CODEWITHSUNDEEP
c#.netinheritancelist
Joan Venge
Joan Venge

Reputation: 331260

Why can't I access the class internals of List<T> when I derive from it?

class NewList<T> : List<T>

Why can't I access it's internals like T[] _items, etc?

Why aren't they protected, but private?

Should I use composition for this?

Upvotes: 0

Views: 541

Answers (5)

JP Alioto
JP Alioto

Reputation: 45127

You don't need it. That is, what can you do with _items that you can't do with the Item : T property? They have given you a simple, functional abstraction to the underlying array with the indexer. It is very light weight -- all it does it check the bounds and increment the version of the list (on the setter) ...

var lst = new List<int>() { 1, 2, 3, 4, 5 };
lst[0].Dump(); // 1
lst.Dump(); // 1, 2, 3, 4, 5
lst[0] = 2;
lst.Dump(); // 2, 2, 3, 4, 5

Upvotes: 0

Henk Holterman
Henk Holterman

Reputation: 273494

It is by design, exposing members is only done when (absolutely) necessary, to let the object maintain a correct state at all times. And it is not a good idea to expose a field (_items) as protected, that would require a protected property. In this case, there already is a public property (this[])

Composition will give you even less access - no protected members either.

Upvotes: 1

Robert Harvey
Robert Harvey

Reputation: 180868

Why can't I access it's internals like T[] _items, etc?

Reflector says _items is private. The underscore suggests a private member

Why aren't they protected, but private?

In the case of _items, Microsoft provides the public ToArray method. It returns _items.

Upvotes: 1

Reed Copsey
Reed Copsey

Reputation: 564641

They're private because the author (Microsoft) did not intend for you to access them, probably for safety reasons.

You should use composition instead of inheritance. Make your class expose IList<T> instead of List<T> directly.

List<T> should never be directly exposed in a public API (this is actually specified in the design guidelines). It should be used as an internal implementation detail only.

Upvotes: 7

Andy
Andy

Reputation: 30418

List<T> isn't designed to be a base class. You should use one of the classes in System.Collections.ObjectModel instead.

Upvotes: 2

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