boxing

I almost understand why this particular problem arises (though I more than welcome a layman's explanation if you can find the time!), it I'm sure involves boxing/unboxing which I won't attempt to incorrectly explain.. With my current knowledge (or lack thereof), of the situation, I'm not sure how best to proceed to resolve it. Here is a fairly simplified console app showing my issue: static void Main(string[] args) { try { // succeeds IEnumerable<Expression<Func<TestCase1Impl, dynamic>>> results1 = typeof(ITestCase1).GetMethods().Select(m => buildDynamicExpression(new TestCase1Impl(), m));

Integer i = null; if (i == 3) Why the second line above throws a NullPointerException , IMHO, this has only one meaning which is Wrapper Object i is to be unboxed which yields the Exception such as: ArrayList<Integer> list = new ArrayList<Integer>(); list.add(null); int x = list.get(0); EDIT: Can you supply me with some format doc? It throws NPE because compiler does the following "magic" for you: Integer i = null; if (i.intValue() == 3) Obviously i.intValue() throws NPE when i is null . Think of the wrapper class to be a holder object. Something like: public class Integer { private int

The code I'm writing receives an ArrayList from unmanaged code, and this ArrayList will always contain one or more objects of type Grid_Heading_Blk. I've considered changing this ArrayList to a generic List, but I'm unsure if the conversion operation will be so expensive as to nullify the benefits of working with the generic list. Currently, I'm just running a foreach (Grid_Heading_Blk in myArrayList) operation to work with the ArrayList contents after passing the ArrayList to the class that will use it. Should I convert the ArrayList to a generic typed list? And if so, what is the most

In the below code, the statement 1 throws casting exception. I am wondering why isnt it unboxing? The statement 2 works fine but I want to know why the first one is wrong? using (IDbCommand command = connection.CreateCommand()) { command.CommandText = string.Format("SELECT COUNT(1) FROM {0}", tableName); int count = (int)command.ExecuteScalar(); //statement 1 } //int count = Convert.ToInt32(command.ExecuteScalar()); //statement 2 Sigh, execute scalar returns a long/int64, seeing as you wrote the SQL command you know the return vale is going to be a computed whole number (SELECT COUNT(..., also

Previously a question was asked about creating an array of functions where the functions returned integers from a range. The final solution was to do a map/collect into a Vec<_> . I have a similar yet different situation where I have closures with the same signature but different implementations. I tried this: let xs: Vec<_> = vec![ move |(x, y)| (y, x), move |(x, y)| (1 - y, 1 - x), ]; The error I get back: error[E0308]: mismatched types --> src/main.rs:4:9 | 4 | move |(x, y)| (1 - y, 1 - x), | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected closure, found a different closure | = note: expected type `

public void DoSomething(params object[] args) { // ... } The problem with the above signature is that every value-type that will be passed to that method will be boxed implicitly, and this is serious performance issue for me. Is there a way to declear a method that accepts variable number of arguments without boxing the value-types? Thanks. You can use generics: public void DoSomething<T>(params T[] args) { } However, this will only allow a single type of ValueType to be specified. If you need to mix or match value types, you'll have to allow boxing to occur, as you're doing now, or provide

I'm creating a messaging system for use in an XNA game. My Message types are structs because I want them to behave in a Value Type way. struct MyMessageType1 : IMessage {} struct MyMessageType2 : IMessage {} List<IMessage> messageQueue = new List<IMessage>(); I want to be able to store Messages of different types in my message queue, but I want to do so without any of them being boxed. If I have the structs implement an interface such as IMessage and I try to store them in a List, they get boxed. I don't know all the possible message types ahead of time, so I can't just hard code one List for