casting

问题 Consider this static test class: public static class Test { public static ushort sum(ushort value1, ushort value2) { return value1 + value2 } } This causes the following compile error, with value1 + value2 underlined in red: Cannot implicitly convert type 'int' to 'ushort'. An explicit conversion exists (are you missing a cast)? Why? 回答1: Like C and C++ before it, integers are implicitly widened when used with many operators. In this case, the result of adding two ushort values together is

问题 I have Message class which I have extended and added new property. class ChildMessage: Message { prop... } While trying to add Message Class to ChildMessage list I get Null reference for added class. var myChildList =new List<ChildMessage> (); var myParentClass = new Message(); myChildList.add(myParentClass as ChildMessage) myChildList[0] == null //Always return null What is wrong with my code? What are the alternatives? 回答1: It is because a true instance of Message is not a ChildMessage ,

问题 I have swift array of tuples [(String, String)] and would like to cast this array to NSMutableArray. I have tried this and it is not working: let myNSMUtableArray = swiftArrayOfTuples as! AnyObject as! NSMutableArray 回答1: Since swift types like Tuple or Struct have no equivalent in Objective-C they can not be cast to or referenced as AnyObject which NSArray and NSMutableArray constrain their element types to. The next best thing if you must return an NSMutableArray from a swift Array of

问题 I have a query that ought to return an IQueryable<MyType> . The code looks like this: public IQueryable<MyType> GetFooList() { var query = (from x in dbContext.TableX join y in dbContext.TableY on x.our_id equals y.our_id join z in dbContext.TableZ on y.our_id equals z.our_id join a in dbContext.TableA on z.other_id equals a.other_id where !string.IsNullOrEmpty(x.status) select new { (fields....) }) .AsQueryable(); IQueryable<MyType> result = (IQueryable<MyType>) query; return result; } In

问题 I have been working on a query to generate xml from the oracle database database where "column" is a type CREATE OR REPLACE TYPE "column" AS OBJECT ("coulmnname" VARCHAR2 (30), "datatype" VARCHAR2 (30)) and col_list_t is of type CREATE OR REPLACE TYPE col_list_t AS TABLE OF "column" and SELECT CAST ( MULTISET ( SELECT "column" (B.COLUMN_NAME, B.DATA_TYPE) FROM all_tab_columns b, all_tables c ,all_tables a WHERE b.TABLE_NAME = a.TABLE_NAME AND b.table_name = c.TABLE_NAME AND B.OWNER = C.OWNER

问题 This question already has answers here : Why does “true” == true show false in JavaScript? (3 answers) Closed 4 years ago . This small portion of code took a long time to be noticed. I thought if I do the following, it would be fine if('true' == true) { alert("Does not happen"); } But it does not pass the if condition. I thought the double equals == matches the value not the type as matching the type is the job of === . Now my questions are why wasn'the true typecast to 'true' or why is it

问题 I've recently started coding with Akka/Scala, and I've run into the following problem: With a implicit conversion in scope, such as: implicit def convertTypeAtoTypeX(a: TypeA): TypeX = TypeX() // just some kinda conversion This works: returnsAFuture.mapTo[TypeX].map { x => ... } But this doesn't: returnsAFuture.mapTo[TypeX].onComplete { ... } The latter fails with a type cast exception. (i.e. TypeA cannot be cast to TypeX) Very confused. Why? I suspect it has something to do with Try, but I

问题 I use a Java lib that relies on exceptions. Simplified code below: try { val eventTime = eventTimeString.as[Date] } catch { case e: Exception => logger.error(s"Can't parse eventTime from $eventTimeString", e) // take action for the bad Date string. } In Java I would catch only the exception from parsing a string into a Date, letting the rest go uncaught since they could be fatal. Here my understanding is that catching Exception means to catch ANY non-fatal/non-serious exceptions. Since it is

问题 I do not believe that it is possible to completely avoid C-style casts when writing C++. I was surprised to find out that I needed to use a C-style cast to avoid a compiler truncation warning: short value_a = 0xF00D; // Truncation warning in VS2008 short value_b = static_cast<short>(0xF00D); // Truncation warning in VS2008 short value_c = (short)0xF00D; // No warning! Are there other scenarios where there is no C++-style substitute for a C-style cast? 回答1: You are just trying to obfuscate

问题 I've been busy with C# 4.0 generics, and now I basically want to do something like this: public abstract class GenericTree<T> : Tree where T : Fruit { public Tree(IFruitCollection<T> fruits) : base(fruits) { } } The base Tree class looks like this: public abstract class Tree { private IFruitCollection<Fruit> fruits; public IFruitCollection<Fruit> GetFruits { get { return fruits; } } public Tree(IFruitCollection<Fruit> fruits) { this.fruits = fruits; } } Here is my first problem. The