Search Results

Search found 968 results on 39 pages for 'lambda'.

Page 12/39 | < Previous Page | 8 9 10 11 12 13 14 15 16 17 18 19  | Next Page >

• Executing a modified expression

  - by Sam

  I found this brief demo: http://msdn.microsoft.com/en-us/library/bb546136.aspx Which discusses modifying an expression. However the code starts with a Expression<Func<string, bool>> and ends up with a Expression so it's not complete. How do I take that expression and make it typed as Expression<Func<string,bool>> again? All the examples I have have found on executing an expression all involve dynamically created expressions which is not what this case has. Here the original expression is defined at compile time. And the code I want to write to do this won't know much about the expression, ideally as little as possible. I definately can't see how I would know what "Paramaters" to pass to Expression.LambdaExpression... In my particular case I want to search for any references to a particular propery of type A and swap them out with a reference to a property of type B then pass the expression to a call to IEnumerable.Where. ie. p=>p.Name == "Sam" where P is Foo1 becomes p=>p.FirstName == "Sam" where p is Foo2

  Read the article

• How can I combine several Expressions into a fast method?

  - by chillitom

  Suppose I have the following expressions: Expression<Action<T, StringBuilder>> expr1 = (t, sb) => sb.Append(t.Name); Expression<Action<T, StringBuilder>> expr2 = (t, sb) => sb.Append(", "); Expression<Action<T, StringBuilder>> expr3 = (t, sb) => sb.Append(t.Description); I'd like to be able to compile these into a method/delegate equivalent to the following: void Method(T t, StringBuilder sb) { sb.Append(t.Name); sb.Append(", "); sb.Append(t.Description); } What is the best way to approach this? I'd like it to perform well, ideally with performance equivalent to the above method. UPDATE So, whilst it appears that there is no way to do this directly in C#3 is there a way to convert an expression to IL so that I can use it with System.Reflection.Emit?

  Read the article

• Linq to SQL DynamicInvoke(System.Object[])' has no supported translation to SQL.

  - by ewwwyn

  I have a class, Users. Users has a UserId property. I have a method that looks something like this: static IQueryable<User> FilterById(this IQueryable<User> p, Func<int, bool> sel) { return p.Where(m => sel(m)); } Inevitably, when I call the function: var users = Users.FilterById(m => m > 10); I get the following exception: Method 'System.Object DynamicInvoke(System.Object[])' has no supported translation to SQL. Is there any solution to this problem? How far down the rabbit hole of Expression.KillMeAndMyFamily() might I have to go? To clarify why I'm doing this: I'm using T4 templates to autogenerate a simple repository and a system of pipes. Within the pipes, instead of writing: new UserPipe().Where(m => m.UserId > 10 && m.UserName.Contains("oo") && m.LastName == "Wee"); I'd like to generate something like: new UserPipe() .UserId(m => m > 10) .UserName(m => m.Contains("oo")) .LastName("Wee");

  Read the article

• Strongly typed API for ASP.NET MVC 2 async actions

  - by Alexey Zakharov

  Hi guys, Have anybody tried to create strongly typed API for ASP.NET MVC 2 async actions? Best regards, Alexey Zakharov

  Read the article

• C++0x and the Lack of Polymorphic Lambdas - Why?

  - by Dominar

  I've been reviewing the draft version of the upcoming C++0x standard. Specifically the section on lambdas, and am confused as to the reasoning for not introducing polymorphic lambdas. I had hoped we could use code such as the following: template<typename Container> void foo(Container c) { for_each(c.begin(),c.end(),[](T& t) { ++t; }); } What were the reasons: Was it the committee ran out of time? That polymorphic lambdas are too hard to implement? Or perhaps that they are seen as not being needed by the PTB?

  Read the article

• Dictionary<string,string> to Dictionary<Control,object> using IEnumerable<T>.Select()

  - by abatishchev

  I have a System.Collections.Generic.Dictionary<string, string> containing control ID and appropriate data column to data bind: var dic = new Dictionary<string, string> { { "Label1", "FooCount" }, { "Label2", "BarCount" } }; I use it that way: var row = ((DataRowView)FormView1.DataItem).Row; Dictionary<Control, object> newOne = dic.ToDictionary( k => FormView1.FindControl(k.Key)), k => row[k.Value]); So I'm using IEnumerable<T>.ToDictionary(Func<T>, Func<T>). Is it possbile to do the same using IEnumerable<T>.Select(Func<T>) ?

  Read the article

• Javascript: Calling a function written in an anonymous function from String with the function's name

  - by Kai barry yuzanic

  Hello. I've started using jQuery and am wondering how to call functions in an anonymous function dynamically from String. Let's say for instance, I have the following functions: function foo() { // Being in the global namespace, // this function can be called with window['foo']() alert("foo"); } jQuery(document).ready(function(){ function bar() { // How can this function be called // by using a String of the function's name 'bar'?? alert("bar"); } // I want to call the function bar here from String with the name 'bar' } I've been trying to figure out what could be the counterpart of 'window', which can call functions from the global namespace such as window["foo"]. In the small example above, how I can call the function bar from a String "bar"? Thank you for your help.

  Read the article

• PHP sandbox/sanitize code passed to create_function

  - by kpowerinfinity

  Hello, I am using create_function to run some user-code at server end. I am looking for any of these two: Is there a way to sanitize the code passed to it to prevent something harmful from executing? Alternately, is there a way to specify this code to be run in a sandboxed environment so that the user can't play around with anything else. Thanks!

  Read the article

• Problem in populating a dictionary using Enumerable.Range()

  - by Newbie

  If I do for (int i = 0; i < appSettings.Count; i++) { string key = appSettings.Keys[i]; euFileDictionary.Add(key, appSettings[i]); } It is working fine. When I am trying the same thing using Enumerable.Range(0, appSettings.Count).Select(i => { string Key = appSettings.Keys[i]; string Value = appSettings[i]; euFileDictionary.Add(Key, Value); }).ToDictionary<string,string>(); I am getting a compile time error The type arguments for method 'System.Linq.Enumerable.Select(System.Collections.Generic.IEnumerable, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly. Any idea? Using C#3.0 Thanks

  Read the article

• Undefined symbols for C++0x lambdas?

  - by Austin Hyde

  I was just poking around into some new stuff in C++0x, when I hit a stumbling block: #include <list> #include <cstdio> using namespace std; template <typename T,typename F> void ForEach (list<T> l, F f) { for (typename list<T>::iterator it=l.begin();it!=l.end();++it) f(*it); } int main() { int arr[] = {1,2,3,4,5,6}; list<int> l (arr,arr+6); ForEach(l,[](int x){printf("%d\n",x);}); } does not compile. I get a load of undefined symbol errors. Here's make's output: i386-apple-darwin9-gcc-4.5.0 -std=c++0x -I/usr/local/include -o func main.cpp Undefined symbols: "___cxa_rethrow", referenced from: std::_List_node<int>* std::list<int, std::allocator<int> >::_M_create_node<int const&>(int const&&&) in ccPxxPwU.o "operator new(unsigned long)", referenced from: __gnu_cxx::new_allocator<std::_List_node<int> >::allocate(unsigned long, void const*) in ccPxxPwU.o "___gxx_personality_v0", referenced from: ___gxx_personality_v0$non_lazy_ptr in ccPxxPwU.o "___cxa_begin_catch", referenced from: std::_List_node<int>* std::list<int, std::allocator<int> >::_M_create_node<int const&>(int const&&&) in ccPxxPwU.o "operator delete(void*)", referenced from: __gnu_cxx::new_allocator<std::_List_node<int> >::deallocate(std::_List_node<int>*, unsigned long) in ccPxxPwU.o "___cxa_end_catch", referenced from: std::_List_node<int>* std::list<int, std::allocator<int> >::_M_create_node<int const&>(int const&&&) in ccPxxPwU.o "std::__throw_bad_alloc()", referenced from: __gnu_cxx::new_allocator<std::_List_node<int> >::allocate(unsigned long, void const*) in ccPxxPwU.o "std::_List_node_base::_M_hook(std::_List_node_base*)", referenced from: void std::list<int, std::allocator<int> >::_M_insert<int const&>(std::_List_iterator<int>, int const&&&) in ccPxxPwU.o ld: symbol(s) not found collect2: ld returned 1 exit status make: *** [func] Error 1 Why is this not working?

  Read the article

• How can I combine sequential expression trees into a fast method?

  - by chillitom

  Suppose I have the following expressions: Expression<Action<T, StringBuilder>> expr1 = (t, sb) => sb.Append(t.Name); Expression<Action<T, StringBuilder>> expr2 = (t, sb) => sb.Append(", "); Expression<Action<T, StringBuilder>> expr3 = (t, sb) => sb.Append(t.Description); I'd like to be able to compile these into a method/delegate equivalent to the following: void Method(T t, StringBuilder sb) { sb.Append(t.Name); sb.Append(", "); sb.Append(t.Description); } What is the best way to approach this? I'd like it to perform well, ideally with performance equivalent to the above method.

  Read the article

• parsing expression trees with booleans

  - by Schotime

  I am trying to parse an expression tree for a linq provider and running into a little snag with booleans. I can parse this no problems. var p = products.Where(x=>x.IsAvailable == true).ToList(); however when its written like this? var p = products.Where(x=>x.IsAvailable).ToList(); i only get a MemberAccess to look at and i can't see how i deduce that it is true or false (!x.IsAvailable). Any help would be great. Thanks.

  Read the article

• How do I get a value of a reference type in an Expression?

  - by Jon Kruger

  I have this method: public void DoSomething<T>(Expression<Func<T, object>> method) { } If this method is called like this: DoSomething(c => c.SomeMethod(new TestObject())); ... how do I get the value of the parameter that was passed into SomeMethod()? If the parameter is a value type, this works: var methodCall = (MethodCallExpression)method.Body; var parameterValue = ((ConstantExpression)methodCall.Arguments[0]).Value; However, when I pass in a reference type, methodCall.Arguments[0] is a MemberExpression, and I can't seem to figure out how to write code to get the value out of it.

  Read the article

• 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

  Read the article

• 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++?

  Read the article

• 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?

  Read the article

• 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()?

  Read the article

• 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?

  Read the article

• Linq and Lamba Expressions - while walking a selected list perform an action

  - by Prescott

  Hey, I'm very new to linq and lamba expressions. I'm trying to walk a collection, and when I find an item that meets some criteria I'd like to add that to another separate collection. My linq to walk the collection looks like this (this works fine): From i as MyCustomItem In MyCustomItemCollection Where i.Type = "SomeType" Select i I need each of the select items to then be added to a ListItemCollection, I know I can assign that linq query to a variable, and then do a for each loop adding a new ListItem to the collection, but I'm trying o find a way to add each item to the new ListItemcollection while walking, not a second loop. Thanks ~P

  Read the article

• 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)%>

  Read the article

• 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?

  Read the article

• Can a class inherit from LambdaExpression in .NET? Or is this not recommended?

  - by d.

  Consider the following code (C# 4.0): public class Foo : LambdaExpression { } This throws the following design-time error: Foo does not implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) There's absolutely no problem with public class Foo : Expression { } but, out of curiosity and for the sake of learning, I've searched in Google System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) and guess what: zero results returned (when was the last time you saw that?). Needless to say, I haven't found any documentation on this method anywhere else. As I said, one can easily inherit from Expression; on the other hand LambdaExpression, while not marked as sealed (Expression<TDelegate> inherits from it), seems to be designed to prevent inheriting from it. Is this actually the case? Does anyone out there know what this method is about? EDIT (1): More info based on the first answers - If you try to implement Accept, the editor (C# 2010 Express) automatically gives you the following stub: protected override Expression Accept(System.Linq.Expressions.ExpressionVisitor visitor) { return base.Accept(visitor); } But you still get the same error. If you try to use a parameter of type StackSpiller directly, the compiler throws a different error: System.Linq.Expressions.Compiler.StackSpiller is inaccessible due to its protection level. EDIT (2): Based on other answers, inheriting from LambdaExpression is not possible so the question as to whether or not it is recommended becomes irrelevant. I wonder if, in cases like this, the error message should be Foo cannot implement inherited abstract member System.Linq.Expressions.LambdaExpression.Accept(System.Linq.Expressions.Compiler.StackSpiller) because [reasons go here]; the current error message (as some answers prove) seems to tell me that all I need to do is implement Accept (which I can't do).

  Read the article

• 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 :)

  Read the article

• 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.

  Read the article

• 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.

  Read the article

< Previous Page | 8 9 10 11 12 13 14 15 16 17 18 19  | Next Page >