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  • Linked List Design

    - by Jim Scott
    The other day in a local .NET group I attend the following question came up: "Is it a valid interview question to ask about Linked Lists when hiring someone for a .NET development position?" Not having a computer sciense degree and being a self taught developer my response was that I did not feel it was appropriate as I in 5 years of developer with .NET had never been exposed to linked lists and did not hear any compeling reason for a use for one. However the person commented that it is a very common interview question so I decided when I left that I would do some reasearch on linked lists and see what I might be missing. I have read a number of posts on stack overflow and various google searches and decided the best way to learn about them was to write my own .NET classes to see how they worked from the inside out. Here is my class structure Single Linked List Constructor public SingleLinkedList(object value) Public Properties public bool IsTail public bool IsHead public object Value public int Index public int Count private fields not exposed to a property private SingleNode firstNode; private SingleNode lastNode; private SingleNode currentNode; Methods public void MoveToFirst() public void MoveToLast() public void Next() public void MoveTo(int index) public void Add(object value) public void InsertAt(int index, object value) public void Remove(object value) public void RemoveAt(int index) Questions I have: What are typical methods you would expect in a linked list? What is typical behaviour when adding new records? For example if I have 4 nodes and I am currently positioned in the second node and perform Add() should it be added after or before the current node? Or should it be added to the end of the list? Some of the designs I have seen explaining things seem to expose outside of the LinkedList class the Node object. In my design you simply add, get, remove values and know nothing about any node object. Should the Head and Tail be placeholder objects that are only used to define the head/tail of the list? I require my Linked List be instantiated with a value which creates the first node of the list which is essentially the head and tail of the list. Would you change that ? What should the rules be when it comes to removing nodes. Should someone be able to remove all nodes? Here is my Double Linked List Constructor public DoubleLinkedList(object value) Properties public bool IsHead public bool IsTail public object Value public int Index public int Count Private fields not exposed via property private DoubleNode currentNode; Methods public void AddFirst(object value) public void AddLast(object value) public void AddBefore(object existingValue, object value) public void AddAfter(object existingValue, object value) public void Add(int index, object value) public void Add(object value) public void Remove(int index) public void Next() public void Previous() public void MoveTo(int index)

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  • Turn class "Interfaceable"

    - by scooterman
    Hi folks, On my company system, we use a class to represent beans. It is just a holder of information using boost::variant and some serialization/deserialization stuff. It works well, but we have a problem: it is not over an interface, and since we use modularization through dlls, building an interface for it is getting very complicated, since it is used in almost every part of our app, and sadly interfaces (abstract classes ) on c++ have to be accessed through pointers, witch makes almost impossible to refactor the entire system. Our structure is: dll A: interface definition through abstract class dll B: interface implementation there is a painless way to achieve that (maybe using templates, I don't know) or I should forget about making this work and simply link everything with dll B? thanks Edit: Here is my example. this is on dll A BeanProtocol is a holder of N dataprotocol itens, wich are acessed by a index. class DataProtocol; class UTILS_EXPORT BeanProtocol { public: virtual DataProtocol& get(const unsigned int ) const { throw std::runtime_error("Not implemented"); } virtual void getFields(std::list<unsigned int>&) const { throw std::runtime_error("Not implemented"); } virtual DataProtocol& operator[](const unsigned int ) { throw std::runtime_error("Not implemented"); } virtual DataProtocol& operator[](const unsigned int ) const { throw std::runtime_error("Not implemented"); } virtual void fromString(const std::string&) { throw std::runtime_error("Not implemented"); } virtual std::string toString() const { throw std::runtime_error("Not implemented"); } virtual void fromBinary(const std::string&) { throw std::runtime_error("Not implemented"); } virtual std::string toBinary() const { throw std::runtime_error("Not implemented"); } virtual BeanProtocol& operator=(const BeanProtocol&) { throw std::runtime_error("Not implemented"); } virtual bool operator==(const BeanProtocol&) const { throw std::runtime_error("Not implemented"); } virtual bool operator!=(const BeanProtocol&) const { throw std::runtime_error("Not implemented"); } virtual bool operator==(const char*) const { throw std::runtime_error("Not implemented"); } virtual bool hasKey(unsigned int field) const { throw std::runtime_error("Not implemented"); } }; the other class (named GenericBean) implements it. This is the only way I've found to make this work, but now I want to turn it in a truly interface and remove the UTILS_EXPORT (which is an _declspec macro), and finally remove the forced linkage of B with A.

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  • iPhone SDK: Orientation (Landscape and Portrait views)

    - by domness
    Okay, I've got my normal app which is in portrait mode. I can force my app to go to landscape mode for a view (using navigationcontroller and viewcontroller) like this: - (void)viewWillAppear:(BOOL)animated { [[UIDevice currentDevice] setOrientation:UIInterfaceOrientationLandscapeRight]; } But then when I go back to the main menu (tableview) it goes straight back to portrait. I try this code: - (void)viewWillAppear:(BOOL)animated { [[UIDevice currentDevice] setOrientation:UIInterfaceOrientationPortrait]; } But that doesn't work.. Any ideas?

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  • Frustration with generics

    - by sbi
    I have a bunch of functions which are currently overloaded to operate on int and string: bool foo(int); bool foo(string); bool bar(int); bool bar(string); void baz(int p); void baz(string p); I then have a bunch of functions taking 1, 2, 3, or 4 arguments of either int or string, which call the aforementioned functions: void g(int p1) { if(foo(p1)) baz(p1); } void g(string p1) { if(foo(p1)) baz(p1); } void g(int p2, int p2) { if(foo(p1)) baz(p1); if(bar(p2)) baz(p2); } void g(int p2, string p2) { if(foo(p1)) baz(p1); if(bar(p2)) baz(p2); } void g(string p2, int p2) { if(foo(p1)) baz(p1); if(bar(p2)) baz(p2); } void g(string p2, string p2) { if(foo(p1)) baz(p1); if(bar(p2)) baz(p2); } // etc. (The implementation of the g() family is just a placeholder. actually they are more complicated.) More types than the current int or string might have to be introduced at any time. The same goes for functions with more arguments than 4. The current number of identical functions is barely manageable. Add one more variant in either dimension and the combinatoric explosion will be so huge, it might blow away the application. In C++, I'd templatize g() and be done. I understand that .NET generics are different. <sigh> But I have been fighting them for two hours trying to come up with a solution that doesn't involve too much copy&paste of code. To no avail. Surely, C#/.NET/generics/whatever won't require me to type out identical code for a family of functions taking five arguments of either of three types? So what am I missing here?

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  • Advantage of creating a generic repository vs. specific repository for each object?

    - by LuckyLindy
    We are developing an ASP.NET MVC application, and are now building the repository/service classes. I'm wondering if there are any major advantages to creating a generic IRepository interface that all repositories implement, vs. each Repository having its own unique interface and set of methods. For example: a generic IRepository interface might look like (taken from this answer): public interface IRepository : IDisposable { T[] GetAll<T>(); T[] GetAll<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter); T GetSingle<T>(Expression<Func<T, bool>> filter, List<Expression<Func<T, object>>> subSelectors); void Delete<T>(T entity); void Add<T>(T entity); int SaveChanges(); DbTransaction BeginTransaction(); } Each Repository would implement this interface (e.g. CustomerRepository:IRepository, ProductRepository:IRepository, etc). The alternate that we've followed in prior projects would be: public interface IInvoiceRepository : IDisposable { EntityCollection<InvoiceEntity> GetAllInvoices(int accountId); EntityCollection<InvoiceEntity> GetAllInvoices(DateTime theDate); InvoiceEntity GetSingleInvoice(int id, bool doFetchRelated); InvoiceEntity GetSingleInvoice(DateTime invoiceDate, int accountId); //unique InvoiceEntity CreateInvoice(); InvoiceLineEntity CreateInvoiceLine(); void SaveChanges(InvoiceEntity); //handles inserts or updates void DeleteInvoice(InvoiceEntity); void DeleteInvoiceLine(InvoiceLineEntity); } In the second case, the expressions (LINQ or otherwise) would be entirely contained in the Repository implementation, whoever is implementing the service just needs to know which repository function to call. I guess I don't see the advantage of writing all the expression syntax in the service class and passing to the repository. Wouldn't this mean easy-to-messup LINQ code is being duplicated in many cases? For example, in our old invoicing system, we call InvoiceRepository.GetSingleInvoice(DateTime invoiceDate, int accountId) from a few different services (Customer, Invoice, Account, etc). That seems much cleaner than writing the following in multiple places: rep.GetSingle(x => x.AccountId = someId && x.InvoiceDate = someDate.Date); The only disadvantage I see to using the specific approach is that we could end up with many permutations of Get* functions, but this still seems preferable to pushing the expression logic up into the Service classes. What am I missing?

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  • Is there a way to make ToEnum generic

    - by maxfridbe
    I would like to do this but it does not work. bool TryGetEnum<TEnum, TValue>(TValue value, out TEnum myEnum) { if (Enum.IsDefined(typeof(TEnum), value)) { myEnum = (TEnum)value; return true; } return false; } Example usage: MyEnum mye; bool success = this.TryGetEnum<MyEnum,char>('c',out mye);

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  • What is the difference between array parameters in C

    - by STeN
    Hi, what is the difference between following function declarations, which create and return the array in C/C++? Both methods create the array and fill it with proper values and returns true if everything passed. bool getArray(int* array); bool getArray(int* array[]); Thanks Best Regards, STeN

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  • Shaders with pygtkglext

    - by qba
    Do someone know how to get glsl shaders work in gtk-opengl window? With glut all glCreateProgram etc. functions works, but when I tried to put the same gl code into pygtkglext window, its complaining about NullReference: OpenGL.error.NullFunctionError: Attempt to call an undefined function glCreateProgram, check for bool(glCreateProgram) before calling So then I from OpenGL.GL.ARB.shader_objects import *, but the result is similar: OpenGL.error.NullFunctionError: Attempt to call an undefined function glCreateProgramObjectARB, check for bool(glCreateProgramObjectARB) before calling Any idea will be useful.

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  • Deriving from a component and implementing IDisposable properly

    - by PaulH
    I have a Visual Studio 2008 C# .NET 2.0 CF project with an abstract class derived from Component. From that class, I derive several concrete classes (as in my example below). But, when I go to exit my Form, though the Form's Dispose() member is called and components.Dispose() is called, my components are never disposed. Can anybody suggest how I can fix this design? public abstract class SomeDisposableComponentBase : Component { private System.ComponentModel.IContainer components; protected SomeDisposableComponentBase() { Initializecomponent(); } protected SomeDisposableComponentBase(IContainer container) { container.Add(this); Initializecomponent(); } private void InitializeComponent() { components = new System.ComponentModel.Container(); } protected abstract void Foo(); #region IDisposable Members bool disposed_; /// Warning 60 CA1063 : Microsoft.Design : Ensure that 'SomeDisposableComponentBase.Dispose()' is declared as public and sealed.* public void Dispose() { // never called Dispose(true); GC.SuppressFinalize(this); } protected virtual void Dispose(bool disposing) { // never called if (!disposed_) { if (disposing && (components != null)) { components.Dispose(); } disposed_ = true; } base.Dispose(disposing); } #endregion } public SomeDisposableComponent : SomeDisposableComponentBase { public SomeDisposableComponent() : base() { } public SomeDisposableComponent(IContainer container) : base(container) { } protected override void Foo() { // Do something... } protected override void Dispose(bool disposing) { // never called base.Dispose(disposing); } } public partial class my_form : Form { private SomeDisposableComponentBase d_; public my_form() { InitializeComponent(); if (null == components) components = new System.ComponentModel.Container(); d_ = new SomeDisposableComponent(components); } /// exit button clicked private void Exit_Click(object sender, EventArgs e) { this.Close(); } /// from the my_form.designer.cs protected override void Dispose(bool disposing) { if (disposing && (components != null)) { // this function is executed as expected when the form is closed components.Dispose(); } base.Dispose(disposing); } } *I note that FX-Cop is giving me a hint here. But, if I try to declare that function as sealed, I get the error: error CS0238: 'SomeDisposableComponentBase.Dispose()' cannot be sealed because it is not an override Declaring that function an override leads to: 'SomeDisposableComponentBase.Dispose()': cannot override inherited member 'System.ComponentModel.Component.Dispose()' because it is not marked virtual, abstract, or override Thanks, PaulH

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  • Does the type in this KVC validation method matter?

    - by dontWatchMyProfile
    For example, in the docs a KVC-style validation method is implemented like this: -(BOOL)validateAge:(id *)ioValue error:(NSError **)outError They used id* as the type for ioValue. Since that's not part of the method signature, I wonder if it would hurt to do something like: -(BOOL)validateAge:(NSNumber *)ioValue error:(NSError **)outError Is this still fine with KVC?

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  • Best way to test for a variable's existence in PHP; isset() is clearly broken

    - by chazomaticus
    From the isset() docs: isset() will return FALSE if testing a variable that has been set to NULL. Basically, isset() doesn't check for whether the variable is set at all, but whether it's set to anything but NULL. Given that, what's the best way to actually check for the existence of a variable? I tried something like: if(isset($v) || @is_null($v)) (the @ is necessary to avoid the warning when $v is not set) but is_null() has a similar problem to isset(): it returns TRUE on unset variables! It also appears that: @($v === NULL) works exactly like @is_null($v), so that's out, too. How are we supposed to reliably check for the existence of a variable in PHP? Edit: there is clearly a difference in PHP between variables that are not set, and variables that are set to NULL: <?php $a = array('b' => NULL); var_dump($a); PHP shows that $a['b'] exists, and has a NULL value. If you add: var_dump(isset($a['b'])); var_dump(isset($a['c'])); you can see the ambiguity I'm talking about with the isset() function. Here's the output of all three of these var_dump()s: array(1) { ["b"]=> NULL } bool(false) bool(false) Further edit: two things. One, a use case. An array being turned into the data of an SQL UPDATE statement, where the array's keys are the table's columns, and the array's values are the values to be applied to each column. Any of the table's columns can hold a NULL value, signified by passing a NULL value in the array. You need a way to differentiate between an array key not existing, and an array's value being set to NULL; that's the difference between not updating the column's value and updating the column's value to NULL. Second, Zoredache's answer, array_key_exists() works correctly, for my above use case and for any global variables: <?php $a = NULL; var_dump(array_key_exists('a', $GLOBALS)); var_dump(array_key_exists('b', $GLOBALS)); outputs: bool(true) bool(false) Since that properly handles just about everywhere I can see there being any ambiguity between variables that don't exist and variables that are set to NULL, I'm calling array_key_exists() the official easiest way in PHP to truly check for the existence of a variable. (Only other case I can think of is for class properties, for which there's property_exists(), which, according to its docs, works similarly to array_key_exists() in that it properly distinguishes between not being set and being set to NULL.)

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  • Logical equality in C

    - by andrew cooke
    [It seems odd this doesn't exist, so apologies in advance if it's a duplicate] I want to test for logical equality in C. In other words, I want to know whether two values would be equal if both were converted in the normal way associated with logical expressions. In C99, I think that (bool)a == (bool)b gives what I want. Is that correct? What is the normal way of writing this in traditional C?

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  • Looking for Reachability (2.0) Use Case Validation

    - by user350243
    There is so much info out there on using Apple's Reachability example, and so much is conflicting. I'm trying to find out of I'm using it (Reachability 2.0) correctly below. My App use case is this: If an internet connection is available through any means (wifi, LAN, Edge, 3G, etc.) a UIButton ("See More") is visible on various views. If no connection, the button is not visible. The "See More" part is NOT critical in any way to the app, it's just an add-on feature. "See More" could be visible or not anytime during the application lifecycle as connection is established or lost. Here's how I did it - Is this correct and/or is there a better way? Any help is Greatly Appreciated! lq // AppDelegate.h #import "RootViewController.h" @class Reachability; @interface AppDelegate : NSObject <UIApplicationDelegate> { UIWindow *window; UINavigationController *navigationController; RootViewController *rootViewController; Reachability* hostReach; // NOT USED: Reachability* internetReach; // NOT USED: Reachability* wifiReach; } @property (nonatomic, retain) IBOutlet UIWindow *window; @property (nonatomic, retain) IBOutlet UINavigationController *navigationController; @property (nonatomic, retain) IBOutlet RootViewController *rootViewController; @end // AppDelegate.m #import "AppDelegate.h" #import "Reachability.h" #define kHostName @"www.somewebsite.com" @implementation AppDelegate @synthesize window; @synthesize navigationController; @synthesize rootViewController; - (void) updateInterfaceWithReachability: (Reachability*) curReach { if(curReach == hostReach) { NetworkStatus netStatus = [curReach currentReachabilityStatus]; BOOL connectionRequired = [curReach connectionRequired]; // Set a Reachability BOOL value flag in rootViewController // to be referenced when opening various views if ((netStatus != ReachableViaWiFi) && (netStatus != ReachableViaWWAN)) { rootViewController.bConnection = (BOOL *)0; } else { rootViewController.bConnection = (BOOL *)1; } } } - (void) reachabilityChanged: (NSNotification* )note { Reachability* curReach = [note object]; NSParameterAssert([curReach isKindOfClass: [Reachability class]]); [self updateInterfaceWithReachability: curReach]; } - (void)applicationDidFinishLaunching:(UIApplication *)application { // NOTE: #DEFINE in Reachability.h: // #define kReachabilityChangedNotification @"kNetworkReachabilityChangedNotification" [[NSNotificationCenter defaultCenter] addObserver: self selector: @selector(reachabilityChanged:) name: kReachabilityChangedNotification object: nil]; hostReach = [[Reachability reachabilityWithHostName: kHostName] retain]; [hostReach startNotifer]; [self updateInterfaceWithReachability: hostReach]; [window addSubview:[navigationController view]]; [window makeKeyAndVisible]; } - (void)dealloc { [navigationController release]; [rootViewController release]; [window release]; [super dealloc]; } @end

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  • How to interpret Objective-C errors?

    - by Greg Maletic
    I'm getting the following error: 2010-05-11 17:46:28.475 MyApp[54112:5e1b] bool _WebTryThreadLock(bool), 0x140faa0: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now... Is there any way for me to figure out where [54112:5e1b] is in my code, so I can try to narrow down the error? Thanks.

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  • Using Func<...> and params?

    - by grady
    Hello, I wrote this code: public static bool MyMethod(int someid, params string[] types) {...} How could I write that using Func? public static Func < int, ?params?, bool > MyMethod = ??? Thanks :-)

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  • C++ Undeclared Identifier (but it is declared?)

    - by Joshua
    I'm pretty sure I've included the qanda class, but when I try to declare a vector that contains it or a class of that type I get an error saying that qanda is undefined. Any idea what the problem might be? bot_manager_item.h #pragma once #include "../bot_packet/bot_packet.h" #include <vector> class bot_manager_item; #include "qanda.h" #include "bot_manager.h" class bot_manager_item { public: bot_manager_item(bot_manager* mngr, const char* name, const char* work_dir); ~bot_manager_item(); bool startup(); void cleanup(); void on_push_event(bot_exchange_format f); bool disable; private: void apply_changes(); bot_manager *_mngr; std::string _name; std::string _work_dir; std::string _message; std::string _message_copy; std::vector<qanda> games; qanda test; char _config_full_path[2600]; }; qanda.h #ifndef Q_AND_A #define Q_AND_A #include "users.h" #include "..\bot_packet\bot_packet.h" #include "bot_manager.h" #include <string> #include <algorithm> #include <map> #include <vector> #include <fstream> class qanda { public: qanda(bot_manager * manager, std::string name, std::string directory); ~qanda(){}; void room_message(std::string username, std::string user_message); void timer_tick(); private: // data members std::string question; std::string answer; std::string directory; std::string command_prefix; std::string name; Users users; std::map <std::string, std::string> questions_and_answers; int time_per_question; // seconds int time_between_questions; // seconds int timer; // milliseconds bool is_delayed; bool is_playing; bot_manager * manager; // functions void new_question(); void send_message(std::string msg); void announce_question(); void load_questions(); }; #endif

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  • problem with fifos linux

    - by nunos
    I am having problem debugging why n_bytes in read_from_fifo function in client.c doesn't correspond to the value written to the fifo. It should only write 25 bytes but it tries to read a lot more (1836020505 bytes (!) to be exact). Any idea why this is happening? server.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> #include <sys/wait.h> #include <signal.h> #include <pthread.h> #include <sys/stat.h> typedef enum { false, true } bool; //first read the int with the number of bytes the data will have //then read that number of bytes bool read_from_fifo(int fd, char* var) { int n_bytes; if (read(fd, &n_bytes, sizeof(int))) { printf("going to read %d bytes\n", n_bytes); if (read(fd, var, n_bytes)) printf("read var\n"); else { printf("error in read var. errno: %d\n", errno); exit(-1); } } return true; } int main() { mkfifo("/tmp/foo", 0660); int fd = open("/tmp/foo", O_RDONLY); char var[100]; read_from_fifo(fd, var); printf("var: %s\n", var); return 0; } client.c: #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <fcntl.h> typedef enum { false, true } bool; //first write to fd a int with the number of bytes that will be written afterwards bool write_to_fifo(int fd, char* data) { int n_bytes = (strlen(data)) * sizeof(char); printf("going to write %d bytes\n", n_bytes); if (write(fd, &n_bytes, sizeof(int) != -1)) if (write(fd, data, n_bytes) != -1) return true; return false; } int main() { int fd = open("/tmp/foo", O_WRONLY); char data[] = "some random string abcdef"; write_to_fifo(fd, data); return 0; } Help is greatly appreciated. Thanks in advance.

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  • Problem with OOP Class Definitions

    - by oben
    Hi, this is Oben from Turkey. I work for my homework in C++ and i have some problems with multiply definitions. My graph class ; class Graph{ private: string name; //Graph name fstream* graphFile; //Graph's file protected: string opBuf; //Operations buffer int containsNode(string); //Query if a node is present Node* nodes; //Nodes in the graph int nofNodes; //Number of nodes in the graph public: static int nOfGraphs; //Number of graphs produced Graph(); //Constructors and destructor Graph(int); Graph(string); Graph(const Graph &); ~Graph(); string getGraphName(); //Get graph name bool addNode(string); //add a node to the graph bool deleteNode(string); //delete a node from the graph bool addEdge(string,string); //add an edge to the graph bool deleteEdge(string,string); //delete an edge from the graph void intersect(const Graph&); //intersect the graph with the <par> void unite(const Graph&); //intersect the graph with the <par> string toString(); //get string representation of the graph void acceptTraverse(BreadthFirst*); void acceptTraverse(DepthFirst *); }; and my traversal class; class Traversal { public: string *visitedNodes; virtual string traverse (const Graph & ); }; class BreadthFirst : public Traversal { public : BreadthFirst(); string traverse(); }; class DepthFirst : public Traversal { public : DepthFirst(); string traverse(); }; My problem is in traversal class , i need to declare Graph class at the same time , in graph class i need traversal class to declare. I have big problems with declerations :) Could you please help me ?

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  • help me understand the method Validator.TryValidateObject()

    - by Benny
    this is the method definition: public static bool TryValidateObject( Object instance, ValidationContext validationContext, ICollection<ValidationResult> validationResults, bool validateAllProperties ) what i am confused is the validateAllProperties parameter, I understand when it is true-validate all properties. What about when it is false, not validate all properties, but which property will be validated?

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