Haskell uses Hindley-Milner type inference algorithm whereas Scala, in order to support Object Oriented side of things, had to forgo using it for now. In order to write an add function for all applicable types easily, you will need to use Scala 2.8.0: Welcome to Scala version 2.8.0.r18189-b20090702020221 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_15). … Read more
This is actually a legitimate type inference*. We can reduce this to the following example (Ideone): interface Foo { <F extends Foo> F bar(); public static void main(String[] args) { Foo foo = null; String baz = foo.bar(); } } The compiler is allowed to infer a (nonsensical, really) intersection type String & Foo because Foo is … Read more
As of TS3.4 there is no partial type parameter inference. Either you let the compiler try to infer all the type parameters, or you specify all the type parameters. (Well, there are default type parameters but that doesn’t give you what you want: you want to infer the type parameters you leave out, not assign … Read more
Yes, I also found this quite surprising. Double conforms to both FloatLiteralConvertible and IntegerLiteralConvertible (ExpressibleByFloatLiteral and ExpressibleByIntegerLiteral in Swift 3). Therefore a Double can be initialized with floating point literal let a = 3.0 or with an integer literal: let b : Double = 10 (The same is true for other floating point types like … Read more
Just above that example, it says if e is an unparenthesized id-expression or a class member access (5.2.5), decltype(e) is the type of the entity named by e. if e is an lvalue, decltype(e) is T&, where T is the type of e; I think decltype(a->x) is an example of the “class member access” and … Read more
Q: Why doesn’t toSet do what I want? A: That would be too easy. Q: But why doesn’t this compile? List(1).toSet.map(x => …) A: The Scala compiler is unable to infer that x is an Int. Q: What, is it stupid? A: Well, List[A].toSet doesn’t return an immutable.Set[A]. It returns an immutable.Set[B] for some unknown … Read more
Well, it turned out that Rob Napier was right. It was one single file (actually one method) that was causing the compiler to go berzek. Now don’t get me wrong. Swift does recompile all your files each time, but the great thing now, is that Apple added real-time compilation feedback over the files it compiles, … Read more
I wanted to create an extension method that could enumerate over a list of things, and return a list of those things that were of a certain type. It would look like this: listOfFruits.ThatAre<Banana>().Where(banana => banana.Peel != Color.Black) … Sadly, this is not possible. The proposed signature for this extension method would have looked like: … Read more
After your update: no. There is no such functionality in C++. The closest is macros: #define AUTO_ARG(x) decltype(x), x f.bar<AUTO_ARG(5)>(); f.bar<AUTO_ARG(&Baz::bang)>(); Sounds like you want a generator: template <typename T> struct foo { foo(const T&) {} // do whatever }; template <typename T> foo<T> make_foo(const T& x) { return foo<T>(x); } Now instead of spelling … Read more
Inference doesn’t consider the return type; you can, however, try splitting the generics; for example, you could write code to allow: .Cast().To<Type2>() by having (untested; indicative only) public static CastHelper<T> Cast<T>(this T obj) { return new CastHelper<T>(obj); } public struct CastHelper<TFrom> { private readonly TFrom obj; public CastHelper(TFrom obj) { this.obj = obj;} public TTo … Read more