[NEM] ''26 Aug 2006'': [C#] has a nice little construct for automatically
closing a resource once you are finished with it. Here's a Tcl version
of this ''using'' command:

 proc using {varName chan script} {
     upvar 1 $varName var
     set var $chan
     set rc [catch { uplevel 1 $script } result]
     catch { close $chan }
     return -code $rc $result
 }

Which you can then use like:
 using fd [open somefile.txt] { puts [read $fd] }
or
 foreach host $hosts {
     using sock [socket $host $port] { ... do stuff on $host ... }
 }

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