Throwing exceptions in a constructor is perfectly fine in .Net. And in many circumstances, it is the Right Thing.
If a constructor cannot build a valid instance of a class, then it should throw an exception -- just like any other method. One key difference between virtual methods in .Net and in C++ is that, in .Net, the vtable for an object is fixed. As soon as the GC allocates space for the object, the CLR writes the vtable pointer (really, the type pointer) into the object header, and it NEVER changes after that point. You don't run into all of the ridiculous behaviors that you do in C++, with virtual function slots changing as you construct or destruct objects. By all means, if a constructor can't complete its work -- throw an exception! And, yes, the code that called "new foo()" will necessary not receive a reference to the object. That's by design. -- arlie -----Original Message----- From: Moderated discussion of advanced .NET topics. [mailto:[EMAIL PROTECTED] On Behalf Of Adam Straughan Sent: Thursday, April 01, 2004 2:50 AM To: [EMAIL PROTECTED] Subject: Re: [ADVANCED-DOTNET] Exceptions in Constructors Its still got bad idea stamped all over it. The object would not get constructed, this is almost certainly doc'd somewhere. The following code outputs the string "null" using System; public class MyClass { public static void Main() { A a = null; try { a = new A(); } catch(Exception){} if (a==null) Console.WriteLine("null"); else Console.WriteLine("not null"); } } class A { public A() { throw new Exception(""); } } > -----Original Message----- > From: Chris Snyder [mailto:[EMAIL PROTECTED] > Sent: 31 March 2004 15:30 > To: [EMAIL PROTECTED] > Subject: [ADVANCED-DOTNET] Exceptions in Constructors > > I have a (hopefully) simple question. > > In a nutshell, as a C++ developer, various people hammered into my > brain that throwing an exception in a constructor (whether > intentionally or by performing some action which would cause an > exception to be thrown) was extremely bad. However, my research seems > to indicate that .NET handles constructors differently, allowing > developers to perform actions in a constructor that may result in > exceptions being thrown, or to <gasp> even throw an exception > themselves. > > Thoughts? > > Thanks a lot, > Chris Snyder > > =================================== > This list is hosted by DevelopMentor(r) http://www.develop.com Some > .NET courses you may be interested in: > > NEW! Guerrilla ASP.NET, 17 May 2004, in Los Angeles > http://www.develop.com/courses/gaspdotnetls > > View archives and manage your subscription(s) at > http://discuss.develop.com > =================================== This list is hosted by DevelopMentorR http://www.develop.com Some .NET courses you may be interested in: NEW! Guerrilla ASP.NET, 17 May 2004, in Los Angeles http://www.develop.com/courses/gaspdotnetls View archives and manage your subscription(s) at http://discuss.develop.com =================================== This list is hosted by DevelopMentorŪ http://www.develop.com Some .NET courses you may be interested in: NEW! Guerrilla ASP.NET, 17 May 2004, in Los Angeles http://www.develop.com/courses/gaspdotnetls View archives and manage your subscription(s) at http://discuss.develop.com
