Custom Collection and Inherited Class Types

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I'm having difficulty, probably missing something simple, with queuing and unqueuing items in a collection.

I have classes with various levels of inheritance:

public abstract class Item
{  //stuff }

public class DetailItem : Item
{  //stuff }

public class SuperDetailItem : DetailItem
{  //stuff }

public class OddItem : Item
{  //stuff }

I then have a ConcurrentQueue<T> like so:

public class CQItems<Item> : ConcurrentQueue<Item>
{  //some methods }

One of the methods adds items when called, so I do something like:

CQItems<Item> items = new CQItems<Item>();

It'll create i items in the queue. This works, though currently in the method I am specifying creating DetailItem items - I'd like to have that be dynamic if possible as well, but that'll be a different question. So later, I call to get a DetailItem out like so:

 DetailItem item;

 items.TryDequeue(out item);

and get the message "Cannot convert from DetailItem to Item".

I don't want to make a specific collection for each inherited type. What piece am I missing? Thanks!

answered question

1 Answer


Firstly you create a queue which is supposed to store Item elements.

CQItems<Item> items = new CQItems<Item>();

Then you say: take whatever concrete type deriving from Item you have and assign it to DetailItem variable:

DetailItem item;
items.TryDequeue(out item);

TryDequeue "returns" an Item via out modifier. This is basically the same thing as if you tried to assign an Item to a DetailedItem like so:

Item item = GetItem();
DetailedItem detailedItem = item; // compilation error

Which obviously makes no sense.

The "Try" part in TryDequeue corresponds to the empty queue, not to the casting.

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