c# - MoreLinq Acquire. What does it do? -

i inspecting jon skeet's morelinq , became curious acquire extension source code

the implementation follows

        /// <summary>         /// ensures source sequence of <see cref="idisposable"/>          /// objects acquired successfully. if acquisition of          /// 1 <see cref="idisposable"/> fails          /// acquired till point disposed.         /// </summary>         /// <typeparam name="tsource">type of elements in <paramref name="source"/> sequence.</typeparam>         /// <param name="source">source sequence of <see cref="idisposable"/> objects.</param>         /// <returns>         /// returns array of acquired <see cref="idisposable"/>         /// object , in source order.         /// </returns>         /// <remarks>         /// operator executes immediately.         /// </remarks>          public static tsource[] acquire<tsource>(this ienumerable<tsource> source)             tsource : idisposable         {             if (source == null) throw new argumentnullexception("source");              var disposables = new list<tsource>();             try             {                 disposables.addrange(source);                 return disposables.toarray();             }             catch             {                 foreach (var disposable in disposables)                     disposable.dispose();                 throw;             }         } 

from understanding receives ienumerable<idisposable> , creates list<idisposable>.

i can't grasp whatever can go wrong here.

can explain me, , possibly provide example extension can useful?

the call addrange iterates on source. if reason encounters exception, had been acquired disposed. consider example:

var filenames = new[] { "file1.xml", "file2.xml", "doesnotexist.xml" }; var disposables = filenames.select(fn => file.openread(fn)); var filestreams = disposables.acquire(); 

no exception thrown when you're assigning disposables, because of lazy evaluation. however, when call addrange inside aquire reaches third element (where tries open "doesnotexist.xml"), filenotfoundexception thrown. when happens, acquire safely dispose previous streams. simple tolist / toarray leave first 2 file streams open.

in essence, acquire there ensure either all files in filenames safely opened, or none of them are.