[Richard Suchenwirth] 2005-12-15 - A colleague wanted some sugar for [upvar] variables to [pass by reference], but as the use of ''xproc'' prevented the names of such procedures to end up in [tclIndex], we cooked up (it was lunch) this minimally invasive version: 
 proc use_refs {{char &}} {
    foreach v [uplevel 1 {info locals}] {
        if [string match $char* $v] {
            uplevel 1 "upvar 1 \${$v} [string range $v 1 end]"
        }
    }
 }
That's all. This command is preferrably called first inside a proc, and [upvar]s all arguments that begin with a specific character, the default being "&" - it runs code like
 upvar 1 ${&foo} foo
in the caller's scope. Testing:

 proc test_refs {a &b} {
    use_refs
    puts a=$a,b=$b
    set b new_value
 }
 % set bar 42
 42
 % test_refs foo bar
 a=foo,b=42
So the values of ''a'' and ''b'' are readable...
 % set bar
 new_value
...and the side effect of changing ''b'' in the caller did also happen.

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[Arts and crafts of Tcl-Tk programming]