C# List<T> hides properties? [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

How does List<T> make IsReadOnly private when IsReadOnly is an interface member?

Okay, this is driving me nuts. List<T> implements IList<T>. However,

IList<int> list = new List<i开发者_如何学JAVAnt>();
bool b = list.IsReadOnly;
bool c = ((List<int>)list).IsReadOnly;    // Error

The error is:

'System.Collections.Generic.List' does not contain a definition for 'IsReadOnly' and no extension method 'IsReadOnly' accepting a first argument of type 'System.Collections.Generic.List' could be found (are you missing a using directive or an assembly reference?)

How can this be? Doesn't this violate the very rule that we tell everyone, about not hiding members? What is the implementation detail here?

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Because the implementation is via an explicit interface implementation.

Meaning that it's defined as

bool IList<T>.IsReadOnly { get; set; //etc }

http://msdn.microsoft.com/en-us/library/aa288461(VS.71).aspx

And that is why it's not off of List.

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List<T> implements IList<T> explicitly so you have to cast the object to the interface before being able to access IsReadOnly . From MSDN:

A class that implements an interface can explicitly implement a member of that interface. When a member is explicitly implemented, it cannot be accessed through a class instance, but only through an instance of the interface

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If you look at the List class, you'll see this:

 bool IList.IsReadOnly { [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]
        get; }

All that's really relevant is that IsReadOnly is declared using the explicit implementation which means that property can only be seen if the object is declared as that of IList.

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Explicit interface implementation, something like:

bool IList<T>.IsReadOnly { get; }