Question

Does the Any method in LINQ iterated over the entire collection or return true when the first successful iteration occurs?

Answer 1

The Any method will only iterate over the minimum number of elements necessary. As soon as it finds a matching element it will return immediately

It’s roughly implemented as follows

public static bool Any<T>(this IEnumerable<T> enumerable, Func<T, bool> predicate) {
  foreach (var cur in enumerable) {
    if (predicate(cur)) { 
      return true;
    }
  }
  return false;
}

In the worst case (none or last matching) it will visit all elements. In the best case (first matching) it will only visit 1