'''`[namespace] upvar`''' makes a variable a link to the specified [namespace] [variable]. 



** Synopsis **

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



** Description **

Links a namespace variable named ''otherVar'', which may contain
[namespace%|%namespace qualifiers] and is resolved relative to ''namespace'',
into the the current [level] as ''myVar'', which also may contain [namespace
qualifiers.

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].



** [RFE]: One and Two-argument Case **

'''[PYK] 2018-05-14:'''

`namespace upvar` could support a two-argument case where the current namespace
is implied.  It could also support a one-argument case where the one argument
is a list of alternating namespace and local names.


<<categories>> command | namespace | Tcl syntax help