Is this C# 'closure' still valid across a parameter reference? -

let's take simple case .net smtpclient, can following (ignoring credentials, ssl , exception handling):

async task sendmail() {     var m = new mailmessage(...);     var s = new smtpclient(host, port);      s.sendcompleted += (s, e) => { m.dispose(); s.dispose(); };       await s.sendmailasync(m); } 

all fine; func dispose()ing called whenever async sending finishes. m , s within containing scope declared, no problem there.

but had following:

smtpclient setupmailclient(mailmessage mail) {     var smtpclient = new smtpclient(host, port);      smtpclient.sendcompleted += (s, e) => { mail.dispose(); smtpclient.dispose(); };      return smtpclient; }  async task sendmail() {     var m = new mailmessage(...);     var s = setupmailclient(m);      await s.sendmailasync(m); } 

now, calling await sendmail() still safe? closure still valid? pass in reference mailmessage 'mail' - copy of reference, valid in context of setupmailclient(). overthinking it, or still safe usage?

both programs behave identically. second program more confusing follow, in sendmail method creating mailmessage, 1 responsible disposing of (by convention). doesn't dispose of object , method calls confuse others reading code. should have sendmail dispose of mailmessage in case (which can trivially done wrapping in using.

we pass in reference mailmessage 'mail' - copy of reference, valid in context of setupmailclient().

it's not valid in context of setupmailclient. it's valid reference entire lifetime of object. it's in scope in context of setupmailclient, meaning code within method allowed refer parameter name. scope , lifetime different concepts. scope of mail method, lifetime of variable can (and in case is) longer until method returns (due closure).