As from 8.5, [lassign] is in the Tcl core - see [Changes in Tcl/Tk 8.5].

[TclX] has supplied lassign since the early [[or mid-?]] '90s.
   [http://www.tcl.tk/man/tcl/TclCmd/lassign.htm%|%official reference]:   
Example usage:
    lassign {value1 value2} variable1 variable2
in place of
    set variable1 value1
    set variable2 value2
   [TIP] [http://purl.org/tcl/tip/57.html%|%57]:   proposed making the [TclX] `lassign` command a built-in Tcl command 
** Description **
----

Actually, note that lassign takes a list and assigns each
element to a variable.  Thus, while the above is true,
the list of values can have dozens of elements.























----
[DKF] cleverly points out that lassign makes a Perlish [[shift]] this easy:
      proc shift {} {
          global argv
          set argv [lassign $argv v]
          return $v
      }
On the other hand, [Hemang Lavana] observes that TclXers already
have "[lvarpop] ::argv", an exact synonym for "shift".