'''`[namespace] upvar`''' creates an alias to a namespace variable.



** Synopsis **

    :   '''namespace upvar''' ''namespace otherVar myVar'' ?''otherVar myVar ...''?



** Description **

Resolves a variable named ''otherVar'', which may contain [namespace%|%namespace
qualifiers], relative to ''namespace'' and makes ''myVar'', which also may
contain [namespace qualifiers], an alias in the current [level] for
that variable.

It is an error for ''otherVar'' and ''myVar'' to resolve to the same variable
unless that variable is already a name for some other variable.  This makes it
possible to determine whether a variable is an alias.

`namespace upvar` is a convenience command that doesn't add any functionality
not previously available with `[upvar]`.  The following are equivalent:

======
set ns ::foo
upvar #0 ${ns}::bar boo
======

and

======
set ns ::foo
namespace upvar $ns bar boo
======

However, the second form is more efficient as it requires less string manipulation and parsing.


In contrast to `[variable]` `namespace upvar` provides the ability to give the
variable an arbitrary name :

======
proc myproc {} {
    variable var1
    namespace upvar [namespace current] var1 myvar1
}
======





[DKF]: `namespace upvar` was created to help accelerate [Snit].



** See Also **

   [namespace]:   the primary command for working with namespaces

<<categories>> Command | Tcl syntax help