CODEWITHSUNDEEP
c#.netgenerics
Alec
Alec

Reputation: 1706

Does the generic list method Clear() use the method RemoveAt()?

I am writing a facade for IList<T> to implement change tracking. Does Clear use RemoveAt or Remove or something else entirely? I need to know if I need to set all the items tracking state inside of Clear or if changing the tracking state only in Remove, and RemoveAt will be enough.

Similarly, does Add use Insert? Does Remove or RemoveAt use each other?

Any other input into such an implementation is also welcome.

Edit: Do extension methods for List use pre-existing methods or is it new code? I don't know if I need to implement those as well.

Upvotes: 0

Views: 383

Answers (4)

jason
jason

Reputation: 241641

Does Clear use RemoveAt or Remove or something else entirely?

You can not rely on implementations of IList.Clear to use IList.RemoveAt or IList.Remove. It is up to the specific implementation to do whatever it wants.

Note that you can't even really rely on Clear actually removing all items from the instance. An interface does not enforce behavior, it is not actually a contract.

There's a huge misconception on what interfaces actually are. You'll hear people say that "interfaces are contracts". They are not. They merely specify that there will be some methods with certain signatures and return types that you will be able to invoke if you have an object that implements a given interface. That's it. There is no guarantee whatsoever on the implementation, or the behavior.

Additionally, relying on implementation details is a gigantic code smell. They could change on you at any moment without you knowing causing your code to fail and die miserably. Do not rely on implementation details.

Similarly, does Add use Insert?

Similarly, you can not rely on IList.Add using IList.Insert.

Does Remove or RemoveAt use each other?

You can not rely on it being true.

Upvotes: 6

Mike Mozhaev
Mike Mozhaev

Reputation: 2415

It doesn't matter if you write a facade since these methods are not virtual. Event if implementation of Clear called Remove (it doesn't) it wouldn't be your overriden Remove.

So that makes your life easier. You are free to implement this tracking fully in your wrapper.

Upvotes: 3

Bala R
Bala R

Reputation: 108957

From source, List<T> uses Array.Clear()

// Clears the contents of List.
public void Clear() { 
    if (_size > 0) 
    {
        Array.Clear(_items, 0, _size); // Don't need to doc this but we clear the elements so that the gc can reclaim the references. 
        _size = 0;
    }
    _version++;
}

Upvotes: 2

Matt Greer
Matt Greer

Reputation: 62027

IList is simply a contract. What a class implementing IList does behind the scenes is its own business and it doesn't have to make any promises. Some implementors might iterate through their items and call Remove against them, while others might just delete their backing store and create a new one, or many other possibilities.

It's probably not a good idea to assume someone implementing an interface implements it in a certain way. This is certain to break in unexpected ways at some point.

Upvotes: 2

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