. The following query works for me: IQueryable<DAL.TEACHER> teacher = from p in School select p.PERSON as ESBDAL.TEACHER; How would I write this as a query expression? I thought something like: IQueryable<DAL.TEACHER> teacher = School.Select(x=>x.PERSON) as IQueryable<DAL.TEACHER>; ...but it does not. Am I misunderstanding the .Select()?

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  • LINQ: Dot Notation vs Query Expression

    - by Martín Marconcini
    I am beginning to use LINQ in general (so far toXML and toSQL). I've seen that sometimes there are two or more ways to achieve the same results. Take this simple example, as far as I understand both return exactly the same thing: SomeDataContext dc = new SomeDataContext(); var queue = from q in dc.SomeTable where q.SomeDate <= DateTime.Now && q.Locked != true orderby (q.Priority, q.TimeCreated) select q; var queue2 = dc.SomeTable .Where( q => q.SomeDate <= DateTime.Now && q.Locked != true ) .OrderBy(q => q.Priority) .ThenBy(q => q.TimeCreated); Besides any mistake I may have made in the syntax or a missing parameter or difference, the idea is that there are two ways to express the same thing; I understand that the first method has some limitations and that the "dot notation" is more complete, but besides that, are there any other advantages?

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  • Lamda functions in php

    - by Oden
    Hey, Im really interested in the way of using lamda functions. Does it make sense to use them in a high-level programming language? If yes, why? Is this really just a function embedded in a function, (Like this) or is there more behind?

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  • Why doesn't this (translated) VB.NET code work?

    - by ropstah
    I had a piece of C# code converted, but the translated code isn't valid... Can somebody help out? C# <table> <% Html.Repeater<Hobby>("Hobbies", "row", "row-alt", (hobby, css) => { %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% }); %> </table> VB <% Html.Repeater(of Jrc3.BLL.Product)(Model.ProductCollectionByPrcAutoKey, "row", "row-alt", Function(product, css) Do %> <tr class="<%= css %>"> <td><%= hobby.Title%></td> </tr> <% End Function)%>

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  • Use LINQ and lambdas to put string in proper case

    - by Tobias Funke
    I have this function called ProperCase that takes a string, then converts the first letter in each word to uppercase. So ProperCase("john smith") will return "John Smith". Here is the code: public string ProperCase(string input) { var retVal = string.Empty; var words = input.Split(' '); foreach (var word in words) { if (word.Length == 1) { retVal += word.ToUpper(); } else if (word.Length > 1) { retVal += word.Substring(0, 1).ToUpper() + word.Substring(1).ToLower(); } retVal += ' '; } if (retVal.Length > 0) { retVal = retVal.Substring(0, retVal.Length - 1); } return retVal; } This code workds perfectly, but I'm pretty sure I can do it more elegantly with LINQ and lambdas. Can some please show me how?

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  • Currying a function n times in Scheme

    - by user1724421
    I'm having trouble figuring out a way to curry a function a specified number of times. That is, I give the function a natural number n and a function fun, and it curries the function n times. For example: (curry n fun) Is the function and a possible application would be: (((((curry 4 +) 1) 2) 3) 4) Which would produce 10. I'm really not sure how to implement it properly. Could someone please give me a hand? Thanks :)

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  • Role of Combinators in Concatenative/Tacit Programming Languages.

    - by Bubba88
    Hi! I have a question about what exact role do higher-order compinators (or function producers) hold in concatenative/tacit programming. Additionally I would like to ask if there is another way to implement concatenative programming language rather than directly manipulating the stack. This might look like a newbie question, so if you feel like it, you can freely direct me to external source.

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  • Access the value of a member expression

    - by Schotime
    If i have a product. var p = new Product { Price = 30 }; and i have the following linq query. var q = repo.Products().Where(x=>x.Price == p.Price).ToList() In an IQueryable provider, I get a MemberExpression back for the p.Price which contains a Constant Expression, however I can't seem to get the value "30" back from it. Cheers.

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  • Fun with Lambdas

    - by Roman A. Taycher
    Not having them used them all that much I'm not quite sure all that lambdas/blocks can be used for (other than map/collect/do/lightweight local function syntax). If some people could post some interesting but somewhat understandable examples (with explanation). preferred languages for examples: python, smalltalk, haskell

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  • Return an empty collection when Linq where returns nothing

    - by ahsteele
    I am using the below statement with the intent of getting all of the machine objects from the MachineList collection (type IEnumerable) that have a MachineStatus of i. The MachineList collection will not always contain machines with a status of i. At times when no machines have a MachineStatus of i I'd like to return an empty collection. My call to ActiveMachines (which is used first) works but InactiveMachines does not. public IEnumerable<Machine> ActiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "a"); } } public IEnumerable<Machine> InactiveMachines { get { return Customer.MachineList .Where(m => m.MachineStatus == "i"); } } Edit Upon further examination it appears that any enumeration of MachineList will cause subsequent enumerations of MachineList to throw an exeception: Object reference not set to an instance of an object. Therefore, it doesn't matter if a call is made to ActiveMachines or InactiveMachines as its an issue with the MachineList collection. This is especially troubling because I can break calls to MachineList simply by enumerating it in a Watch before it is called in code. At its lowest level MachineList implements NHibernate.IQuery being returned as an IEnumerable. What's causing MachineList to lose its contents after an initial enumeration?

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  • LINQ: How to Use RemoveAll without using For loop with Array

    - by CrimsonX
    I currently have a log object I'd like to remove objects from, based on a LINQ query. I would like to remove all records in the log if the sum of the versions within a program are greater than 60. Currently I'm pretty confident that this'll work, but it seems kludgy: for (int index = 0; index < 4; index++) { Log.RemoveAll(log => (log.Program[index].Version[0].Value + log.Program[index].Version[1].Value + log.Program[index].Version[2].Value ) > 60); } The Program is an array of 4 values and version has an array of 3 values. Is there a more simple way to do this RemoveAll in LINQ without using the for loop? Thanks for any help in advance!

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  • Dynamic expression tree how to

    - by Savvas Sopiadis
    Hello everybody! Implemented a generic repository with several Methods. One of those is this: public IEnumerable<T> Find(Expression<Func<T, bool>> where) { return _objectSet.Where(where); } Given to be it is easy to call this like this: Expression<Func<Culture, bool>> whereClause = c => c.CultureId > 4 ; return cultureRepository.Find(whereClause).AsQueryable(); But now i see (realize) that this kind of quering is "limiting only to one criteria". What i would like to do is this: in the above example c is of type Culture. Culture has several properties like CultureId, Name, Displayname,... How would i express the following: CultureId 4 and Name.contains('de') and in another execution Name.contains('us') and Displayname.contains('ca') and .... Those queries should be created dynamically. I had a look in Expression trees (as i thought this to be a solution to my problem - btw i never used them before) but i cannot find anything which points to my requirement. How can this be costructed? Thanks in advance

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  • What is the cleanest way to use anonymous functions?

    - by Fletcher Moore
    I've started to use Javascript a lot more, and as a result I am writing things complex enough that organization is becoming a concern. However, this question applies to any language that allows you to nest functions. Essentially, when should you use an anonymous function over a named global or inner function? At first I thought it was the coolest feature ever, but I think I am going overboard. Here's an example I wrote recently, ommiting all the variable delcarations and conditionals so that you can see the structure. function printStream() { return fold(function (elem, acc) { ... var comments = (function () { return fold(function (comment, out) { ... return out + ...; }, '', elem.comments); return acc + ... + comments; }, '', data.stream); } I realized though (I think) there's some kind of beauty in being so compact, it is probably isn't a good idea to do this in the same way you wouldn't want a ton of code in a double for loop.

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  • Inline HTML Syntax for Helpers in ASP.NET MVC

    - by kouPhax
    I have a class that extends the HtmlHelper in MVC and allows me to use the builder pattern to construct special output e.g. <%= Html.FieldBuilder<MyModel>(builder => { builder.Field(model => model.PropertyOne); builder.Field(model => model.PropertyTwo); builder.Field(model => model.PropertyThree); }) %> Which outputs some application specific HTML, lets just say, <ul> <li>PropertyOne: 12</li> <li>PropertyTwo: Test</li> <li>PropertyThree: true</li> </ul> What I would like to do, however, is add a new builder methid for defining some inline HTML without having to store is as a string. E.g. I'd like to do this. <% Html.FieldBuilder<MyModel>(builder => { builder.Field(model => model.PropertyOne); builder.Field(model => model.PropertyTwo); builder.ActionField(model => %> Generated: <%=DateTime.Now.ToShortDate()%> (<a href="#">Refresh</a>) <%); }).Render(); %> and generate this <ul> <li>PropertyOne: 12</li> <li>PropertyTwo: Test</li> <li>Generated: 29/12/2008 <a href="#">Refresh</a></li> </ul> Essentially an ActionExpression that accepts a block of HTML. However to do this it seems I need to execute the expression but point the execution of the block to my own StringWriter and I am not sure how to do this. Can anyone advise?

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  • Coolest C# LINQ/Lambdas trick you've ever pulled?

    - by chakrit
    Saw a post about hidden features in C# but not a lot of people have written linq/lambdas example so... I wonder... What's the coolest (as in the most elegant) use of the C# LINQ and/or Lambdas/anonymous delegates you have ever saw/written? Bonus if it has went into production too!

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  • How does the proc in the caches_action if clause get execute

    - by Sid
    I have a newbie kind of question which I cant get my head around. How does the Proc in the if condition of the caches_action get executed for the caches_action method. for example caches_action :show, :if=Proc.new{|x| something} what i dont get its how does this get called. I know i can execute a proc defined as proc= Proc.new by proc.call so i dont understand how this gets called. Second how do I pass conditions like if logged_in? I'd appreciate any help on this

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  • Is there something like LINQ for Java?

    - by Kb
    Started to learn LINQ with C#. Especially LINQ to Objects and LINQ to XML. I really enjoy the power of LINQ. I learned that there is something called JLINQ a Jscript implementation. Also (as Catbert posted) Scala will have LINQ Do you know if LINQ or something similar will be a part of Java 7? Update: Interesting post from 2008 - http://stackoverflow.com/questions/346721/linq-for-java

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  • Lamda expression will not compile

    - by John Soer
    I am very confused I have this lamba expression tvPatientPrecriptionsEntities.Sort((p1, p2) => p1.MedicationStartDate.Value.CompareTo(p2.MedicationStartDate.Value)); Visual studio will not compile it and complains about syntax. I converted the lamba expression to an anonymous delegate as so tvPatientPrecriptionsEntities.Sort( delegate(PatientPrecriptionsEntity p1, PatientPrecriptionsEntity p2) { return p1.MedicationStartDate.Value.CompareTo(p2.MedicationStartDate.Value); } ); and it works fine. The project is uses the .net 3.5 framework and I have a reference to system.linq.

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  • How can I get the type I want?

    - by Danny Chen
    There are a lot of such classes in my project (very old and stable code, I can't do many changes to them, maybe slight changes are OK) public class MyEntity { public long ID { get; set; } public string Name { get; set; } public decimal Salary { get; set; } public static GetMyEntity ( long ID ) { MyEntity e = new MyEntity(); // load data from DB and bind to this instance return e; } } For some reasons, now I need to do this: Type t = Type.GetType("XXX"); // XXX is one of the above classes' name MethodInfo staticM= t.GetMethods(BindingFlags.Public | BindingFlags.Static).FirstOrDefault();// I'm sure I can get the correct one var o = staticM.Invoke(...); //returns a object, but I want the type above! If I pass "MyEntity" at beginning, I hope I can get o as MyEntity! Please NOTE that I know the "name of the class" only. MyEntity e = staticM.Invoke(...) as MyEntity; can't be used here.

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  • How to get XML into a Dictionary with an Expression?

    - by DaveDev
    I have the following XML: <PerformancePanel page="PerformancePanel.ascx" title=""> <FundGroup heading="Net Life Managed Funds"> <fund id="17" countryid="N0" index="24103723" /> <fund id="81" countryid="N0" index="24103723" /> <fund id="127" countryid="N0" index="24103722" /> <fund id="345" countryid="N0" index="24103723" /> <fund id="346" countryid="N0" index="24103723" /> </FundGroup> <FundGroup heading="Net Life Specialist Funds"> <fund id="110" countryid="N0" index="24103717" /> <fund id="150" countryid="N0" index="24103719" /> <fund id="119" countryid="N0" index="24103720" /> <fund id="115" countryid="N0" index="24103727" /> <fund id="141" countryid="N0" index="24103711" /> <fund id="137" countryid="N0" /> <fund id="146" countryid="N0" /> <fund id="133" countryid="N0" /> <fund id="90" countryid="N0" /> <fund id="104" countryid="N0" /> <fund id="96" countryid="N0" /> </FundGroup> </PerformancePanel> I can get the data into an anonymous object as follows: var offlineFactsheet = new { PerformancePanels = (from panel in doc.Elements("PerformancePanel") select new PerformancePanel { PerformanceFunds = (from fg in panel.Elements("FundGroup") select new { Heading = (fg.Attribute("heading") == null) ? "" : (string)fg.Attribute("heading"), Funds = (from fund in fg.Elements("fund") select new Fund { FundId = (int)fund.Attribute("id"), CountryId = (string)fund.Attribute("countryid"), FundIndex = (fund.Attribute("index") == null) ? null : new Index { Id = (int)fund.Attribute("index") }, FundNameAppend = (fund.Attribute("append") == null) ? "" : (string)fund.Attribute("append") }).ToList() }).ToDictionary(xx => xx.Heading, xx => xx.Funds)}; I'm trying to change my code such that I can assign the dictionary directly to a property of the class I'm working in, as described in this question. I'd like to have a Dictionary() where each header text is the key to the list of funds under it. I'm having difficulty applying the example in the linked question because that only returns a string, and this needs to return the dictionary. This is the point that I got to before it occurred to me that I'm lost!!!: this.PerformancePanels = doc.Elements("PerformancePanel").Select(e => { var control = (PerformancePanel)LoadControl(this.OfflineFactsheetPath + (string)e.Attribute("page")); control.PerformanceFunds = e.Elements("FundGroup").Select(f => { List<Fund> funds = (from fund in e.Elements("fund") select new Fund { FundId = (int)fund.Attribute("id"), CountryId = (string)fund.Attribute("countryid"), FundIndex = (fund.Attribute("index") == null) ? null : new Index { Id = (int)fund.Attribute("index") }, FundNameAppend = (fund.Attribute("append") == null) ? "" : (string)fund.Attribute("append") }).ToList(); string heading = (e.Attribute("heading") == null) ? "" : (string)e.Attribute("heading"); }).ToDictionary(xx => heading, xx => Funds); return control; }).ToList(); Could someone point me in the right direction please? I'm not even sure if 'Expression' is the right terminology. Could someone fill me in on that too? Thanks.

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  • AutoMapper and Linq expression.

    - by Raffaeu
    I am exposing the Dto generated from AutoMapper to my WCF services. I would like to offer something like that from WCF: IList GetPersonByQuery(Expression predicate); Unfortunately I need back an expression tree of Person as my DAL doesn't know the DTO. I am trying this wihtout success: var func = new Func<Person, bool>(x => x.FirstName.Contains("John")); var funcDto = Mapper.Map<Func<Person, bool>, Func<PersonDto, bool>>(func); Console.WriteLine(func.ToString()); Console.WriteLine(funcDto.ToString()); THe error that I get is: ----> System.ArgumentException : Type 'System.Func`2[TestAutoMapper.PersonDto,System.Boolean]' does not have a default constructor Do you have any suggestions?

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  • OrderBy Linq.Expression as parameter = (Of Func(Of T,IComparable)) to perform LinqToEntity is not working

    - by NicoJuicy
    I'd like to get this working: Call: (Count & Page are used for pagination, so Count = 20 and Page = 1 for example, for the first 20 values). Sorting should be by name LeverancierService.GetLeveranciers(Function(el) el.Name, Count, Page) Equivalent in c#: LeverancierService.GetLeveranciers(el= el.Name, Count, Page) Method that gives an error (parameters shown above): Public Overridable Function GetAllPaged(orderby As Expression(Of Func(Of T, IComparable)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Already tried changing it to this, but it gives the same error: Public Overridable Function GetAllPaged(Of TOrderBy)(orderby As Expression(Of Func(Of T, TOrderBy)), ByVal Count As Integer, ByVal Page As Integer) As IEnumerable(Of T) Return dbset.OrderBy(orderby).Skip((Page - 1) * Count).Take(Count).ToList() End Function Error: Unable to cast the type 'System.String' to type 'System.IComparable'. LINQ to Entities only supports casting Entity Data Model primitive types. Any idea how to do this? Extra info: I'm in a DDD-layered application, so the parameter should stay the same as the called method is an overridden interface (eg. if i change this, i have to do this for 200 times or so, because it's in VB.Net and not in C# (= 1 change) ) I know there is a way to change the expression to a string and then use DLinq (= Dynamic Linq), but that's not how it should be.

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