c# - Does calling Count on IEnumerable iterate the whole collection? -

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• difference between ienumerable count() , length 3 answers

consider following code:

static ienumerable<int> getitems() {     return enumerable.range(1, 10000000).toarray();  // or: .tolist(); }  static void main() {     int count = getitems().count(); } 

will iterate on 10 billion integers , count them one-by-one, or use array's length / list's count properties?

if ienumerable icollection, return count property.

here's source code:

public static int count<tsource>(this ienumerable<tsource> source) {     if (source == null) throw error.argumentnull("source");     icollection<tsource> collectionoft = source icollection<tsource>;     if (collectionoft != null) return collectionoft.count;     icollection collection = source icollection;     if (collection != null) return collection.count;     int count = 0;     using (ienumerator<tsource> e = source.getenumerator())     {         checked         {             while (e.movenext()) count++;         }     }     return count; } 

an array implements icollection<t>, doesn't need enumerated.