casting

问题 let json = [ "left" : 18, "deadline" : "May 10", "progress" : 0.6 ] as [String: AnyObject] let ss = json["progress"] as? Float let sss = json["progress"] as? Double print("ss = \(ss)\n sss = \(sss)") I have no idea why the ss shows nil while sss shows 0.599999998 . Why does casting to Float get nil? Do you guys have some methods so that I can get the correct result? 回答1: The 0.6 is a Double literal value . As such, you can't cast it to Float (you need to convert it). Try this instead: let f =

问题 I'm getting some weirdness when I'm casting a Dynamic Proxy Class to the object I want it to be. At runtime, under certain conditions, I receive a ClassCastException. In order to explain this better, here are the definitions for the classes/interfaces I want to use. Brackets have been put around any extended interfaces that (should be) irrelevant. public interface CommandSender (extends Permissible) public interface ConsoleCommandSender extends CommandSender, (Conversable) public interface

问题 This question already has an answer here : Closed 7 years ago . Possible Duplicate: SWIG Java Retaining Class information of the objects bouncing from C++ Question : Why is my C++ swigged object losing its type when passed to a Java callback function? Setup : I've taken the Swig Java example for doing callbacks and added an object to be passed to the callback run(Parent p) . The callback works as expected but when I pass a Child object the Java seems to lose its type and think its of type

问题 After reading through a lot of questions, I asked myself if it is possible to solve the dilemma of transforming a string into a generic number WITHOUT using a hardcoded approach. For example: I get from a method a parameter with the type Class With Number.isAssignableFrom or other ways I can check, if this is a number class. But I also get from the user an input. As a string. The question is: Can I now somehow transform this string into the requested number object without building an if

问题 I am unable to cast a generic type to another generic type, besides the cast should be valid What I want to archive is in short (for MyModel implementing IModel , and MyImplementation implementing IImplementation ): IImplementation<IModel> implementation = new MyImplementation<MyModel>(); Assert.IsNull(implementation as IImplementation<IModel>); This is a bit confusing, as the type should be valid. Complete conceptual model: interface IModel {} class MyModel : IModel {} interface

问题 This question already has answers here : Casting between two types derived from the (same) interface (9 answers) Casting between classes that share the same interface (7 answers) Casting a interface derived class to another derived class (1 answer) Closed 10 months ago . I have 2 classes which implement the same interface. But somehow I cannot cast them from one to another. Here's an example: public interface IObject { // ... } public class FooObject : IObject { // ... } public class

问题 I have a problem with casting a generic class to the interface it is implementing. My code is like this: interface foo { void foobar(); } class bar: foo { public void foobar() { throw new NotImplementedException(); } } now I have my factory that creates instances of my classes by the interface, mostly a simple microkernel (service locator). I will simplify it here. Normally it will look up the implementing class from the configs and the factory take the type as T but that doesn't matter for

问题 I implemented an explicit conversion from string to object called Foo. So => Foo f = (Foo)"foo data"; works I need to implement a function that cast a string to the generic T, T in this case is Foo datatype. public T Get<T>(object o){ // this always return false if (typeof(T).IsAssignableFrom(typeof(String))) { // when i by pass the if above this throws invalid cast exception return (T)(object)str; } return null; } // When I call this, it generated an error // Invalid cast from 'System.String

问题 I want to create a map that will provide the benefits of generics, whilst supporting multiple different types of values. I consider the following to be the two key advantages of generic collections: compile time warnings on putting wrong things into the collection no need to cast when getting things out of collections So what I want is a map: which supports multiple value objects, checks values put into the map (preferably at compile-time) knows what object values are when getting from the

问题 Given a df in semi-long format with id variables a and b and measured data in columns m1 and m2 . The type of data is specified by the variable v (values var1 and var2). set.seed(8) df_l <- data.frame( a = rep(sample(LETTERS,5),2), b = rep(sample(letters,5),2), v = c(rep("var1",5),rep("var2",5)), m1 = sample(1:10,10,F), m2 = sample(20:40,10,F)) Looks as: a b v m1 m2 1 W r var1 3 40 2 N l var1 6 32 3 R a var1 9 28 4 F g var1 5 21 5 E u var1 4 38 6 W r var2 1 35 7 N l var2 8 33 8 R a var2 10 29