Question

Let us assume the code I use to iterate through a node list

foreach(XmlNode nodeP in node.SelectNodes('Property')) {   propsList.Add(nodeP.Attributes['name'].Value, true); } 

in this case does the expression node.SelectNodes(‘Property’) , get evaluated during each iteration of for each or once?

Answer 1

Only once. The foreach statement is syntactic sugar for (in your case)…

{     IEnumerator<XmlNode> enumerator = node.SelectNodes('Property').GetEnumerator();      XmlNode nodeP;      while(enumerator.MoveNext())     {         nodeP = enumerator.Current;          propsList.Add(nodeP.Attributes['name'].Value, true);     }      IDisposable disposable = enumerator as IDisposable;      if(disposable != null) disposable.Dispose(); } 

So the actual call to SelectNodes() only happens one time.