lambda

"Type arguments cannot be inferred" error when using Html.TextboxFor with a ViewModel in an ASP.NET MVC 2 View

I'm writing an ASP.NET MVC 2 site where I have defined a custom ViewModel that I'm trying to use in a View. Unfortunately, I'm running into an error when using the ViewModel through a strongly-typed lambda expression. My Code Here's my ViewModel: [CompareProperties(ComparisonProperty1="EmailAddress", ComparisonProperty2="Confirm...

Lambda expressions automated packing

public void aMethod<T>(Expression<Func<T, object>> lambda) { ...... } aMethod<User>(x=> x.UserId) User is my custom class, members of his UserId int type... I want the lambda expression x => x.UserId But in the way, I get is x => Convert (x.UserId) Therefore, the following operations can not, I need to ensure that my expression ...

How to translate lambda expressions to the TSQL statement

e.g. x => x.UserId > 5 && x.Name.StartWith("S") && x.Name.EndWith("D") && x.Name.Contains("x") to it.UserId > 5 And it.Name like 'S%' And it.Name like '%D' And it.Name like '%x%' ...

How do I take a lambda expression as a parameter that returns a method?

I want to be able to do this: var test = SomeMethod(s => s.SomeMethod); I can make it work with properties by making the method signature look like this: SomeMethod<TProperty>(Expression<Func<T, TProperty>> expression) How can I make it work with methods? I know this is simple, I'm just missing something small. ...

Why is param in this lambda expression?

The MSDN magazine article by Josh Smith on MVVM contains a lambda expression I don't completely understand. What is the purpose of param in this code? _saveCommand = new RelayCommand(param => this.Save(), param => this.CanSave ); Translated to my preferred language VB it's: Dim saveAction as New Action(Of Object)(Addr...

Threading Method Question

I'm using the following method to show a modeless Message Box. public void ShowMessageBox(string Message) { var thread = new Thread( () => { MessageBox.Show(Message); }); thread.Start(); } The "() => {...}" is something I've never seen before. What is the name for this code pattern? Also, thread.Start start...

C++0x lambda, how can I pass as a parameter?

Please look at the following C++0x lambda related code: typedef uint64_t (*WEIGHT_FUNC)(void* param); typedef std::map<std::string, WEIGHT_FUNC> CallbackTable; CallbackTable table; table["rand_weight"] = [](void* param) -> uint64_t { return (rand() % 100 + 1); }; I got an error (in Visual Studio 2010) that the lambda couldn't be co...

Strange "Could not deduce template argument for 'T'" error

The error is in this code: //myutil.h template <class T, class predicate> T ConditionalInput(LPSTR inputMessage, LPSTR errorMessage, predicate condition); //myutil.cpp template <class T, class Pred> T ConditionalInput(LPSTR inputMessage, LPSTR errorMessage, Pred condition) { T input cout<< inputMessage; cin>...

How can I use PHP 5.3 Closures like We use Blocks in Ruby

How can I use PHP 5.3 Closures like We use Blocks in Ruby. I never used 'for' Loop in Ruby due to using Blocks with 'each' 'find_all' 'inject' Methods. How can I use PHP 5.3 Closures like Ruby Blocks and say bye-bye to 'for' Loops :) Like Between { and } is a Closure(or Block or Anonymous Function) fruit = %w[apple banana orange] frui...

Using a lambda expression to avoid using a "magic string" to specify a property

I am writing a service to take a collection of objects of a particular type and output its primitive, string, and DateTime types to a string in CSV Format. I have both of the below statements working. I find the the lambda based version to be much cleaner. Magic String Version string csv = new ToCsvService<DateTime>(objs) .Exclude(...

Creating an expression tree that calls a method

Is it possible to create an expression tree that directly calls a method? For example, consider the following method: public static int MyFunc(int a, int b) { return a + b; } I would like to create an expression tree that calls MyFunc with parameters a=1 and b=2. One way to accomplish this is with reflection: var c1 = Expression....

Lambda Help Grouping and Summing in C#, need a Func<IGrouping<int, anonymous type, int> or Expression<Func<IGrouping<int, anonymous type>, decimal>>

I'm having a bit of trouble doing an inline .GroupBy() and .Sum() action. I have a subset of data obtained via a let so it's return type is already anonymous. Hopefully there's enough code in this sample to show what I'm trying to achieve... from r in Repo.R join f in Repo.F on f.ID equals r.FFK let totalB = Repo.B .Join( ...

How does one create a .NET Expression with NodeType of ExpressionType.Index?

I'm writing code that evaluates .NET Expression trees. I'm trying to create a C# 4 test to exercise my handling of an ExpressionType.Index, but I can't figure out how to create that type of expression through a LambdaExpression. No matter what I try, the expression comes out as an ExpressionType.Call or ExpressionType.ArrayIndex. For ...

Use (certain) lambda expressions when targeting .NET 2.0?

Hi, ReSharper suggests we change: System.Net.ServicePointManager.ServerCertificateValidationCallback += delegate(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors) { return true; }; Into: System.Net.ServicePointManager.ServerCertificateValidationCallback += (sender, cert...

How Iterate from list of Anonymous Types?

Hi, i have this linq to entities query: c.CreateQuery<T_Hotels>("T_Hotels").Where(item => item.Id > 0).GroupBy(item => new { item.Location, item.Name }).Select(group => new { group.Key, Total = group.Sum(item => item.Id) }) I want to implement everything in a method of a class Helper, how declare the expressions of GroupBy and Select...

Selecting distinct objects from collection of objects using lambda expressions

We have a project using Fluent NHibernate. There is an object called BluePart with a property of Oem of type Oem. public class BluePart : DomainEntity { ... public virtual Oem Oem { get; set; } } The Oem object has several properties including OemCode and OemDescription. public class Oem : DomainEntity { ... public vi...

Invoke an Expression in a Select statement - LINQ to Entity Framework

I'm trying to use an already existing Expression building class that I made when trying to do a select clause, but I'm not sure how to attach the expression to the expression tree for the Select, I tried doing the following: var catalogs = matchingCatalogs.Select(c => new { c.CatalogID, ...

C++0x Lambda to function pointer in VS 2010

I am trying to use a lambda to pass in place of a function pointer but VS2010 can't seem to convert it. I have tried using std::function like this and it crashes and I have no idea if I am doing this right! #include <windows.h> #include <conio.h> #include <functional> #include <iostream> #include <concrt.h> void main() { std::f...

How does NHibernate 3 solve the QueryOver<> syntax?

I'm curious on how the NHibernate team has solved the QueryOver syntax, so that it works with intellisense and validation at compile time? According to http://nhforge.org/blogs/nhibernate/archive/2009/12/17/queryover-in-nh-3-0.aspx they make use of extension methods and lambda expressions, but I've tried looking through the source but i...

Use Linq and lambda to flatten a list

Hi there I have a class. public class MedicalRequest { private int id private IList<MedicalDays> Days private string MedicalUser ... } and another public class MedicalDays { private int id; private DateTime? day private MedicalRequest request ... } I have the MedicalUser so I'm able to select an I...