I know I must be missing something really obvious here. B.GetInstance().Call() generates the error: Lookup on object of indeterminate type based on information prior to this program point. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved. I'm using ...
if i do any isUpper "asBsd", i'll get True. here, the second element to any is a string. but, if i do this: any ("1" `isInfixOf`) ["qas","123","=-0"] the second element to any is a list of strings. how and why this difference between those 2 functions? another example. if i write filter isUpper "asdVdf" , i'll get "V". here, the se...
I've got a function which takes an input of type ('a * (float * 'b * float)) list Where I'd obviously like to avoid having to explicitly include the type. The problem is that I convert the second float to decimal, using the decimal function. let v2 (_,(_,_,v)) = decimal v So type inference defaults to seeing this: ('a * (float * ...
I would like make an extension method for the generic class A which takes yet another generictype (in this example TC), but i guess that aint possible? class Program { static void Main(string[] args) { var a = new A<B, B>(); a.DoIt<B>(); } } static class Ext { public static A<TA, TB> DoIt<TA, TB, TC>(th...
Is it a common pattern/idiom to use free functions as pseudo-constructors to avoid having to explicitly specify template parameters? For example, everyone knows about std::make_pair, which uses its parameters to deduce the pair types: template <class A, class B> std::pair<A, B> make_pair(A a, B b) { return std::pair<A, B>(a, b); } /...
I have the following simple Java code: package testj; import java.util.*; public class Query<T> { private static List<Object> l = Arrays.<Object>asList(1, "Hello", 3.0); private final Class<? extends T> clazz; public static Query<Object> newQuery() { return new Query<Object>(Object.class); } public Query(Class<? ext...
So I'm trying to learn more about lambda expressions. I read this question on stackoverflow, concurred with the chosen answer, and have attempted to implement the algorithm using a console app in C# using a simple LINQ expression. My question is: how do I translate the "var result" of the lambda expression into a usable object that I c...
Hi. I want to use object instances as modules/functors, more or less as shown below: abstract class Lattice[E] extends Set[E] { val minimum: E val maximum: E def meet(x: E, y: E): E def join(x: E, y: E): E def neg(x: E): E } class Calculus[E](val lat: Lattice[E]) { abstract class Expr case class Var(name: String) extends...
I have a problem using a parameterized class as the key-type of a Map. First create the parameterized class: scala> sealed abstract class Foo[T]{ def t: T } defined class Foo Now create some imaginary collection of these across unknown parameters: scala> var l: List[Foo[_]] = Nil l: List[Foo[_]] = List() Now create a Map to store ...
Does "Value Restriction" practically mean that there is no higher order functional programming? I have a problem that each time I try to do a bit of HOP I get caught by a VR error. Example: let simple (s:string)= fun rq->1 let oops= simple "" type 'a SimpleType= F of (int ->'a-> 'a) let get a = F(fun req -> id) let oops2= get "" ...
How does ML perform the type inference in the following function definition: let add a b = a + b Is it like C++ templates where no type-checking is performed until the point of template instantiation after which if the type supports the necessary operations, the function works or else a compilation error is thrown ? i.e. for example,...
I was playing around the other day with making a class to handle some arithmetic operations (yes, I know numeric is coming out in 2.8) and found myself wondering how to simplify the following: def Foo[A]( _1:A, _2:A ) = (_1, _2) match{ case _1:Bar, _2:Bar => _1 + _2 case _1:Baff, _2:Baff => _1 push _2 case _, _ => None } s...
Consider the following declaration of a generic utility class in Delphi 2010: TEnumerableUtils = class public class function InferenceTest<T>(Param: T): T; class function Count<T>(Enumerable: TEnumerable<T>): Integer; overload; class function Count<T>(Enumerable: TEnumerable<T>; Filter: TPredicate<T>): Integer; overload; end; So...
I would like to write an object generator for a templated RAII class -- basically a function template to construct an object using type deduction of parameters so the types don't have to be specified explicitly. The problem I foresee is that the helper function that takes care of type deduction for me is going to return the object by ...
I have: class A { public: B toCPD() const; And: template<typename T> class Ev { public: typedef result_of(T::toCPD()) D; After instantiating Ev<A>, the compiler says: meta.h:12: error: 'T::toCPD' is not a type neither decltype nor typeof work either. ...
Why does this work? I'm not complaining, just want to know. void Test() { int a = 1; int b = 2; What<int>(a, b); // Why does this next line work? What(a, b); } void What<T>(T a, T b) { } ...
I am using the Entity Framework, ASP.NET and C#3.5 I borrowed the following code to make sorting possible using a sortExpression from a GridView instead of the property of an entity: public static IEnumerable<T> Sort<T>(this IEnumerable<T> source, string sortExpression) { string[] sortParts = sortExpression.Split(' '); ...
I'm kind of new in Haskell and I have difficulty understanding how inferred types and such works. map :: (a -> b) -> [a] -> [b] (.) :: (a -> b) -> (c -> a) -> c -> b What EXACTLY does that mean? foldr :: (a -> b -> b) -> b -> [a] -> b foldl :: (a -> b -> a) -> a -> [b] -> a foldl1 :: (a -> a -> a) -> [a] -> a What are the differenc...
I've got this code that works: def testTypeSpecialization: String = { class Foo[T] def add[T](obj: Foo[T]): Foo[T] = obj def addInt[X <% Foo[Int]](obj: X): X = { add(obj) obj } val foo = addInt(new Foo[Int] { def someMethod: String = "Hello world" }) foo.someMethod } But, I'd lik...
foldr:: (a -> b -> b) -> b -> [a] -> b map :: (a -> b) -> [a] -> [b] mys :: a -> a (.) :: (a -> b) -> (c -> a) -> c -> b what is inferred type of: a.map mys :: b.mys map :: c.foldr map :: d.foldr map.mys :: I've tried to create mys myself using mys n = n + 2 but the type of that is mys :: Num a => a -> a What's the difference bet...