c# - Parallel.ForEach over AuthorizationRuleCollection -

hopefully point out doing wrong here. have process reads in file access rules , trying run in parallel.

here code have far:

public list<folderaccessrule> getsecuritygroupsforfolder(long importid, string subdirectory, bool includeinherited)     {         concurrentqueue<folderaccessrule> groups = new concurrentqueue<folderaccessrule>();         concurrentqueue<exception> exceptions = new concurrentqueue<exception>();          directoryinfo dinfo = new directoryinfo(subdirectory);         directorysecurity dsecurity = dinfo.getaccesscontrol();          authorizationrulecollection authorizationrulecollection = dsecurity.getaccessrules(true, includeinherited, typeof(ntaccount));         parallel.foreach( authorizationrulecollection,             fsar =>             {                 try                 {                     folderaccessrule group = this.getgroup(fsar);                     if (group != null)                     {                         groups.enqueue(group);                     }                 }                 catch (exception e)                 {                     exceptions.enqueue(e);                 }             });          foreach (exception e in exceptions)         {             string message = string.concat(e.gettype(), "exception getting directory info  ", subdirectory);             this.recordexception(message, subdirectory, e);         }          return groups.tolist();     } 

which (to untrained eye), looks should work. parallel.foreach not compile gives error:

the type arguments method 'system.threading.tasks.parallel.foreach<tsource> (system.collections.generic.ienumerable<tsource>, system.action<tsource>)' cannot inferred usage. try specifying type arguments explicitly. 

i have tried changing offending line to:

parallel.foreach<filesystemaccessrule>( authorizationrulecollection, fsar => 

but still no joy.

so, doing wrong? in advance.

pass authorizationrulecollection.oftype<authorizationrule>() parallel.foreach, eg:

var typedcolletion=authorizationrulecollection.oftype<authorizationrule>(); parallel.foreach(typedcolletion); 

the error caused because authorizationrulecollection doesn't implement ienumerable<t> ienumerable, elements object. common pattern older (pre - .net 2.0) collections, when generics weren't available.

newer .net classes return/expect generic collections. calling oftype<t>() or cast<t>() cast source ienumerable ienumerable<t>.

the difference oftype<t>() filter out incompatible elements, while cast<t>() throw if incompatible elements found.

the code behind both methods isn't magic, in reference source it's iterator on source ienumerable:

    public static ienumerable<tresult> oftype<tresult>(this ienumerable source) {         if (source == null) throw error.argumentnull("source");         return oftypeiterator<tresult>(source);     }      static ienumerable<tresult> oftypeiterator<tresult>(ienumerable source) {         foreach (object obj in source) {             if (obj tresult) yield return (tresult)obj;         }     }