c# - performance of linq extension method ElementAt -

the msdn library entry enumerable.elementat(tsource) method says

"if type of source implements ilist, implementation used obtain element @ specified index. otherwise, method obtains specified element."

let's have following example:

        icollection<int> col = new list<int>() { /* fill items */ };         ilist<int> list = new list<int>() { /* fill items */ };          col.elementat(10000000);         list.elementat(10000000); 

is there difference in execution? or elementat recognize col implements ilist<> although it's declared icollection<>?

thanks

the type of variable irrelevant elementat method - far it's concerned, it's declared ienumerable<t>, because that's parameter type is. (both calls bound same extension method.)

it's execution-time type of object tested in elementat.