Why Does the .NET Array Class Implement the IList Interface?

Why the Array Class Implements the IList Interface

The .NET Framework definition of the System.Array class indicates that it inherits from, among other interfaces, the IList interface. This raises the question: why would an array implement an interface designed for lists?

The answer lies in the nature of arrays. Arrays provide fast indexed access to their elements, a feature supported by both the IList and IList interfaces. This makes it possible to cast an array to an IList object, as in the example provided in the original question.

However, while an array implements the IList interface, it does not fully conform to its specifications. Attempting to modify the array through the IList object results in an exception. This is because arrays are designed to be fixed-size collections, whereas lists can be resized dynamically.

The reason for this discrepancy is that there is no dedicated interface for constant-sized collections with indexers. While the IList interface provides a common interface for lists, it does not distinguish between resizable and constant-sized collections.

As such, the use of the IList interface for arrays is a compromise that allows for indexed access to array elements while maintaining the underlying fixed-size nature of arrays. It is important to note, however, that this compromise does not allow for full compatibility with all methods of the IList interface.

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