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• Is it possible to use the values method for a HashMap if the values are ArrayLists?

  - by Denman

  I'm stuck trying to get something to work in an assignment. I have a HashMap<Integer, ArrayList<Object>> called sharedLocks and I want to check whether a certain value can be found in any ArrayList in the HashMap. The following code obviously wouldn't work because Object[] can't be cast to ArrayList[], but it is a demonstration of the general functionality that I want. ArrayList[] values = (ArrayList[]) sharedLocks.values().toArray(); boolean valueExists = false; for (int i = 0; i < values.length; i++) { if (values[i].contains(accessedObject)) { valueExists = true; } } Is there a way for me to check every ArrayList in the HashMap for a certain value? I'm not sure how to use the values method for HashMaps in this case. Any help would be much appreciated.

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• Core Data: Detecting the type and casting it

  - by Tim Sullivan

  I have set up a Core Data model that includes an entity, Item with a 1-M relationship with the abstract entity Place, so that an item has many places. There are several entities with the parent set to Place. I want to set up several UI elements depending on the descendent place types. I have a loop that looks something like this: for (Place *place in item.places) { } ... but I'm not sure how to detect what type the place is, and how to cast it to the proper type so that I can access its properties. Thanks for any help!

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• define macro in C wont work

  - by Spidfire

  Im trying to make a macro in C that can tell if a char is a hex number ( 0-9 a-z A-Z) #define _hex(x) (((x) >= "0" && (x) <= "9" )||( (x) >= "a" && (x) <= "z") || ((x) >= "A" && (x) <= "Z") ? "true" : "false") this what ive come up with but it wont work with a loop like this char a; for(a = "a" ; a < "z";a++){ printf("%s => %s",a, _hex(a)); } but it gives a error test.c:8: warning: assignment makes integer from pointer without a cast test.c:8: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer test.c:9: warning: comparison between pointer and integer

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• How can I pass a type as a parameter in scala?

  - by rsan

  I'm having a really hard time trying to figure out how can I store or pass a type in scala. What I want to achive is something like this: abstract class Foo( val theType : type ) object Foo{ case object Foo1 extends Foo(String) case object Foo2 extends Foo(Long) } So at some point I can do this: theFoo match{ case String => "Is a string" case Long => "Is a long" } and when obtaining the object being able to cast it: theFoo.asInstanceOf[Foo1.theType] Is this possible? If is possible, is a good aproach? What I'm trying to achieve ultimately is writing a pseudo schema for byte stream treatment. E.g if I have an schema Array(Foo1,Foo1,Foo2,Foo3,Foo1) I could parse Arrays of bytes that complain with that schema, if at some point I have a different stream of bytes I could just write a new schema Array(Foo3, Foo4, Foo5) without having to reimplement parsing logic. Regards,

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• Java generic function for performing calculations on integer, on double?

  - by Daniel

  Is this possible? Surely if you passed in a double, any sort of function implementation code which casts an object to an Integer would not be able to work unless the cast 'Integer' was specifically used? I have a function like: public static void increment(Object o){ Integer one = (Integer)o; system.out.println(one++); } I cant see how this could be made generic for a double? I tried public static <E> void increment(E obj){ E one = (E)o; system.out.println(one++); } but it didn't like it?

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• A strange error in java generic.

  - by ???

  This is ok: Class<? extends String> stringClass = "a".getClass(); But this gets error: <T> void f(T obj) { Class<? extends T> objClass = obj.getClass(); } I know I can cast it like: <T> void f(T obj) { @SuppressWarnings("unchecked") Class<? extends T> objClass = (Class<? extends T>) obj.getClass(); } But why the previous error? Will the next release of Java 7 will support such usage?

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• A Solution For (IEnumerable<Base>)Derive; Yet?

  - by acidzombie24

  I have D1 and D2 which derive from B. When i write var ls = (IEnumerable<B>)(cond?lsD1:lsD2); I get a runtime cast error. IIRC this is a well known problem. My question is 1) Is this allowed yet? perhaps in .NET 4? I have 2010 but my project is a few months old, large and targets 3.5. 2) Is there a simple workaround? I only need to read the list not add anything or remove. Actually, ToArray() would probably work but is there another solution?

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• Determine an object's class returned by a factory method (Error: function does not take 1 arguments

  - by tzippy

  I have a factorymethod that either returns an object of baseclass or one that is of derivedclass (a derived class of baseclass). The derived class has a method virtual void foo(int x) that takes one argument. baseclass however has virtual void foo() without an argument. In my code, a factory method returns a pointer of type bar that definetly points to an object of class derivedclass. However since this is only known at runtime I get a compiler error saying that foo() does not take an argument. Can I cast this pointer to a pointer of type derivedclass? std::auto_ptr<baseclass> bar = classfactory::CreateBar(); //returns object of class derivedclass bar->foo(5); class baseclass { public: virtual void foo(); } class derivedclass : public baseclass { public: virtual void foo(int x); }

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• Proc causing a random TypeError

  - by go____yourself

  I'm refactoring some code and this proc is causing an error randomly and I don't know why or how to debug it... Any ideas? New code with proc defense_moves, offense_moves = [], [] determine_move = ->move,side,i { side << move.count(move[i]) } defense.size.times { |i| determine_move.(defense, defense_moves, i) } offense.size.times { |i| determine_move.(offense, offense_moves, i) } dm = defense[defense_moves.index(defense_moves.max)].nil? ? [0] : defense[defense_moves.index(defense_moves.max)] om = offense[offense_moves.index(offense_moves.max)].nil? ? [0] : offense[offense_moves.index(offense_moves.max)] Original code: d = 0 defense_moves = [] loop do defense_moves << defense.count(defense[d]) break if defense.count(defense[d]).zero? d += 1 end o = 0 offense_moves = [] loop do offense_moves << offense.count(offense[o]) break if offense.count(offense[o]).zero? o += 1 end dm = defense[defense_moves.index(defense_moves.max)].nil? ? [0] : defense[defense_moves.index(defense_moves.max)] om = offense[offense_moves.index(offense_moves.max)].nil? ? [0] : offense[offense_moves.index(offense_moves.max)] TypeError ttt2.rb:95:in `[]': no implicit conversion from nil to integer (TypeError) from ttt2.rb:95:in `computer_make_move' from ttt2.rb:133:in `draw_board' from ttt2.rb:24:in `place' from ttt2.rb:209:in `block in start_new_game' from ttt2.rb:188:in `loop' from ttt2.rb:188:in `start_new_game' from ttt2.rb:199:in `block in start_new_game' from ttt2.rb:188:in `loop' from ttt2.rb:188:in `start_new_game' from ttt2.rb:199:in `block in start_new_game' from ttt2.rb:188:in `loop' from ttt2.rb:188:in `start_new_game' from ttt2.rb:199:in `block in start_new_game' from ttt2.rb:188:in `loop' from ttt2.rb:188:in `start_new_game' from ttt2.rb:199:in `block in start_new_game' from ttt2.rb:188:in `loop' from ttt2.rb:188:in `start_new_game' from ttt2.rb:234:in `<main>'

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• What do C# Table Adapters actually return?

  - by Raven Dreamer

  I'm working on an application that manipulates SQL tables in a windows form application. Up until now, I've only been using the pre-generated Fill queries, and self-made update and delete queries (which return nothing). I am interested in storing the value of a single value from a single column (an 'nchar(15)' name), and though I have easily written the SQL code to return that value to the application, I have no idea what it will be returned as. SELECT [Contact First Name] FROM ContactSkillSet WHERE [Contact ID] = @CurrentID Can the result be stored directly as a string? Do I need to cast it? Invoke a toString method?

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• Using "as" and expecting a null return

  - by DrLazer

  For example. Lets say we have a stackpanel on a form. Its full of both Grids and Labels. I want to loop through all the Grids and do some operation on them but leave the Lables intact. At the moment I am doing it this way. foreach(UIElement element in m_stacker.Children) { Grid block = element as Grid; if(block != null) { //apply changes here } } So i'm using the fact that "as" returns null if it cannot cast into the required type. Is this an ok thing to do or is there a better solution to this problem?

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• I just don't get the C++ Pointer/Reference system.

  - by gnm

  I've never had problems with references as in Python (implicit) or PHP (explicit &). In PHP you write $p = &$myvar; and you have $p as a reference pointing to $myVar. So I know in C++ you can do this: void setToSomething( int& var ) { var = 123; } int myInt; setToSomething( myInt ); Myint is now 123, why? Doesn't & mean "memory address of" x in C++? What do I do then if var is only the adress to myInt and not a pointer? void setToSomething( int* var ) { var* = 123; } int myInt; int* myIntPtr = &myInt; setToSomething( myIntPtr ); Does the above work as expected? I don't understand the difference between * and & in C++ fully. They tell you & is used to get the adress of a variable, but why IN GODS NAME does that help you in functions etc. like in the first example?

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• Is void *p = 0L valid?

  - by Artefacto

  In this answer, sassman initializes a pointer with: zend_class_entry* ce = 0L; My question is – is this valid? I would say it isn't, to initialize the variable with a null pointer either an unadorned (and possibly casted to void *) 0 constant, or some macro that evaluates to that such as NULL should be used. However, I can't find definitive language in the standard that supports this interpretation. All it says is: An integer constant expression with the value 0, or such an expression cast to type void *, is called a null pointer constant.

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• Casting in mixed type calculations in C?

  - by yCalleecharan

  Hi, If I define these variables: double x0, xn, h; int n; and I have this mathematical expression: h = (xn - x0)/n; Is it necessary that I cast n into double prior doing the division for maximum accuracy like in h = (xn - x0)/ (double) n; I wrote a program to check the above but both expressions give the same answers. I understand that C will promote the integer to double type as variables xn and x0 are of type double but strangely enough in a book, the second expression with casting was emphasized. Thanks a lot...

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• Wherewith replace Dictionary.Where(p => p.Key is T)

  - by abatishchev

  I have a System.Collections.Generic.Dictionary<System.Web.UI.Control, object> where all keys can be either type of System.Web.UI.WebControls.HyperLink or type of System.Web.UI.WebControls.Label. I want to change Text property of each control. Because HyperLink doesn't implement (why??) ITextControl, I need to cast Label or HyperLink explicitly: Dictionary<Control,object> dic = .. dic .Where(p => p.Key is HyperLink) .ForEach(c => ((HyperLink)c).Text = "something") dic .Where(p => p.Key is Label) .ForEach(c => ((Label)c).Text = "something") Are there ways to workaround such approach?

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• error message fix

  - by user1722654

  for (int i = 0; i < dataGridView1.Rows.Count; i++) { //bool sleected = false; if (dataGridView1.Rows[i].Cells[3].Value != null) { selected.Add(i); } } //string donew = ""; // line off error textBox1.Text = ((String)dataGridView1.Rows[1].Cells[2].Value); /* for (int i = 0; i < selected.Count; i++) { textAdded.Add((String)dataGridView1.Rows[0].Cells[2].Value); // donew += (String)dataGridView1.Rows[selected[i]].Cells[2].Value; }*/ I keep getting the error Unable to cast object of type 'System.Double' to type 'System.String' What can I do to overcome this?

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• C++ Inheritance Question

  - by shaz

  I have a base class MessageHandler and 2 derived classes, MessageHandler_CB and MessageHandler_DQ. The derived classes redefine the handleMessage(...) method. MH_DQ processes a message and puts the result in a deque while MH_CB processes the message and then executes a callback function. The base class has a static callback function that I pass along with a this pointer to a library which calls the static callback when a new message is available for processing. My problem comes when I am in the static callback with a void * pointing to either a MH_DQ or a MH_CB. If I cast it to the base class the empty MessageHandler::handleMessage(...) method is called, rather than the version in the appropriate derived class. What is the best way to address this situation from a design perspective and/or what language features might help me to implement a solution to my problem? Thanks in advance!

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• Getting the fractional part of a float without using modf()

  - by knight666

  Hi, I'm developing for a platform without a math library, so I need to build my own tools. My current way of getting the fraction is to convert the float to fixed point (multiply with (float)0xFFFF, cast to int), get only the lower part (mask with 0xFFFF) and convert it back to a float again. However, the imprecision is killing me. I'm using my Frac() and InvFrac() functions to draw an anti-aliased line. Using modf I get a perfectly smooth line. With my own method pixels start jumping around due to precision loss. This is my code: const float fp_amount = (float)(0xFFFF); const float fp_amount_inv = 1.f / fp_amount; inline float Frac(float a_X) { return ((int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } inline float Frac(float a_X) { return (0xFFFF - (int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } Thanks in advance!

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• C++, is it possible to obtain the dimension of an array?

  - by aaa

  hi. Suppose I have some pointer, which I want to reinterpret as static dimension array reference: double *p; double (&r)[4] = ?(p); // some construct? // clarify template< size_t N> void function(double (&a)[N]); ... double *p; function(p); // this will not work. // I would like to cast p as to make it appear as double[N] Is it possible to do so? how do I do it?

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• Is it possible in Scala to force the caller to specify a type parameter for a polymorphic method ?

  - by Alex Kravets

  //API class Node class Person extends Node object Finder { def find[T <: Node](name: String): T = doFind(name).asInstanceOf[T] } //Call site (correct) val person = find[Person]("joe") //Call site (dies with a ClassCast inside b/c inferred type is Nothing) val person = find("joe") In the code above the client site "forgot" to specify the type parameter, as the API writer I want that to mean "just return Node". Is there any way to define a generic method (not a class) to achieve this (or equivalent). Note: using a manifest inside the implementation to do the cast if (manifest != scala.reflect.Manifest.Nothing) won't compile ... I have a nagging feeling that some Scala Wizard knows how to use Predef.<:< for this :-) Ideas ?

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• How to do hex8 encoding in c?

  - by Tech163

  I am trying to encode a string in hex8 using c. The script I have right now is: int hex8 (char str) { str = printf("%x", str); if(strlen(str) == 1) { return printf("%s", "0", str); } else { return str; } } In this function, I will need to add a 0 ahead of the string if the length is less than 1. I don't know why I'm getting: passing argument 1 of 'strlen' makes pointer from integer without a cast Does anyone know why?

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• Upcasting in C#: Making a Fruit a Pear

  - by Adam Kane

  Why can't I upcast (?) a Fruit to a Pear? public static class PearGenerator { public static Pear CreatePear () { // Make a new generic fruit. Fruit genericFruit = new Fruit(); // Upcast it to a pear. (Throws exception: Can't cast a Fruit to a Pear.) Pear pear = (Pear)genericFruit; // Return freshly grown pear. return ( pear ); } } public class Fruit { // some code } public class Pear : Fruit { public void PutInPie () { // some code } } Thanks!

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• C# Why does calling an interface member from a class generate an error?

  - by Jack

  So I have an interface: interface IFoo { int Bar(); int this[int i] {get; set;} } And a class that derives from it class Foo : IFoo { public int IFoo.Bar() { //Implementation { public int IFoo.this[int i] { //Implementation } } Now, I try to do this: var fooey = new Foo(); int i = Fooey.Bar(); or this: int i = Fooey[4]; I would expect these to work properly. However, the compiler generates an error as if such members don't exist. Why is that? I am aware I can cast Foo as IFoo, but I am also aware that casting is costly to performance, which is often the reason to use interfaces in the first place. EDIT 1: These are the errors generated 'Foo' does not contain a definition for 'Bar' and no extension method 'Bar' accepting a first argument of type 'Foo' could be found (are you missing a using directive or an assembly reference?) "Cannot apply indexing to an expression of type 'Foo'"

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• Network license control for a Java application

  - by user1461615

  I have been tasked with providing some form of network license control for a Java application. The app would be stored on a network drive and run from a client machine. The basic idea is that it will be able to work out how many times it is being run concurrently and prevent the N+1th user from running the software where N is the number of concurrent licenses the customer has purchased. Is this possible somehow with a Java application? I implemented a "solution" which relied on multi-cast UDP communication between the running instances of the application but this didn't work because on most networks this kind of communication is blocked by security measures. Is there a better way? I don't even mind if it requires JNI/JNA. N.B. The solution does not have to be that sophisticated or highly secure.

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• Does C# 4's covariance support nesting of generics?

  - by Scott Bilas

  I don't understand why 'x' below converts, but 'y' and 'z' do not. var list = new List<List<int>>(); IEnumerable<List<int>> x = list; List<IEnumerable<int>> y = list; IEnumerable<IEnumerable<int>> z = list; Does the new covariance feature simply not work on generics of generics or am I doing something wrong? (I'd like to avoid using .Cast< to make y and z work.)

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