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  • 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");

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  • 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>) ?

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  • 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?

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  • 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!

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  • C++ wrapper for posix and linux specific functions

    - by Libzajc
    Hi Do you know about any good library wrapping posix and linux functions and structures ( eg. sockets or file descriptors ) into C++ classes? For example I'm thinking about a base FileDescriptor class and some inheriting classes ( unix sockets etc ) with methods like write, read or even some syscalls ( sendfile, splice ) - all throwing exceptions instead of setting errno. Or some shared memory class etc. I can't seem to find anything like that and by now I consider writing it myself, as I often have to write a C++ app for linux and either use C functions ( painful error checking ), or wrap them myself every time.

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  • 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

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  • 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?

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  • 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.

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  • 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.

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  • 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.

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  • pointers to functions

    - by DevAno1
    I have two basic Cpp tasks, but still I have problems with them. First is to write functions mul1,div1,sub1,sum1, taking ints as arguments and returning ints. Then I need to create pointers ptrFun1 and ptrFun2 to functions mul1 and sum1, and print results of using them. Problem starts with defining those pointers. I thought I was doing it right, but devcpp gives me errors in compilation. #include <iostream> using namespace std; int mul1(int a,int b) { return a * b; } int div1(int a,int b) { return a / b; } int sum1(int a,int b) { return a + b; } int sub1(int a,int b) { return a - b; } int main() { int a=1; int b=5; cout << mul1(a,b) << endl; cout << div1(a,b) << endl; cout << sum1(a,b) << endl; cout << sub1(a,b) << endl; int *funPtr1(int, int); int *funPtr2(int, int); funPtr1 = sum1; funPtr2 = mul1; cout << funPtr1(a,b) << endl; cout << funPtr2(a,b) << endl; system("PAUSE"); return 0; } 38 assignment of function int* funPtr1(int, int)' 38 cannot convertint ()(int, int)' to `int*()(int, int)' in assignment Task 2 is to create array of pointers to those functions named tabFunPtr. How to do that ?

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  • 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

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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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  • 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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  • 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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  • 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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  • 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).

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  • Reducing Code Repetition: Calling functions with slightly different signatures

    - by Brian
    Suppose I have two functions which look like this: public static void myFunction1(int a, int b, int c, string d) { //dostuff someoneelsesfunction(c,d); //dostuff2 } public static void myFunction2(int a, int b, int c, Stream d) { //dostuff someoneelsesfunction(c,d); //dostuff2 } What would be a good way to avoid repeated dostuff? Ideas I've thought of, but don't like: I could make d an object and cast at runtype based on type, but this strikes me as not being ideal; it removes a type check which was previously happening at compile time. I could also write a private helper class that takes an object and write both signatures as public functions. I could replace dostuff and dostuff2 with delegates or function calls or something.

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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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