Why Don't C# Arrays Explicitly Implement IList?

Understanding the Partial Implementation of IList in C# Arrays

While it's commonly assumed that C# arrays fully implement the IList interface, it's not the case. They only implement IList (the non-generic version). This apparent contradiction necessitates a deeper understanding.

Instead of explicitly implementing the generic IList interface, C# arrays benefit from a unique feature in the Common Language Runtime (CLR) known as "quacks-like-a-duck" typing. This means that the CLR treats arrays as if they implemented IList because they provide the necessary methods and properties.

However, this implementation is not entirely explicit. For instance, the Count property of IList is not directly exposed by arrays. Instead, the CLR provides an internal implementation that maps the Length property of arrays to the Count property.

This substitution allows arrays to seamlessly interact with code that expects an IList, even though they don't fully implement all of its methods. The CLR inserts the necessary conversion logic behind the scenes, making it appear as if arrays implement the interface.

This clever mechanism allows C# arrays to partially implement IList without explicitly declaring it, providing a convenient and efficient way to handle arrays in generic contexts. However, it's important to note that this implementation is dependent on the internal workings of the CLR and should not be relied upon in all scenarios.

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