Why does List<T> implement IReadOnlyList<T> in .NET 4.5?
List<T> isn't read only...
Because List<T> implements all of the necessary methods/properties/etc. (and then some) of IReadOnlyList<T>. An interface is a contract that says "I can do at least these things."
The documentation for
IReadOnlyList<T>says it represents a read-only collection of elements.
That's right. There are no mutator methods in that interface. That's what read-only means, right? IReadOnlyList<T> is used in the "typical" (contract) way, not as a marker.