为什么不IEnumerable <T> .Max约束T是IC可比的吗？

Question

If one calls the .Max() extension method on an IEnumerable<T> , and the objects within do not implement IComparable , one gets System.ArgumentException: At least one object must implement IComparable.

Why don't Max and similar methods constrain T to implement IComparable , so that this problem can be caught at compile time instead of at run time?

Answer 1

Comparisons are... fun. Firstly, you've got a choice of IComparable<T> or IComparable - which would you choose? Currently (via Comparer<T>.Default ) it supports both, but there is no "this or that" generic constraint.

Then you get the issue of Nullable<T> ; this has "lifted" comparisons, so whether it is comparable or not depends on the T ; but again, Comparer<T>.Default deals with this for us ( Nullable<T> implements neither IComparable nor IComparable<T> ).

Plus; it saves on generic constraint propagation; as soon as you have a constraint like this in library code, it quickly infects all the upstream calling code, making it a hard slog.

Answer 2

I guess because it's more flexible. For example, you may have an IEnumerable<object> which happens to contain strings, in which case Max() can be called quite safely on it, despite the fact that the type Object does not implement IComparable .