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  • To Reference A Generic Method With A Lambda Expression

    - by SDReyes
    It is possible to reference a generic method using a Lambda Expression Object? For example, having: TheObject: public abstract class LambdaExpression : Expression TheMethod (an extension method of LINQ): public static TSource Last<TSource>( this IEnumerable<TSource> source ) I'm trying to create an instance of TheObject, that references to TheMethod. How do you do such thing?

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  • Rewriting a statement using LAMBDA(C#)

    - by Thinking
    Is it possible to write the folowing using lambda(C#) private static void GetRecordList(List<CustomerInfo> lstCustinfo) { for (int i = 1; i <= 5; i++) { if (i % 2 == 0) lstCustinfo.Add(new CustomerInfo { CountryCode = "USA", CustomerAddress = "US Address" + i.ToString(), CustomerName = "US Customer Name" + i.ToString(), ForeignAmount = i * 50 }); else lstCustinfo.Add(new CustomerInfo { CountryCode = "UK", CustomerAddress = "UK Address" + i.ToString(), CustomerName = "UK Customer Name" + i.ToString(), ForeignAmount = i * 80 }); } }

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  • Lambda Expressions and Memory Management

    - by Surya
    How do the Lambda Expressions / Closures in C++0x complicate the memory management in C++? Why do some people say that closures have no place in languages with manual memory management? Is there claim valid and if yes, what are the reasons behind it?

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  • Correct use of boost lambda

    - by Niels P.
    Consider the following piece of C++0x code: a_signal.connect([](int i) { if(boost::any_cast<std::string>(_buffer[i]) == "foo") { base_class<>* an_object = new derived_class(); an_object->a_method(_buffer[i]); }}); How would it correctly look in Boost Lambda (since this C++0x feature can't be used yet)?

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  • Lambda functions

    - by Oden
    Hey, I'm really interested in the way of using lambda 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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  • using lambda instead of let in scheme

    - by Radagaisus
    Hey, In SICP 1.2.1 there is a function that makes a rational number, as follow: (define (make-rat n d) (let ((g (gcd n d))) (cons (/ n g) (/ d g)))) I'm just curious how you can implement the same thing using lambda instead of let, without calling GCD twice. I couldn't figure it out myself.

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  • Lambda recursive PHP functions.

    - by Kendall Hopkins
    Is it possible to have a PHP function that is both recursive and anonymous (lambda). This is my attempt to get it to work, but it doesn't pass in the function name. $factorial = function( $n ) use ( $factorial ) { if( $n == 1 ) return 1; return $factorial( $n - 1 ) * $n; }; print $factorial( 5 ); I'm also aware that this is a bad way to implement factorial, it's just an example.

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  • Perfect Forwarding to async lambda

    - by Alexander Kondratskiy
    I have a function template, where I want to do perfect forwarding into a lambda that I run on another thread. Here is a minimal test case which you can directly compile: #include <thread> #include <future> #include <utility> #include <iostream> #include <vector> /** * Function template that does perfect forwarding to a lambda inside an * async call (or at least tries to). I want both instantiations of the * function to work (one for lvalue references T&, and rvalue reference T&&). * However, I cannot get the code to compile when calling it with an lvalue. * See main() below. */ template <typename T> std::string accessValueAsync(T&& obj) { std::future<std::string> fut = std::async(std::launch::async, [](T&& vec) mutable { return vec[0]; }, std::forward<T>(obj)); return fut.get(); } int main(int argc, char const *argv[]) { std::vector<std::string> lvalue{"Testing"}; // calling with what I assume is an lvalue reference does NOT compile std::cout << accessValueAsync(lvalue) << std::endl; // calling with rvalue reference compiles std::cout << accessValueAsync(std::move(lvalue)) << std::endl; // I want both to compile. return 0; } For the non-compiling case, here is the last line of the error message which is intelligible: main.cpp|13 col 29| note: no known conversion for argument 1 from ‘std::vector<std::basic_string<char> >’ to ‘std::vector<std::basic_string<char> >&’ I have a feeling it may have something to do with how T&& is deduced, but I can't pinpoint the exact point of failure and fix it. Any suggestions? Thank you! EDIT: I am using gcc 4.7.0 just in case this could be a compiler issue (probably not)

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  • check that int array contains !=0 value using lambda

    - by netmajor
    hey, I have two-dimension array List<List<int>> boardArray How can I enumerate throw this array to check that it contains other value than 0 ? I think about boardArray.Contains and ForEach ,cause it return bool value but I don't have too much experience with lambda expression :/ Please help :)

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  • C# Lambda Expression Speed

    - by Nathan
    I have not used many lambda expressions before and I ran into a case where I thought I could make slick use of one. I have a custom list of ~19,000 records and I need to find out if a record exists or not in the list so instead of writing a bunch of loops or using linq to go through the list I decided to try this: for (int i = MinX; i <= MaxX; ++i) { tempY = MinY; while (tempY <= MaxY) { bool exists = myList.Exists(item => item.XCoord == i && item.YCoord == tempY); ++tempY; } } Only problem is it take ~9 - 11 seconds to execute. Am I doing something wrong is this just a case of where I shouldn't be using an expression like this? Thanks.

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  • LINQ query and lambda expressions

    - by user329269
    I'm trying to write a LINQ query and am having problems. I'm not sure if lambda expressions are the answer or not but I think they may be. I have two combo boxes on my form: "State" and "Color". I want to select Widgets from my database based on the values of these two dropdowns. My widgets can be in one of the following states: Not Started, In Production, In Finishing, In Inventory, Sold. Widgets can have any color in the 'color' table in the database. The 'state' combobox has selections "Not Sold," "In Production/Finishing", "Not Started," "In Production," "In Finishing," "In Inventory," "Sold." (I hope these are self-explanatory.) The 'color' dropdown has "All Colors," and a separate item for each color in the database. How can I create a LINQ query to select the widgets I want from the database based on the dropdowns?

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  • Problem with nested lambda expressions.

    - by Lehto
    Hey I'm trying to do a nested lambda expression like to following: textLocalizationTable.Where( z => z.SpokenLanguage.Any( x => x.FromCulture == "en-GB") ).ToList(); but i get the error: Member access 'System.String FromCulture' of 'DomainModel.Entities.SpokenLanguage' not legal on type 'System.Data.Linq.EntitySet`1[DomainModel.Entities.SpokenLanguage]. TextLocalization has this relation to spokenlanguage: [Association(OtherKey = "LocalizationID", ThisKey = "LocalizationID", Storage = "_SpokenLanguage")] private EntitySet<SpokenLanguage> _SpokenLanguage = new EntitySet<SpokenLanguage>(); public EntitySet<SpokenLanguage> SpokenLanguage { set { _SpokenLanguage = value; } get { return _SpokenLanguage; } } Any idea what is wrong?

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  • .NET C# setting the value of a field defined by a lambda selector

    - by Frank Michael Kraft
    I have a generic class HierarchicalBusinessObject. In the constructor of the class I pass a lambda expression that defines a selector to a field of TModel. protected HierarchicalBusinessObject (Expression<Func<TModel,string>> parentSelector) A call would look like this, for example: public class WorkitemBusinessObject : HierarchicalBusinessObject<Workitem,WorkitemDataContext> { public WorkitemBusinessObject() : base(w => w.SuperWorkitem, w => w.TopLevel == true) { } } I am able to use the selector for read within the class. For example: sourceList.Select(_parentSelector.Compile()).Where(... Now I am asking myself how I could use the selector to set a value to the field. Something like selector.Body() .... Field...

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  • Lambda expressions and nullable types

    - by Mathew
    I have two samples of code. One works and returns the correct result, one throws a null reference exception. What's the difference? I know there's some magic happening with capturing variables for the lambda expression but I don't understand what's going on behind the scenes here. int? x = null; bool isXNull = !x.HasValue; // this works var result = from p in data.Program where (isXNull) select p; return result.Tolist(); // this doesn't var result2 = from p in data.Program where (!x.HasValue) select p; return result2.ToList();

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  • Using a linq or lambda expression in C# return a collection plus a single value

    - by ahsteele
    I'd like to return a collection plus a single value. Presently I am using a field to create a new list adding a value to the list and then returning the result. Is there a way to do this with a linq or lambda expression? private List<ChargeDetail> _chargeBreakdown = new List<ChargeDetail>(); public ChargeDetail PrimaryChargeDetail { get; set; } public List<ChargeDetail> ChargeBreakdown { get { List<ChargeDetail> result = new List<ChargeDetail>(_chargeBreakdown); result.Add(PrimaryChargeDetail); return result; } }

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  • Using Lambda Statements for Event Handlers

    - by lush
    I currently have a page which is declared as follows: public partial class MyPage : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { //snip MyButton.Click += (o, i) => { //snip } } } I've only recently moved to .NET 3.5 from 1.1, so I'm used to writing event handlers outside of the Page_Load. My question is; are there any performance drawbacks or pitfalls I should watch out for when using the lambda method for this? I prefer it, as it's certainly more concise, but I do not want to sacrifice performance to use it. Thanks.

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  • Wrap Sub as Function for use in Lambda

    - by Luhmann
    I have a problem with VB and Moq. I need to call a verify on a Sub. Like so: logger.Verify(Function(x) x.Log, Times.AtLeastOnce) And my logger looks like this: Public Interface ILogger Sub Log() End Interface But with VB this is not possible, because the Log method is a Sub, and thereby does not produce a value. I don't want to change the method to be a function. Whats the cleanest way of working around this limitation and is there any way to wrap the Sub as a Function like the below? logger.Verify(Function(x) ToFunc(AddressOf x.Log)) I have tried this, but i get: Lambda Parameter not in scope

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  • lambda+for_each+delete on STL containers

    - by rubenvb
    I'm trying to get a simple delete every pointer in my vector/list/... function written with an ultra cool lambda function. Mind you, I don't know c**p about those things :) template <typename T> void delete_clear(T const& cont) { for_each(T.begin(), T.end(), [](???){ ???->delete() } ); T.clear(); } I have no clue what to fill in for the ???'s. Any help is greatly appreciated!

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