C# 4.0 Unleashed

Interface-Based Constraints

An example is in order. Suppose we want to create a collection that can keep elements sorted. To make the collection maximally applicable, we want to declare it as a generic type. However, just creating an OrderedList<T> is too permissive because not every type is suitable for sorting purposes. So we want to constrain the flexibility on the type parameter T by saying we only allow “types T that are orderable.” What makes a type orderable? That starts to smell like a contract, something that can be enforced by the implementation of a certain interface. IComparable<T> comes to mind:

If we can compare any two objects of ...