c# - why object in collection of System.Linq.Enumerable.WhereSelectListIterator cannot be changed -

i use linq select data , returned type whereselectlistiterator. find object in whereselectlistiterator cannot modified, e.g., set null or update property of value. design? how make possible?

using system; using system.collections.generic; using system.linq;  namespace linqtest {     class program     {         static void main(string[] args)         {              var project = new project()             {                 sections = new list<section>()                 {                     new section()                     {                         outdated = new char[2]{'a','d'}                      },                     new section()                     {                         outdated = new char[2]{'a','d'}                      },                     new section()                     {                         outdated = new char[2]{'a','d'}                      }                 }             };               var dates = project.sections.select(t=>(new mystring(t.outdated)));             console.write(dates.elementat(0).description);             dates.elementat(0).description = "123";             console.write(dates.elementat(0).description);             console.read();          }     }       class mystring     {         public mystring(char[] abc)         {                 description = new string(abc).substring(1);         }         public string description { set; get; }     }     class project     {         public ienumerable<section> sections;     }     internal class section     {         public char[] outdated;      } } 

linq acts using yield operator on collection. if modify collection, invalidates iterator.

to workaround this, consider converting concrete class rather working ienumerable<t> calling toarray() or tolist() on ienumerable<t>.