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.NET Forum / Languages / C# / February 2008Replacement for CTypedPtrList
I am converting a C++ project management program I wrote to C#. Each Protask obect represent a task and includes two CTypedPtrList objects: the lists of pointers to the prerequisite tasks and dependent tasks. There doesn't seem to be an equivalent to the CTypedPtrList in C#. I'm not sure if ArrayList or a List(T) generic would best fill the requirement. I am guessing that regardless of which I use, I will need to use the unsafe keyword to use pointers. Would a List(T) generic list be safer than an ArrayList? Any thoughts would be most appreciated. Bob I'm not familiar with CTypedPtrList, but from your description it sounds like List<T>, where T is a class (not a struct): * each item is a reference * each item is strongly typed i.e. public sealed class Protask { private readonly List<Protask> preRequisites = new List<Protask>(), dependents = new List<Protask>(); public List<Protask> PreRequisites { get { return preRequisites; } } public List<Protask> Dependents { get { return dependents; } } } Of course, you might want to encapsulate the lists a bit more if you want editing one to automatically update the other end (if you see what I mean). Marc Hello Marc, Thank you for your reply. Can T be a pointer to a class? > I'm not familiar with CTypedPtrList, but from your description it > sounds like List<T>, where T is a class (not a struct): [quoted text clipped - 20 lines] > > Marc Robert, You don't have pointers to classes in .NET, you have references (there is a difference). But yes, T can be a reference type, where the List<T> is the list of reference types. This means that when you access an item from the List<T>, you will get a reference that points to the same item that the reference in List<T> points to (whereas if T was a struct, you would get a copy on return because of the copy semantics of structures on assignment).  Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com > Hello Marc, > [quoted text clipped - 24 lines] >> >> Marc Hello Nicholas, I'm still not sure if I understand this correctly. Does a List<T> object holds a bunch of objects of type T or Does it only hold the references (addresses?) of those objects? I certainly don't want each task to hold copies of all its prerequisites and dependent tasks. Thanks, Bob > Robert, > [quoted text clipped - 34 lines] >>> >>> Marc > I'm still not sure if I understand this correctly. > Does a List<T> object holds a bunch of objects of type T or > Does it only hold the references (addresses?) of those objects? > > I certainly don't want each task to hold copies of all its prerequisites and > dependent tasks. Assuming T is a reference type (e.g. a class) then it only holds references. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Thank You! >> I'm still not sure if I understand this correctly. >> Does a List<T> object holds a bunch of objects of type T or [quoted text clipped - 6 lines] > Assuming T is a reference type (e.g. a class) then it only holds > references. As Jon has stated - references; that is why I added my "where T is a class (not a struct)" caveat to my original reply. In .NET, and very unlike C++, there is a large and fundamental difference between "struct" and "class". A struct (examples: int, float, DateTime, etc) follows value-type semantics, and will copy itself (memcopy) sooner than you can glance at it - i.e. int x = 5; int y = x; // [memcopy of the struct] Because of this, structs are almots always immutable (non-editable once created), because it just gets too confusing to think about them otherwise. In contrast, classes have reference-type semantics. "new" creates a new object on the managed heap, and the field/variable just holds the referenece (think: pointer). Most .NET types are classes. Assignment of variables copies *the reference*, not the object: Foo x = new Foo(); Foo y = x; // reference value is copied, both x & y point to same Foo Marc Thank you! > As Jon has stated - references; that is why I added my "where T is a > class (not a struct)" caveat to my original reply. [quoted text clipped - 20 lines] > > Marc Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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